AMOS-ICSHMO 2018

ABSTRACT BOOK

PART 1

ORAL PRESENTATIONS

5-9 February 2017 UNSW, Sydney, Australia The ARC Centre of Excellence for Extremes (CLEX) is the world’s first fully integrated research centre focused on understanding and predicting climate extremes.

Research programs

Heatwaves Climate Extreme and cold air Drought variability and rainfall outbreaks teleconnections

5106-clex-press-ad-1-v2.indd 1 16/1/18 6:06 pm Table of Contents

Plenary Sessions ...... 1 Climate change science and solutions for Australia and our region ...... 1 Drivers of recent oceanic trends around from the surface to the abyss ...... 2 Natural drivers of interannual to decadal variations in surface climate ...... 4 Global warming and coral reefs ...... 5 Tropical cyclones and the global energy budget: their role and implications ...... 6 Characterizing benefits of mitigation and avoided impacts, especially in the context of the Paris warming targets ...... 7 Communicating science ...... 8 Theme 1: Oceanographic Processes and Observations ...... 9 1.1 Variability and change in the Indo-Pacific and Australian regional seas – A session in honour of Gary Meyers ...... 9 Gary Meyers – A scientific life well lived ...... 9 Progress in understanding and predicting the IOD and its impacts ...... 10 Mean subsurface upwelling induced by intraseasonal variability in the equatorial Indian Ocean ...... 11 Interannual variability of the Indonesian Throughflow transport: a revisit based on 30-year expendable bathythermograph data ...... 12 Potential Origins of Pacific Decadal Variability ...... 13 Evidence of a super-convergence zone in the subtropical Indo-Pacific Ocean ...... 14 Northern boundary circulation properties of the South Australian Current System based on a gridded hydrography ...... 15 Building on the legacy of Gary Meyers, inaugural director of Australia’s Integrated Marine Observing System (IMOS) ...... 16 A decade of Integrated Marine Observing (imos) in Western Australia: Legacy and vision of Gary Meyers ...... 17 Extreme marine warming across tropical Australia during austral summer 2015-2016 ...... 18 1.2 Physical oceanography in the Southern Ocean and at the Antarctic margins...... 19 Convection in the Southern Ocean – What controls it? ...... 19 Impacts of broad-scale surface freshening of the Southern Ocean in a coupled climate model . 20 Antarctic sea-ice trends sustained by vertical ocean heat redistribution ...... 21 22-year surface changes in the seasonal ice zone near 140°e off Antarctica ...... 22 The role of convection in driving mixing in the Southern Ocean ...... 23 An Indian Deep Water pathway along the south coast of Australia ...... 24 The impact of localised dense water overflows on ocean heat transport towards Antarctica .... 25 Geothermal heating enhancing upwelling in the Antarctic Circumpolar Current ...... 26

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Deep bottom mixed layer instability drives intrinsic variability of the Antarctic Slope Front ...... 27 Intercomparison of Antarctic ocean/sea-ice/ice-shelf interactions simulated by two models ... 28 Anatomy of a glacial meltwater discharge event in an Antarctic cove ...... 29 On the importance of the circulation induced by ice-shelf melt for heat exchanges across the Antarctic continental shelf ...... 30 Increased basal melting of the Mertz Glacier Tongue after calving ...... 31 Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water ...... 32 Hotspot of carbon fluxes along the Polar Front ...... 33 Eddies lengthen streamlines at standing meanders as observed by Argo floats ...... 34 New perspectives on Southern Ocean jets, fronts and their variability ...... 35 Fingerprints of eddy stirring suppression in Antarctic Circumpolar Current jets ...... 36 1.3 Ocean extreme events and their impacts ...... 37 Prediction of extreme ocean conditions in Australia ...... 37 Multi-year persistence of the 2014/15 North Pacific marine heatwave ...... 38 Coral bleaching pathways under the control of regional temperature variability ...... 39 Australian Wave Setup Hindcast ...... 40 Marine heatwaves in the South Atlantic ...... 41 1.4 Collaborative Research under the Centre for Southern Hemisphere Ocean Research (CSHOR) 42 Centre for Southern Hemisphere Oceans Research (CSHOR) ...... 42 Unusually warm Indian Ocean sea surface temperatures arrest development of El Niño in 2014 ...... 43 The acceleration and 60 year oscillation in global sea levels ...... 44 The CSHOR Southern Ocean Dynamics Project ...... 45 Response of tropical Pacific climate variability to multi-decadal high latitude forcing ...... 46 Using past changes to improve models of the Antarctic Ice Sheet ...... 47 The increasing rate of global mean sea-level rise during 1993-2014 ...... 48 Coupled atmosphere-ocean dynamics in the eastern Indian Ocean warm pool ...... 49 An episodic change in the SST- relationship during boreal spring in the western tropical Pacific and its associated atmospheric teleconnections ...... 50 1.5 South Atlantic Ocean: circulation, processes, observations and modelling ...... 51 Climate drivers of the South Atlantic Subtropical Mode Water ...... 51 A budget analysis of the SAMOC at 22°S and 34.5°S using observational based reconstruction 52 Impact of mesoscale dynamics in the South Atlantic and the Agulhas region on the South Atlantic Meridional Overturning Circulation ...... 53 1.6 Oceanic pathways from the Subtropical Southwest Pacific ...... 54 Trends and Variability in the Southwest Pacific ...... 54

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Projected changes in southwest Pacific Ocean circulation and temperature extremes in a future climate...... 55 Variability of the subtropical mode water in the Southwest Pacific ...... 56 Direct observations of western boundary currents off northeastern Australia: seasonality and vertical structure ...... 57 1.7 Sea-level science: from surface waves to global change ...... 58 Predicting extreme water levels around Australia ...... 58 Seasonal Sea-Level Patterns and Predictions around Australia ...... 59 Coupled wave climate and sea-level change during past analogues of tropical expansion ...... 60 High-resolution sea level projections for the Australian region in the 21st century ...... 61 1.8 Ocean variability on timescales from days to decades ...... 62 Spectral descriptions of coastal submesoscale surface currents and passive tracers in an observational view ...... 62 Intercomparison of Two Analogous Western Boundary Currents...... 63 Characterisation and retention by East Australian Current meso-scale eddies: a Lagrangian approach ...... 64 Global Estimates of Mesoscale Mixing from High Resolution Sea Surface Temperature Satellite Data ...... 65 Buoyancy driven ocean gyres ...... 66 Temperature variability inshore of the Agulhas Current, from submesoscale to multidecadal .. 67 Fine-scale satellite altimeter observations in the Southern Hemisphere: opportunities and challenges ...... 68 Indian Ocean Dominance in Upper Ocean Heat Uptake since 2005: A global Perspective ...... 69 Transport and energy conversion pathways along southeastern Australia (31.5-34.5oS) ...... 70 Frontal Eddies in the East Australian Current System ...... 71 Characterising the cross-shore variability of internal tides at 27.5°s off east Australia ...... 72 Spatio-temporal Variations of Mesoscale Eddies in the Sulu Sea ...... 73 1.9 Advances in ocean modelling and prediction ...... 74 Surface drift and the search for MH370 ...... 74 Nested high-resolution atmosphere and ocean-4DVar assimilative system for the west coast of Australia ...... 75 Assimilation of Northwestern Tropical Pacific moored velocity data in a regional ocean modeling: Low frequency capabilities ...... 76 Observation impact from a regional reanalysis of the East Australian Current ...... 77 Towards biogeochemical modelling of the East Australian Current system ...... 78 Numerical Experiments on Determining the Impacts of Channel Bends and Channel Bathymetry in Sydney Estuary Circulations, NSW ...... 79 The Horizontal Residual Mean: addressing the limited spatial resolution of models ...... 80

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Sensitivity of numerical ocean models to the choice of isopycnal mixing directions in rotated diffusion tensors ...... 81 ACCESS-OM2 Ocean-Ice Model: progress and plans ...... 82 Attributing contributions to spurious mixing in an Arbitrary Lagrangian-Eulerian ocean model 83 The role of convection in driving geostrophic gyres and overturning circulation ...... 84 Modelling Spectral Dissipation due to Wave Breaking for Ocean Wind Waves Model Performance for Light to Hurricane Wind Speeds ...... 85 1.10 Oceans – general ...... 86 Fluorescence impact on Raman remote sensing of water temperature ...... 86 The role of bottom-intensified mixing in an overturning circulation maintained by surface buoyancy forcing ...... 87 The influence of air-sea flux products, albedo and the depth penetrative effect of short wave radiation on upper ocean overturning circulation...... 88 Exploring the ocean response to anthropogenic aerosol forcing ...... 89 Theme 2: Atmospheric Processes ...... 90 2.1 Observations – Atmospheric, marine and remote ...... 90 The SWIO-TC Experiment: A field campaign to improve understanding and prediction of tropical cyclones and their impacts in the SW Indian Ocean ...... 90 Polarsonde observations of clouds and aerosols in a Southern Ocean frontal passage ...... 91 Comparison between Dobson and zenith-DOAS measurements of total ozone columns over Melbourne and an investigation of derivation algorithms ...... 92 Forecast sensitivity to observations in ACCESS numerical weather prediction ...... 93 Three dimensional tomographic reconstruction of rainfall using satellite signals ...... 94 The Australian Wind Profiler Network for Operations and Research ...... 95 2.2 Atmospheric and oceanic chemistry in the earth system: insights from the Southern Hemisphere ...... 96 Biomass Burning Emissions in the Southern Hemisphere ...... 96 Characterising terrestrial influence in the remote Southern Ocean ...... 97 Comparison of mid-latutude springtime ozone in northern and southern hemispheres ...... 98 A new scheme for dry deposition of ozone to the ocean and its impact on global deposition budget ...... 99 Aerosol and cloud profiling with surface-based lidars...... 100 Radiation, cloud and precipitation response to global perturbations of dimethyl sulfide ...... 101 Improved understanding of biogenic emissions, chemistry and impacts in Southeast Australia ...... 102 Aliphatic Aldehydes as Photolytic Sources of H2 in the atmosphere ...... 103 Statistical modelling of airborne grass pollen ...... 104 The importance of the ground state in the atmospheric photochemistry of carbonyls ...... 105

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Grass pollen dispersion modelling in SE Australia with the CSIRO-CTM: Preliminary results .... 106 Ocean – Atmospheric interaction studies using 11 year CALIPSO Lidar measurements ...... 107 2.3 Clouds and convective processes...... 108 How organised is extreme rainfall in Australia, as seen from satellite observations? ...... 108 The universal scaling characteristics of tropical oceanic rain clusters ...... 109 Convective-environment interaction explored by linear response matrix ...... 110 Implementing the stochastic multi cloud model (SMCM) into the ICON global climate model 111 Radiative-Convective Equilibrium and organized convection – An observational perspective . 112 The impacts of lower stratospheric stability changes on deep convective transport ...... 113 A thermodynamic constraint on the depth of the global tropospheric circulation ...... 114 2.4 Australia-Asian monsoon and their interactions in current and future climate ...... 115 A comparison of onset definitions for the North Australian Monsoon ...... 115 Trends, variability and extremes of maritime continent rainfall: a weather regimes perspective ...... 116 The dynamics of Australian monsoon bursts in coupled climate models ...... 117 GCM precipitation biases in Australian monsoon and maritime continent linked to temporal and spatial intermittency of sub-daily precipitation ...... 118 Monsoons and tropical rainfall in models and observations ...... 119 East Asian monsoon forecast skill in ACCESS-S1 and sensitivity to land-surface initial conditions ...... 120 Rossby wave theory in a horizontally nonuniform basic flowand Asian-Australian monsoon interaction ...... 121 Diagnosing remote and locally forced systematic errors in monsoon simulations ...... 122 Inter‑decadal changes in the East Asian summer monsoon and associations with sea surface temperature anomaly in the South Indian Ocean ...... 123 Impacts of the Indian Ocean Dipole on the summer water vapour transport into the South China Sea region ...... 124 Australian-Asian monsoon under BoM-CMA collaborative research: progress and prospects . 125 Characteristics of water vapour transport and atmospheric river analysis in Asian-Australian Region: A CMA-BoM bilateral project ...... 126 Continental atmospheric rivers over China and Australia: two case studies ...... 127 An analysis of atmospheric rivers embedded in the monsoonal flows and associated heavy rainfall events over China and Australia ...... 128 Tempo-spatial distributions and variations of atmospheric rivers affecting Australia and East Asia ...... 129 Atmospheric river analysis: diagnosing heavy precipitation based on the convergence of integrated water vapour flux and a column saturation index ...... 130 Sensitivity of future Australian summer monsoon rainfall to emission scenario ...... 131

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Impact of recent deforestation on the climate of South-East Asia ...... 132 The anthropogenic contribution to Asia–Australia monsoon system changes ...... 133 2.5 Large-scale atmospheric and climate dynamics of the Southern Hemisphere ...... 134 Exploring the tropical drivers of the Antarctic atmosphere ...... 134 Split Jet variability in the South Pacific Winter ...... 135 Understanding the seasonal cycle of tropical precipitation: a convective quasi-equilibrium model ...... 136 Changes in southern hemisphere explosive storms in a warming climate ...... 137 Monsoon depressions in southern Africa: The Angola Low ...... 138 Intraseasonal periodicity in the southern hemisphere circulation on synoptic spatial scales ... 139 2.6 Atmospheric – general ...... 140 Meteorological controls on atmospheric particulate pollution during hazard reduction burns 140 Regime based evaluation of present day GCM cloud simulations using self organizing maps .. 141 Testing a new hypothesis that increasing use of irrigation water is causing global warming .... 142 Theme 3: Climate ...... 143 3.1 Changes in atmospheric circulation and Southern Hemisphere regional climate ...... 143 A novel investigation of the impact of anthropogenic forcing on the high-latitude southern hemisphere circulation ...... 143 Activity of the Southern Annular Mode during 2015-2016 El Niño event and its impact on Southern Hemisphere climate anomalies ...... 144 Changes in the mean meridional circulation and its impact on the climate of Victoria ...... 145 Detecting surface climate changes due to ozone change using ‘weather@home’ ...... 146 An energetic perspective into the variability of atmospheric circulations ...... 147 3.2 Tropical Indo-Pacific variability: dynamics, teleconnections and impacts ...... 148 Pacific meridional modes and tropical decadal variability: past and future ...... 148 Understanding ENSO event precursors ...... 149 Global warm-to-cold ocean heat transport controlled by the Eastern Pacific Cold Tongue ...... 150 Inability of CMIP5 climate models to simulate recent multi-decadal temperature change in the pacific ...... 151 “Statistical Challenges in Climatology”: Outcomes from a joint Bureau of Meteorology/ACEMS workshop ...... 152 Multi-year ENSO prediction ...... 153 Future changes in Extreme El Nino events modulated by North Tropical Atlantic variability ... 154 Causes and predictability of the negative Indian Ocean Dipole and its impact on La Niña during 2016 ...... 155 Regional changes to the remote impacts of the El Niño-Southern Oscillation ...... 156 ENSO diversity in CMIP5 models and its relation to co-varying dynamics ...... 157

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Has El Niño changed its flavour? Recent changes in a multi-century context ...... 158 The impact of strong El Niño events on east Australian spring rainfall ...... 159 A potential for La Nina-like climate change in the ENSO Recharge-Oscillator framework ...... 160 3.3 Maritime Continent earth system science for improved understanding and prediction of its local variability and global impact ...... 161 Intraseasonal variation in convective and stratiform rain in the Maritime Continent ...... 161 Sea surface salinity variations in the Maritime Continent region and the relationships with monsoon, El Nino, and ocean currents ...... 162 Diurnal cycle of convection and circulation: weather-climate processes over the Maritime Continent ...... 163 Assessing the impacts of coupling frequency on rainfall over the western Maritime Continent ...... 164 Maritime Continent land-sea breeze structure revealed by scatterometer data ...... 165 Intraseasonal oscillations and embedding convection-coupled disturbances in South China Sea and surrounding areas ...... 166 Predictable patterns of rainfall and atmospheric circulation over the Maritime Continent and adjacent regions: role of air-sea interaction and seasonal dependence ...... 167 3.4 South American climate variability, change and predictability ...... 168 Testing for collective significance of temperature trends ...... 168 Rainfall variability over South America associated with SST anomalies in South Pacific and South Atlantic oceans ...... 169 Air-sea interactions in the Western South Atlantic and regional climate impacts ...... 170 Impact of atmospheric blocking on South America in austral summer ...... 171 3.5 Climate of the tropical Pacific Islands ...... 172 Diurnal variations of rainfall in surface and satellite observations at a summer monsoon coast ...... 172 Modelling extreme precipitation in the tropical South Pacific: A case study over New Caledonia ...... 173 Recent changes in mean and extreme temperature and rainfall in the western Pacific ...... 174 On the relationship between Indian Ocean Sea Surface Temperature Variability and in the Southwest Pacific ...... 175 Impact of low-frequency oscillations on rainfall in French Polynesia ...... 176 Effect of ENSO and IPO on rainfall in the Pacific Islands ...... 177 3.6 Modelling, prediction and projections of climate variability and change ...... 178 Preparing ACCESS for CMIP6 ...... 178 Earth System Model development under the Deep South National Science Challenge ...... 179 Preliminary results of the ACCESS-CM2 Pre-industrial Spin-up for CMIP6 Experiments ...... 180 Selecting a climate model subset to optimise key ensemble properties ...... 181

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What climate sensitivity measure is most useful for projections? ...... 182 Does ENSO change under anthropogenic forcing? ...... 183 On the choice of ensemble mean for estimating the forced signal in the presence of natural variability ...... 184 On the Improved Turbulent Kinetic Energy Spectrum in ACCESS via Stochastic Backscatter Injection ...... 185 Conceptual understanding of the large-scale hydrological cycle with a globally resolved energy balance model ...... 186 3.7 Decadal climate prediction session ...... 187 The CAFE EnKF system for coupled data assimilation and forecast initialisation in the seasonal to multi-year space ...... 187 Decadal climate predictability in the southern Indian Ocean captured by SINTEX-F using a simple SST-nudging scheme ...... 188 Model under-representation of decadal Pacific wind trends due to tropical Atlantic biases .... 189 Dynamical downscaling of CanSIPS climate forecasts over North America ...... 190 The CSIRO Climate Analysis Forecast Ensemble system ...... 191 Initialized decadal prediction for transition to positive phase of the Interdecadal Pacific Oscillation and resumption of larger rates of global warming ...... 192 Assessing the predictability of ENSO using historical climate forecasts from the CAFE system 193 On the dynamics of extreme rainfall in Tasmania ...... 194 Diagnosis of the extent of balance in the JRA-55 reanalysis via a normal mode function expansion ...... 195 Inter-basin sources for two-year predictability of the multi-year La Niña event in 2010-2012 . 196 3.8 Regional climate projections and applications ...... 197 Developing the Conformal Cubic Atmospheric model for CORDEX regional climate projections ...... 197 Can bias correction of regional climate model lateral boundary conditions improve low- frequency rainfall variability? ...... 198 Future climate projections for the Australian Alps ...... 199 Climate change projections and implications for decision making in the Wellington Region ... 200 Impact of CMIP5 SST biases on the South Pacific Convergence Zone response to climate warming ...... 201 South Atlantic Ocean precipitation associated with extratropical cyclones ...... 202 Integrating climate modelling into hydrological modelling at regional scale: a review of studies in Brazil ...... 203 Downscaling future climate scenarios to vineyard scale, examples from France and New Zealand ...... 204 Exploring the future change space for fire weather in southeast Australia ...... 205

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3.9 Climate extremes in a warmer world – detection and attribution and implications of global warming thresholds ...... 206 Exploring the scalability of a suite of extreme indices in the context of the Paris low-warming targets ...... 206 Evaluating simulated climate change in support of extreme weather event attribution ...... 207 Land use implications for climate extremes in low emission scenarios: Results from HAPPI-LAND ...... 208 Changing frequency of flooding in Bangladesh: Is the wettest place on Earth getting wetter? 209 Extreme rainfall in New Zealand and associated flooding events: using science to estimate attributable financial costs...... 210 Anthropogenic and natural influences on atmospheric circulation during heatwaves in Melbourne and Perth ...... 211

The effect of increasing CO2 on the extreme September 2016 rainfall across south eastern Australia ...... 212 Severe drought in southern Australia in a warming world ...... 213 3.10 Climate extremes and impacts ...... 214 Effects of climate variability and change on damaging hail risk ...... 214 Extreme rainfall characteristics in central-southern Chile and its relationship with atmospheric rivers ...... 215 What causes multi scaling relationships in extreme rainfalls? ...... 216 Changes in daily temperature extremes relative to the mean and their drivers in observations and CMIP5 models ...... 217 Global climate in 2017 ...... 218 Heatwave and heat-humidity index simulation skill in Australian cities with global climate models ...... 219 Recent and future changes of dry spells in Croatia ...... 220 tracking in a future climate ...... 221 Forewarned is forearmed: equipping farmers and agricultural value chains to proactively manage the impacts of extreme climate events ...... 222 Big data solutions for quantifying the costs of climate risk to new critical infrastructure ...... 223 Climate change and the international shipping trade ...... 224 3.11 Science supporting the Paris Agreement: Southern Hemisphere perspectives ...... 225 The global carbon budget and tracking the Paris Agreement ...... 225 The Carbon Dioxide Removal Model Intercomparison Project (CDR-MIP): Rationale and experimental design ...... 226 Australia’s Earth System Model: ACCESS-ESM ...... 227

Budgets of CO2, CH4 and N2O fluxes in the southern land and ocean ...... 228 Comparing data from the Australian greenhouse gas observation network with a high resolution model ...... 229

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Methane emissions through soil in coal seam gas development area, Queensland ...... 230

Quantification of urban CO2 emissions ...... 231 3.12 Processes, impacts and likelihood of severe droughts in the Southern Hemisphere ...... 232 Paleoclimate perspectives on historical and future drought risk in eastern Australia ...... 232 The 2010-2015 mega drought in Central Chile: Impacts on regional hydroclimate and vegetation ...... 233 Using instrumental, palaeoclimate, and climate model data to better understand what is plausible with respect to historical and future rainfall – a case study from the Lockyer Catchment, southeast Queensland, Australia ...... 234 Using reconstructions of winter and summer hydroclimate in western Tasmania ...... 235 The impact of ocean variability on tropical rainfall ...... 236 Correlation between drought indices and soil moisture data and their application for evaluation of drought characteristics ...... 237 3.13 Palaeoclimate reconstruction and modelling ...... 238 Sensitivity of Antarctica to ocean warming during the last interglacial ...... 238 Westerly wind variability at sub-Antarctic Macquarie Island: Links to the Southern Annular Mode and Southern Hemisphere temperature ...... 240

Abrupt early deglacial atmospheric CO2 increase driven by Southern Hemispheric westerlies 241 Using palaeoclimate data and models to detect climate and environmental tipping points in the Earth System ...... 242 From Antarctic ice cores to Australia’s climate: hydroclimate reconstructions using an alternative proxy ...... 243 New Millennial-length summer temperature reconstructions for southeastern Australia ...... 244 Pacific ENSO variability during the 13th to 15th centuries ...... 245 An extended record of Indian Ocean Dipole variability from Indonesian Corals ...... 246 Drivers of prolonged expansion and contraction periods of the Indo-Pacific tropical rain belt over the last millennium ...... 247 3.14 Data homogenisation and other statistical challenges in climatology ...... 248 Testing for collective significance of temperature trends ...... 248 Investigating Australian temperature distributions using record breaking statistics and quantile regression ...... 249 A fluctuation in surface temperature in historical context: reassessment and retrospective on the evidence ...... 250 The next-generation ACORN-SAT Australian temperature data set ...... 251 3.15 Climate – general ...... 252 Precipitation and land-atmosphere feedbacks control the uncertainty in how mid-latitude heat extremes intensify in the future ...... 252 Interdecadal Pacific Oscillation influences the timing of an ice-free Arctic Ocean ...... 253

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Compelling evidence for a very limited role of internal climate variability on global warming . 254 Climate sensitivity revisited ...... 256 3.16 Historical climatology in the Southern Hemisphere ...... 257 An Australian history of anthropogenic climate change ...... 257 Increasing Australia’s tide gauge records through data digitisation ...... 258 Learning from notorious maritime storms of the late 1800s ...... 259 Climate data rescue activities at Météo-France in the Southern Hemisphere ...... 260 Recovering historic Southern Ocean climate data using ships’ logbooks and citizen science ... 261 Theme 4: Weather ...... 262 4.1 A session in honour of Professor Ian H. Simmonds ...... 262 Atmospheric transport modelling and applications ...... 262 From one of the first objective cyclone tracking schemes to a unique frontal identification method ...... 263 How much does atmospheric frontal rainfall in Australia and New Zealand depend on SST frontal strength in the Indian and Southern Oceans? ...... 264 Recent trends and variability in global cyclones and anticyclones ...... 265 An analysis of Southern Hemisphere circulation over the last millennium ...... 266 Variability in planetary wave activity over the 20th century ...... 267 It’s just not cricket! ...... 268 If that’s correct, we'll win a Nobel Prize! Being healthily sceptical with common or garden variety climate indices ...... 269 4.2 High impact weather in research and operations ...... 270 South East Queensland hazard analysis and verification testbed – operations and preliminary results ...... 270 Simulated changes in supercell thunderstorms crossing a sea breeze front ...... 271 Subtropical heat waves in the Brisbane-region of Australia ...... 272 Bayesian statistical approach for developing a convective windstorm climatology of Australia ...... 273 New developments in the Bureau’s thunderstorm prediction system – Calibrated Thunder ... 274 Floods in the South Island of New Zealand: the importance of atmospheric rivers ...... 275 Simulations of the Black-Saturday Kilmore East Wildfires with the Unified Model ...... 276 The rainfall mechanism analysis of Tropical cyclone Oswald(2013) ...... 277 Improved extreme weather hazard prediction and communication through science to operations ...... 278 Improvements in the detection and prediction of volcanic ash for aviation at the Bureau of Meteorology ...... 279 Synoptic and sub‐synoptic‐scale features associated with extreme surface gusts during the Adelaide Storm of September 2016...... 280

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Probabilistic forecast of cyclone-induced hazards within SPICy project ...... 281 High-Resolution Rainfall and Hydrological Ensemble Forecasts during the passage of Intense Tropical Cyclone Bejisa (2014) over Reunion Island (SWIO) ...... 282 A parametric model for hailstorm development at southeast Australia ...... 283 Multi-week tropical cyclone prediction in ACCESS-S1 and the role of the MJO ...... 284 Objective reanalysis of Tropical Cyclone wind radii parameters using the Deviation Angle Variance Technique...... 285 High-impact severe thunderstorm events in southeast Queensland ...... 286 4.3 Special session on renewable energy – the effects of weather and climate on integrating renewables into our energy industry ...... 287 Mathematical and statistical tools for energy meteorology ...... 287 Evaluation and improvement of solar irradiance forecasting skills of the Australian Bureau of Meteorology’s ACCESS models ...... 288 Assessment of solar irradiance predictions using WRF on days of high intermittency ...... 289 Wind resource assessment for Tahiti, French Polynesia ...... 290 Where should new wind energy sites be located to avoid climate and financial risk? ...... 291 Bureau of Meteorology data and services for renewable energy industry and research ...... 292 4.5 East coast lows – drivers of variability and associated extremes ...... 293 A physically-based classification of east coast lows ...... 293 East Coast Lows – classification and terminology used by the New South Wales RFC ...... 294 Reassessing "objective" databases of ECLs using satellite data ...... 295 Wave direction and spatial variability in coastal erosion due to east coast lows: high-resolution observations from the June 2016 event ...... 296 4.6 Impact and risk assessment for weather extremes ...... 297 Towards a consistent global database of tropical cyclone risk ...... 297 A new world of extreme weather ...... 298 The Melbourne thunderstorm asthma epidemic of 21 November 2016 ...... 299 Exploring unseen disaster scenarios: interrogating stochastic tropical cyclone event catalogues for hazard and impact assessment ...... 300 A global investigation of the impacts of landfalling tropical cyclones on societies ...... 301 Tropical cyclone Debbie: investigation of building performace (wind loads, wind driven rain and storm surge) ...... 302 Quantitative modelling of vulnerability to severe wind ...... 303 Impact-based forecasting in the coastal zone: East Coast Lows ...... 304 4.7 Weather – general ...... 305 The continued development of the Bureau of Meteorology’s Numerical Weather Prediction Systems ...... 305 Forecasting rainfall over the Mount Lofty Ranges, challenges and downscaling methods ...... 306

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A high-level framework for assessing the relative performance of two forecast sources ...... 307 Theme 5: Land surface processes ...... 308 5.1 Urban climate ...... 308 How "hot" is too hot? Evaluating acceptable ranges of outdoor thermal comfort in an equatorial urban park ...... 308 Mitigation of Urban Heat Island in the city of Melbourne: Green and Cool Roofs Strategies ... 309 A mixed physical/statistical city-scale energy demand model for Australia ...... 310 Validation of high resolution Met Office Unified Model over Singapore and analysis of its impacts on local and regional climate ...... 311 Contribution of surface urban heat island to summer heat waves – a case study of Sydney, Australia ...... 312 Using urban irrigation and cool roofs to mitigate future heatwaves ...... 313 5.3 Land surface processes – general ...... 314 Vegetation responses to extreme wetting and drying events in central Australia using combined satellite and flux tower observations ...... 314 Vegetation Disturbance and Recovery: Importance for decadal prediction ...... 315 Is there a "speed bias" in eddy-covariance measurements at a fixed location? ...... 316 Derived Optimal Linear Combination Evapotranspiration (DOLCE): a global gridded synthesis et estimate ...... 317 Optimising Weather Research Forecast model performance by land-use change in the Southwest Western Australia ...... 318 Theme 6: Antarctic Science and cryosphere ...... 319 6.1 Antarctic : variability, trends, and drivers ...... 319 Antarctic sea ice variability and associated changes in Southern Ocean cyclones and large-scale drivers ...... 319 Process-informed modelling of the sea ice floe size distribution ...... 320 Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability ...... 321 Southern Hemisphere surface climate and ocean circulation response to Antarctic meltwater in a warming world ...... 322 On the role of the tropical Indian Ocean for the sharp decline of Antarctic Sea-Ice in austral spring 2016 ...... 323 The highest temperature for the Antarctic continent: 1 Local-scale phenomena triggered by large-scale forcing ...... 324 6.4 Antarctic science ...... 325 Atmospheric influences on the anomalous 2016 Antarctic sea ice retreat ...... 325 Large-scale forcing of the Amundsen Sea low and its influence on sea ice and west Antarctic temperature ...... 326

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Studying green and blue icebergs of marine ice to better understand ice-shelf basal processes ...... 327 Ocean-sea ice interactions in the Southern Ocean in CMIP5 models ...... 328 Future projections of Antarctic ice shelf melting ...... 329 Ablation of sloping ice-shelf at Antarctic Conditions ...... 330 Theme 7: Climate services and Community engagement ...... 331 7.1 Weather and climate in the media AND 7.2 Education and outreach ...... 331 Cutting to the Chase: Climate Change Communication...... 331 Observing and Predicting the 2015-16 El Niño ...... 332 Communicating links between climate change and extremes ...... 333 An analysis of climate and weather in the media ...... 334 Comparing weather prediction information between formal and informal sources ...... 335 Bearing witness 2017: Fiji climate change journalism revisited ...... 336 Newspaper coverage of climate change in Fiji: a content analysis ...... 337 Life cycle assessment in interdisciplinary education of sustainability, energy and green economics ...... 338 Researcher development in the ARC Centre of Excellence for Climate Extremes ...... 339 The Sydney Schools Weather and Air Quality (SWAQ) Network ...... 340 How leadership skills can help us become better scientists: Lessons from Antarctica ...... 341 Ambassadors for science ...... 342 7.3 Climate services for decision makers ...... 343 The high value and short payoff time of seasonal forecasts in risk-averse crop management . 343 Seasonal climate outlooks: keeping the customer satisfied ...... 344 Climate Change Services: online tools that meet the needs of users…or not: Climate Change in Australia User Surveys 2016 - 2017 ...... 345 Useful and usable information delivery for coastal adaptation ...... 346 NextGen Projections: planning for the next generation of national climate projections in Australia ...... 347

xiv www.csiro.au Plenary Sessions Climate change science and solutions for Australia and our region Cleugh, Helen1 1Climate Science Centre, CSIRO

Plenary – RH Clarke Lecture – February 5, 2018, 0945-1030

With one of the most variable in the world, Australian research has long played a key role in helping Australians manage climate risk and its impact on our environment, economy and communities. Our research and observations also show that Australia’s already variable climate is changing: old patterns are shifting, records are being broken, and the past is no longer a reliable guide to the future.

Global climate simulations and regional projections are therefore needed to provide a view of Australia’s future climate and likely impacts; yet significant knowledge gaps and uncertainties remain in our climate simulation capabilities. New understanding and insights are needed just as much today as in the past for Australia, and our broader region, to be prepared and resilient in the face of climate and environmental change. Moreover, effective adaptation and mitigation actions to stabilize the global climate, as committed to in the Paris 2015 Agreement, will require robust science, objective analyses, and highly credible climate information that is relevant to our region.

The Climate Science Centre was established by CSIRO in 2016 to ensure that Australia has the world- class science capability needed to address these needs, and deliver national benefit. Building on the very strong research foundation of its predecessors, the Centre has a focus on science excellence, collaboration and partnerships, and solutions – so that policy and management decisions in Australia are effectively informed by the best climate system science.

This talk will describe the Climate Science Centre – especially its current and future research goals and priorities. In describing these goals and priorities, I will reflect on what has been achieved and what research gaps remain a priority. I will also describe our vision for more effectively connecting adaptation and mitigation solutions to climate system science (modelling, observations and process studies). This is critically important to enabling Australasia to be better prepared for, and resilient to, environmental and climate change; but will also require effective collaboration and partnerships within CSIRO, with the Bureau of Meteorology and Australian universities, and globally.

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Drivers of recent oceanic trends around Antarctica from the surface to the abyss England, Matthew H.1 1UNSW Climate Change Research Centre (CCRC)

Plenary – February 5, 2018, 1400-1445

Despite unequivocal global warming, Southern Ocean surface waters have largely cooled over the past ~40 years and Antarctic sea ice has expanded, in stark contrast to almost all historical CMIP5 model simulations. The Southern Ocean surface cooling is nearly circumpolar, except notably in the Amundsen-Bellingshausen Sea, where rapid warming and sea-ice retreat has been observed. In contrast to the overall surface cooling around Antarctica, subsurface ocean warming has been observed, both over the Antarctic shelf and in the abyssal ocean layers ventilated by Antarctic Bottom Water. The shelf water warming threatens to drive catastrophic retreat of Antarctica’s marine- terminating ice sheets, resulting in accelerated global sea-level rise. The bottom water warming likely indicates a slowdown of the overturning of dense water around Antarctica, with implications for the global cycling of heat and nutrients by the oceans. This talk will present an overview of the processes that have led to these oceanic temperature trends around Antarctica, and give an outlook of expected changes over the coming decades.

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The 2018 Tinker-Muse Prize for Science and Policy in Antarctica

The “Tinker-Muse Prize for Science and Policy in Antarctica” is a USD $100,000 unrestricted award presented to an individual in the fields of Antarctic science and/or policy who has demonstrated potential for sustained and significant contributions that will enhance the understanding and/or preservation of Antarctica. The Prize is inspired by Martha T. Muse’s passion for Antarctica and is a legacy of the International Polar Year 2007-2008.

The prize-winner can be from any country and work in any field of Antarctic science and/or policy. The goal is to provide recognition of the important work being done by the individual and to call attention to the significance of understanding Antarctica in a time of change. A website with further details, including the process of nomination, closing date and selection of the Prize recipients, is available at www.museprize.org.

The Prize is awarded by the Tinker Foundation and administered by the

Scientific Committee on Antarctic Research (SCAR).

Nominations open until

14 March 2018

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Natural drivers of interannual to decadal variations in surface climate Maher, Nicola1,2

1Max-Planck Institude for Meteorology, Hamburg, Germany 2Alexander von Humboldt Foundation, Germany

Plenary – Uwe Radok Award – February 6, 2018, 1400-1430

Hiatus periods are defined as decades where the surface of the Earth does not warm, despite continued anthropogenic greenhouse gas emissions, while accelerated warming refers to decadal periods where the SAT warms faster than expected. My PhD thesis aims to understand drivers of fluctuations in surface climate that could result in such periods, specifically focusing on natural variability in the Indo-Pacific region and the role of volcanism.

Drivers of decadal hiatus periods in the Coupled Model Intercomparison Project (CMIP5) coupled climate models are examined. Hiatus periods are identified in three categories, (i) those due to volcanic eruptions, (ii) those associated with negative phases of the Interdecadal Pacific Oscillation (IPO), where accelerated warming is associated with the IPO positive phase, and (iii) those affected by anthropogenic aerosols in the mid 20th Century. The likelihood of future hiatus periods is shown to be sensitive to the rate of change of anthropogenic forcing and the influence of volcanism.

Large volcanic eruptions are also found to influence tropical Indo-Pacific variability. We demonstrate a significant increase in the likelihood of co-occurring El Niño and positive Indian Ocean Dipole events in the austral spring/summer post-eruption. There is also an increase in the chance of a La Niña event occurring in the third austral summer post-eruption. Combined with the initial aerosol- induced cooling, the delayed La Niña-like response may increase the persistence of the multi-year cooling of global surface temperature post eruption.

To further investigate the role of the IPO in driving the recent hiatus, we perform sensitivity experiments in an eddy permitting model. The recent negative phase of the IPO is associated with a trade wind intensification in the Pacific. A global ocean model forced with an atmospheric state, which trends to match observational fields, reveals an increase in heat content in both the Indian and Pacific Oceans. This is due to increased heat flux into the Pacific Ocean and increased transport of heat from the Pacific to the Indian Ocean associated with an increase in the Indonesian throughflow. This increased uptake of heat into the sub-surface Indo-Pacific shows that the ocean continues to warm, despite the surface cooling associated with the hiatus.

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Global warming and coral reefs Hughes, Terry P.1 1Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies, James Cook University

Plenary – February 7, 2018, 0845-0930

Tropical reef systems are increasingly threatened by global warming, especially by heatwaves that , bleach and often kill corals. Increasingly we are transitioning to a new era in which the interval between recurrent bouts of coral bleaching is too short for a full recovery of mature assemblages. Throughout the tropics, the median return-time between pairs of severe bleaching events has diminished steadily since 1980, and is now only six years. As global warming has progressed, tropical sea surface temperatures are warmer now during current La Niña conditions than they were in El Niño events three decades ago. Consequently, as we transition to the Anthropocene, coral bleaching is occurring more frequently in all El Niño Southern Oscillation phases, increasing the likelihood of annual bleaching in coming decades. A case study is the Great Barrier Reef, which has now bleached four times since 1998, including the unprecedented back-to-back bleaching in 2016 and 2017 that has transformed the ecology of the world’s largest reef system.

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Tropical cyclones and the global energy budget: their role and implications Holland, Greg1, Prein, Andreas1, Bruyere, Cindy1 1Capacity Center for Weather and Climate Extremes, NCAR

Plenary – February 8, 2018, 0845-0930

The bulk of the tropics are clear of clouds and continuously cool at a rate of 1-2oC per day and thermodynamic balance requires a vertical transport of moist enthalpy from the surface. In a landmark paper, Riehl and Malkus (1958) showed that tropical convection, or ‘Hot Towers’, provided a crucial vertical link in the maintenance of this tropical energy balance. A number of further studies have confirmed the link and updated the actual contribution of tropical convection.

Here we examine the relative roles of tropical cyclones compared to sustained active regions (such as the Indonesian Maritime Continent and the intertropical convergence zone), and other transient systems in maintaining this heat balance. We find that moist vertical motion in tropical cyclones is a major contributor, providing around 40% of the total required to maintain overall balance. As cyclones move away from the tropics and pass through the descending branch of the Hadley circulation, an interesting transformation occurs. The net vertical energy transport drops temporarily then returns towards previous levels, except now the bulk of the energy export is directed towards subtropical regions.

The implications of these findings for tropical cyclone activity in both current and future climate will be discussed.

Riehl, H., and J. Malkus, 1958: On the heat balance in the equatorial trough zone. Geophysica, 6, 503– 538.

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Characterizing benefits of mitigation and avoided impacts, especially in the context of the Paris warming targets Tebaldi, Claudia1 1Climate and Global Dynamics laboratory at the National Center for Atmospheric Research

Plenary – February 8, 2018, 1405-1445

I will present some highlights from a series of studies that were recently conducted at NCAR within the erstwhile Climate and Human System Project, as part of two collections surveying “Benefits of Reduced Anthropogenic Climate change”: BRACE and BRACE 1.5.

We rely on a set of large initial condition ensembles run with NCAR-DOE’s CESM. The different ensembles explore climate outcomes under RCP8.5, RCP4.5 and three newly designed low-warming pathways addressing specifically the Paris targets of 1.5C and 2.0C global warming above preindustrial. The availability of large ensembles allows us to explore differences in the presence of internal variability, addressing the significance of these differences even when comparing trajectories differing by small global average temperature differentials.

The studies within BRACE and BRACE1.5 address avoided impacts both within the physical climate system and within natural and human systems (e.g., heat and precipitation extremes, agricultural yields, human health, tropical cyclone damages). I will present some of the highlights, focusing on two specific topics: changes in heat extremes and changes in expected crop yields. Besides exploring very different outcomes, obviously, these two analyses also differ in the significance of their results, and the level of uncertainty affecting them, offering a good starting point for a reflection upon the challenges we face in quantifying benefits of mitigation to inform policy decisions.

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Communicating science Schmidt, Gavin A.1 1Goddard Institute for Space Studies, NASA

Plenary – February 9, 2018, 0845-0930

We all know that communicating our science is hard, but we also know that it is necessary. I will discuss some of the narrative techniques that have worked, and some of the times when it all went horribly wrong. While there will always be people who will distort and politicize our results, many of the worst examples of miscommunications don’t involve them directly. I will try and show that we can all do a lot better to reduce confusion and help people make more informed decisions. This talk will also include nice animations.

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Theme 1: Oceanographic Processes and Observations 1.1 Variability and change in the Indo-Pacific and Australian regional seas – A session in honour of Gary Meyers

Gary Meyers – A scientific life well lived Ridgway, Ken1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, TAS, Australia

Session 1.1 – February 8, 2018, 0930-0945

This presentation we describe some of the many and varied scientific achievements of Gary Meyers. Firstly Gary is recognized for the excellence of his science. His research interests included baroclinic Rossby waves, variability of the Indian Ocean, its relationship to El Nino Southern Oscillation, Indonesian throughflow and the design of observing networks. The talk includes highlights of his published work in these fields. Secondly, we present aspects of his longstanding contributions to developing and maintaining global ocean observing programs. From his early career involvement in the Pacific sea level network with Klaus Wyrtki, he is perhaps best known for his efforts to develop global ocean-observing using the expendable bathy-thermograph (XBT) launched from a volunteer- fleet of merchant vessels to observe subsurface oceanic temperature. Within Australia he was the founding director of the Integrated Marine Observing System. He had a particular interest in expanding understanding of the oceanography of the Indian Ocean through an expansion of observations in the region. Gary demonstrated scientific leadership both nationally and internationally by his involvement in many scientific panels and committees, including TOGA, WOCE, CLIVAR and GOOS. We present some of the significant impacts of these involvements. Nationally he promoted and initiated development of the model (POAMA) to predict seasonal climate in Australia. Also in collaboration with BoM and the Royal Australian Navy he promoted and initiated the model (Bluelink) to provide detailed maps of oceanic structure around Australia. Finally, Gary collaborated with many colleagues around the world and was a mentor and advisor to many students from a variety of backgrounds. The presentation includes contributions from just a few of this group describing the impact and influence on their careers.

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Progress in understanding and predicting the IOD and its impacts Hendon, Harry1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Melbourne, Australia

Session 1.1 – February 8, 2018, 0945-1000

Progress in understanding and predicting the IOD and its impacts, especially for Australian climate, are reviewed. My interest in the IOD began with the Western Australian Marine Science Institution project 2006-2011, for which Gary Meyers was the original node leader. In that program, we assessed the capability to simulate and predict the IOD and its impacts on the WA marine environment using the BoM first generation coupled model seasonal prediction system. Recent progress in simulating and predicting the IOD and understanding of the mechanism of its impact on Australian climate and more generally the extratropics of the Southern Hemisphere is reviewed. The interaction of the IOD with ENSO is also reviewed, highlighting the important driving role of the IOD for development of La Nina in 2016.

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Mean subsurface upwelling induced by intraseasonal variability in the equatorial Indian Ocean Masumoto, Yukio1,2, Ogata, Tomomichi2, Nagura, Motoki2

Presenting author’s e-mail: [email protected]

1University of Tokyo, Tokyo, Japan 2Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan

Session 1.1 – February 8, 2018, 1000-1015

A possible formation mechanism of mean subsurface upwelling along the equator in the Indian Ocean is investigated using a series of hierarchical setting of ocean general circulation model (OGCM) integrations and analytical considerations. In an eddy-resolving OGCM with realistic forcing, mean vertical velocity in the tropical Indian Ocean shows rather strong upwelling, with its maximum on the equator in subsurface layer below the thermocline. A heat budget analysis exhibits that horizontal and vertical heat advection due to currents and temperature deviations from the mean balances with vertical advection due to mean equatorial upwelling. Horizontal heat convergence is mostly associated with intraseasonal variability with a period from 3- to 91-day, while contribution from longer period (> 91 days) is small. Sensitivity experiments with a coarse-resolution OGCM further demonstrate that such mean equatorial upwelling cannot be reproduced by seasonal forcing only. Adding the intraseasonal wind forcing, especially meridional wind variability with a period of 15 days, generates significant mean subsurface upwelling on the equator. Further experiments with idealized settings confirm the importance of intraseasonal mixed Rossby-gravity (MRG) waves to generate mean upwelling, which appears along the energy “beam” of the MRG wave. An analytical solution of the MRG indicates that wave-induced temperature advection caused by the MRG waves with upward (downward) phase propagation results in warming (cooling) on the equator. This wave- induced warming (cooling) is shown to balance with the mean equatorial upwelling (downwelling), which is consistent with simulated characteristics in the OGCM experiments.

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Interannual variability of the Indonesian Throughflow transport: a revisit based on 30-year expendable bathythermograph data Liu, Qin-Yan1,2, Feng, Ming2, Wang, Dongxiao1, Wijffels, Susan3

Presenting author’s e-mail: [email protected]

1South China Sea Institute of Oceanology, CAS, Guangzhou, China 2CSIRO Oceans and Atmosphere, Floreat, Western Australia, Australia 3CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia

Session 1.1 – February 8, 2018, 1015-1030

Based on 30-year repeated expendable bathythermograph (XBT) deployments between Fremantle, Western Australia and the Sunda Strait, Indonesia from 1984 to 2013, interannual variability of geostrophic transport of the Indonesian Throughflow (ITF) and its relationships with El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are investigated. The IOD induced coastal Kelvin waves propagate along the Sumatra-Java coast of Indonesia, and ENSO induced coastal Kelvin waves propagate along the northwest coast of Australia, both influencing interannual variations of the ITF transport. The ITF geostrophic transport is stronger during La Niña phase and weaker during El Niño phase, with the Niño3.4 index leading the ITF variability by 7 months. The Indian Ocean wind variability associated with the IOD to a certain extent offset the Pacific ENSO influences on the ITF geostrophic transport during the developing and mature phases of El Niño and La Niña, due to the co-varying IOD variability with ENSO. The ITF geostrophic transport experiences a strengthening trend of about 1 Sv every 10 years over the study period, which is mostly due to a response to the strengthening of the trade winds in the Pacific during the climate change hiatus period. Decadal variations of the temperature-salinity relationships need to be considered when estimating the geostrophic transport of the ITF using XBT data.

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Potential Origins of Pacific Decadal Variability Zeller, Mathias1,2, McGregor, Shayne1,2, Spence, Paul2,3

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia 2ARC Centre of Excellence for Climate System Science, Australia 3University of New South Wales, NSW, Australia

Session 1.1 – February 8, 2018, 1100-1115

Our study focuses on the shallow overturning circulation in the Pacific Ocean, known as the subtropical cells (STCs). The STCs extend from the tropics to the subtropics in both hemispheres and are thought to modulate the background state that the El Nino – Southern Oscillation (ENSO) operates in. This background state modulation is important as it impacts the frequency and intensity of ENSO events along with its teleconnections. Therefore, understanding what drives STC variability and exactly how it modifies the tropical Pacific mean state would be a big step towards better understanding Pacific Ocean decadal variability and its predictability. We use a high-resolution ocean general circulation model to investigate the transports that are associated with the STC branches along 5ºN and 5ºS. Based on a simulation driven by atmospheric re-analysis, we find that the Southern hemisphere (SH) STC has similar variability to the Northern hemisphere (NH) STC, however, the NH STC appears to lead the SH STC by 5 months (lagged corr: 0.73). We next investigate the mechanisms driving the STC variability and ask how much ENSO itself can drive the modelled STC variability. Therefore, winds that are linearly and non-linearly related to ENSO are identified and used to force the ocean model. Firstly, we find that the winds associated with ENSO itself can explain 50% of the STC variability, including the hemispheric differences consistent with the full simulation, which suggests a prominent role for ENSO in modulating its own background state. Secondly, we find that it is the winds that are non-linearly related to ENSO that cause the change in the phase relationship between the NH and SH STCs. We then further explore the winds responsible for generating the remaining 50% of STC variability.

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Evidence of a super-convergence zone in the subtropical Indo-Pacific Ocean Maes, Christophe1, Grima, Nicolas1, Blanke, Bruno1, Martinez, Elodie2, Paviet-Salomon, Thomas1, Huck, Thierry1

Presenting author’s e-mail: [email protected]

1Laboratoire d’Océanographie Physique et Spatiale, Ifremer, CNRS, IRD, IUEM, Univ. Brest, Brest, France 2Ecosystèmes Insulaires Océaniens-IRD, Tahiti, French Polynesia

Session 1.1 – February 8, 2018, 1115-1130

In order to study the dynamics of marine debris at global scales, a non-stationary solution of particle trajectories based on Lagrangian diagnostics combined with an ocean reanalysis of surface currents is explored over the period 1985-2013. The methodology is based on determining the forward evolution of an initially homogeneous array of particles located on each grid point of the model (1/4° resolution). Results exhibit the relatively well-known five main convergence zones of surface aggregation, located in the subtropical regions and maintained by converging Ekman currents. However, two important differences relative to the present knowledge of these zones are evidenced by our analysis. First, the central position of the convergence zone in the south Indian Ocean is located in the eastern part of the basin, a displacement toward the East larger than 40° in longitude while its position in latitude remains similar (near 30°S). Second, in the Indo-Pacific Ocean, the present analysis reveals, for the first time, the permanent presence of a convergent dynamics connecting the south Indian and Pacific zones through the Great Australian Bight, the Tasman Sea and the southwestern region of the Pacific Ocean. Like the “super-gyre” that connects the thermocline waters of the subtropical gyres of the South Pacific, Indian, and South Atlantic Oceans, this surface “super-convergent” route connects the cores of the convergence zones of the Indian and Pacific Ocean. At timescales longer than 20-yr the results show a slow decrease in the accumulation rate of particles in the southeastern part of the Indian Ocean, while the concentration in the south Pacific region is still increasing after 29 years. By way of comparison, the rates in the three other convergence zones are stabilized after a 10-yr period. Implications for the dispersion of the marine litter and debris will be briefly discussed.

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Northern boundary circulation properties of the South Australian Current System based on a gridded hydrography Duran, Earl R.1,2, Phillips, Helen E.1,3, Furue, Ryo4, Spence, Paul1,2, Bindoff, Nathan1,3,5,6

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre (CCRC), Sydney New South Wales, Australia 2ARC Centre of Excellence for Climate System Science (ARC CSS), Australia 3Institute for Marine and Antarctic Studies (IMAS), Hobart Tasmania, Australia 4Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama Kanagawa, Japan 5Antarctic Climate & Ecosystems Cooperative Research Centre (ACE CRC), Hobart Tasmania, Australia 6Commonwealth Scientific and Industrial Research Organisation (CSIRO), Hobart Tasmania, Australia

Session 1.1 – February 8, 2018, 1130-1145

The southern continental margin of Australia hosts a unique northern boundary circulation which transports waters essentially zonally between Cape Leeuwin, the southwest corner of mainland Australia, and South East Cape, the southern tip of Tasmania, whereas other major boundary currents typically transport water meridionally.

This study builds on Furue 2017’s work on the Leeuwin Current System (LCS) along western Australia. We carry an analysis of the regional boundary currents this time focusing on the whole northern boundary domain south of Australia. We propose to name the circulation in this domain, comprising the Coastal Currents (CC), the Shelf Break Currents (SBC, Leeuwin Current + South Australian Current + Zeehan Current), the Flinders Current and the Onshore Flows, the South Australian Current System (SACS).

We provide for the first time a comprehensive observational study of the mean and seasonal variability of the currents. Specifically, we describe the spatio-temporal changes in the (i) the eastward and westward evolution of the SBC and FC transport respectively (ii) the continuity of the SBC (iii) the horizontal and vertical exchanges between the SBC and FC and (iv) the coastal and onshore horizontal contributions from the CC and the OF respectively. We also check some of the theory provided in the idealised OCCAM experiments from Middleton and Cirano 2002 and Cirano and Middleton 2004 on the downwelling shelf break flows, northward Sverdrup transport and the FC westward intensification.

We use the "aus8" version of the gridded hydrographic climatology CSIRO Atlas of Regional Seas (CARS) data which provides a 1/8^th degree resolution of CARS, a grid scale fine enough to resolve small-scale boundary currents. This analysis is supported by a comparison with KDS75, a 1/10^th degree version of MOM5 forced by the CORE cNYF2 climatology.

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Building on the legacy of Gary Meyers, inaugural director of Australia’s Integrated Marine Observing System (IMOS) Moltmann, Tim1

Presenting author’s e-mail: [email protected]

1Integrated Marine Observing System (IMOS), University of Tasmania, TAS, Australia

Session 1.1 – February 8, 2018, 1145-1200

In May 2006, the Australian Government committed $50 million over five years to establish an Integrated Marine Observing System (IMOS). IMOS was conceived as a nation-wide, collaborative program, designed to observe the oceans around Australia, including the Indo-Pacific and Australian regional seas. Its mission is to provide data-streams in support of research on many of the critical marine issues facing Australia. Dr Gary Myers was selected as the inaugural Director of IMOS, taking up the job in early 2007. As an eminent oceanographer at the CSIRO in Hobart, and with a long interest in ocean observations, he was an excellent choice. Gary led the program through its formative stage, putting it on a stable base that continues to serve a large science community to this day. He retired in June 2009 having been instrumental in securing an additional $52 million investment to grow the program by 80% and extend it for a further two years. IMOS is now in its twelfth year of operation, and well on the way to a second decade of observing the ocean around Australia. This talk will provide an overview of the history and achievements of IMOS, with particular emphasis on the principles Gary instilled as the inaugural Director - societal benefit, open data access, international collaboration, and sustained observation. These principles remain highly relevant today, underpinning a high level of impact over the last decade, and positioning integrated marine observing to play an increasingly important role in driving the development of Australia’s blue economy.

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A decade of Integrated Marine Observing (imos) in Western Australia: Legacy and vision of Gary Meyers Pattiaratchi, Charitha1, D’Adamo, Nick2, Feng, Ming3, Kendrick, Gary4, McCauley, Robert5, Partridge, Julian4, Antoine, David4, Cosoli, Simone1

Presenting author’s e-mail: [email protected]

1School of Civil, Environmental and Mining Engineering & The UWA Oceans Institute, The University of Western Australia, Perth, Australia 2Intergovernmental Oceanographic Commission, Perth Program Office, Perth, Australia 3CSIRO 4School of Biological Sciences & The UWA Oceans Institute, The University of Western Australia, Perth, Australia

Session 1.1 – February 8, 2018, 1200-1215

West Australian Integrated Marine Observation System (WAIMOS) was set up as a node of the Integrated Marine Observation System (IMOS) since its inception under the leadership of Gary Myers. The main the main area of interest for WAIMOS is the continental shelf and slope regions offshore Fremantle extending northwards to Jurien Bay. Within this region there important topographic features such as the Rottnest Island and Perth Canyon and the circulation is dominated by the southward flowing Leeuwin Current (LC) the wind driven Capes Current (CC) located on the shelf. The IMOS infrastructure located in this region includes HF Radar (CODAR and WERA systems; Ocean gliders (Slocum and Seagliders); continental shelf moorings (ADCP, thermistor and water quality loggers); passive acoustic sensors; and, remotely sensed data products (SST and ocean colour). Example data collected from these instruments will be presented through the integration of different data sets, in relation to the understanding of different processes operating in the region and the advanced made in the past decade. These include: (1) Interaction between the LC and CC. Here, the warmer, lower salinity southward flowing Leeuwin Current interacts with the cooler, higher saline northward flowing Capes Current creates a region of high horizontal shear and thus intense mixing and the generation of eddies; (2) cascade of dense water along the continental shelf. The region experiences a Mediterranean climate with hot summers and cold winters. During the summer months the inner continental shelf waters increases in salinity due to evaporation. In winter as this higher salinity waters cool its density is higher than offshore waters and a gravitational circulation is set-up where the inner shelf water are transported as higher salinity plumes into deeper waters.

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Extreme marine warming across tropical Australia during austral summer 2015- 2016 Benthuysen, Jessica A.1, Oliver, Eric C. J.2,3, Feng, Ming4,5, Marshall, Andrew6

Presenting author’s e-mail: [email protected]

1Australian Institute of Marine Science, Townsville, Australia. 2Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia. 3ARC Centre of Excellence for Climate System Science, Sydney, Australia. 4CSIRO Oceans and Atmosphere, Indian Ocean Marine Research Centre, Crawley, Australia. 5Centre for Southern Hemisphere Oceans Research, Hobart, Australia. 6Australian Bureau of Meteorology, Hobart, Australia.

Session 1.1 – February 8, 2018, 1215-1230

During austral summer 2015-2016, widespread coral bleaching was reported from the Australian Northwest Shelf to the Central Great Barrier Reef, including severe coral bleaching and mortality throughout the Northern Great Barrier Reef. These events occurred during a marine heatwave that extended across tropical Australia’s marine waters from the Indian Ocean to the Coral Sea. We seek to understand the relative roles of drivers governing interannual and intraseasonal variability during the events that transpired. The marine heatwave was instigated by the strong El Niño due to enhanced solar radiation and reduced evaporative cooling. A marine heatwave framework is applied to daily sea surface temperatures, revealing warm anomalies emerging in the Indonesian-Australian Basin in late spring 2015 and in the Gulf of Carpentaria and the Northern Great Barrier Reef by January 2016. Peak temperature anomalies occurred in March 2016, exceeding 2°C above seasonal average temperatures over a broad spatial extent. In addition, observations are synthesised from in-situ deep-water and shelf temperature measurements, including Argo floats, shipboard thermosalinograph data, Slocum gliders, moorings, and temperature loggers. A data-assimilating model reveals changes in the upper ocean circulation and mixed layer depths consistent with El Niño events. Recommendations are made for future monitoring of marine heatwave events in this region.

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1.2 Physical oceanography in the Southern Ocean and at the Antarctic margins Convection in the Southern Ocean – What controls it? Behrens, Erik1, Rickard, Graham1

Presenting author’s e-mail: [email protected]

1National Institute for Water and Atmospheric Research, Wellington, New Zealand

Session 1.2 – February 6, 2018, 0930-0945

Open ocean convection (“convection”) in the Southern Ocean has not been observed since the mid- 1970s. However, coupled and forced simulations show an occurrence of these events in the Southern Ocean on various time and spatial scales with drastic implications for sea ice and heat content. We present results of an extensive sensitivity study of non-eddy resolving and eddy permitting global forced simulations. The sensitivity studies consider changes in the surface freshwater forcing, heat content management of Circumpolar Deep Water, vertical mixing and surface heat flux variations, as well as the parameterisation of mesoscale eddies. Results show that freshwater forcing affects directly surface stratification and thus the occurrence and intensity of convection. It will be demonstrated that brine rejection as a consequence of sea ice growth and thus stratification during winter season is a potential critical trigger for convection. Furthermore, we will show that increased vertical mixing leads to postponed onset of deep convection but not to a reduction as other studies have suggested. Mesoscale eddies reduce convection, since they tend increase the surface stratification.

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Impacts of broad-scale surface freshening of the Southern Ocean in a coupled climate model Purich, Ariaan1,2,3, England, Matthew H.2,3, Cai, Wenju1, Sullivan, Arnold1, Durack, Paul J.4

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Aspendale, Victoria 3195, Australia 2Climate Change Research Centre, University of New South Wales, Sydney, New South Wales 2052, Australia 3ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales 2052, Australia 4Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, California 94550, USA

Session 1.2 – February 6, 2018, 0945-1000

The Southern Ocean surface has freshened in recent decades, increasing water column stability and reducing upwelling of warmer subsurface waters. The majority of CMIP5 models underestimate or fail to capture this historical surface freshening, yet little is known about the impact of this model bias on regional ocean circulation and hydrography. Here we perform experiments using a global coupled climate model with additional freshwater applied to the Southern Ocean to assess the influence of recent surface freshening. The simulations explore the impact of persistent and long-term broad-scale freshening due to precipitation minus evaporation changes. Thus, unlike previous studies, the freshening is applied as far north as 55°S, beyond the Antarctic ice margin. We find that imposing a large-scale surface freshening causes a surface cooling and sea-ice increase under pre-industrial conditions, due to a reduction in ocean convection and weakened entrainment of warm subsurface waters into the surface ocean. This is consistent with inter-model relationships between CMIP5 models and our simulations, which suggest that models with larger surface freshening also exhibit stronger surface cooling and increased sea ice. Additional experiments are conducted with surface salinity restoration applied to capture observed regional salinity trends. Remarkably, without any mechanical wind trend forcing, these simulations accurately represent the spatial pattern of observed surface temperature and sea-ice trends around Antarctica. This study highlights the importance of accurately simulating changes in Southern Ocean salinity to capture changes in ocean circulation, sea surface temperature and sea ice.

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Antarctic sea-ice trends sustained by vertical ocean heat redistribution de Lavergne, Casimir1, Lecomte, Olivier2, Goosse, Hughes2, Fichefet, Thierry2, Barthélemy, Antoine2, Zunz, Violette3

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2Université Catholique de Louvain, Louvain-la-Neuve, Belgium 3Vrije Universiteit Brussel, Brussels, Belgium

Session 1.2 – February 6, 2018, 1000-1015

Since the beginning of the satellite observation era, the whole Antarctic sea-ice cover has slightly expanded. Several processes have been hypothesized to explain this apparent paradox in a global warming context, including externally forced changes in local winds or in the Southern Ocean’s hydrological cycle, as well as internal climate variability. Yet, the drivers behind recent Antarctic sea- ice trends are still debated, especially as current climate models fail to replicate them. Here, we show the critical influence of an ocean–sea-ice feedback mechanism. Once initiated by an external perturbation, it may be sufficient to sustain the observed sea-ice expansion in the Ross Sea, the region around Antarctica with the largest and most significant expansion. Using numerical experiments, hydrographic observations and sea-ice records, we quantify the heat trapped at the base of the ocean mixed layer and demonstrate that it is of the same order of magnitude as the latent heat storage due to the long-term changes in sea-ice volume. The evidence thus suggests that the recent increase in ice extent of the Ross Sea could have been achieved through a reorganization of energy within the near- surface ice-ocean system.

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22-year surface salinity changes in the seasonal ice zone near 140°e off Antarctica Morrow, Rosemary,1, Kestenare, Elodie1

Presenting author’s e-mail: [email protected]

1LEGOS-CNRS/CNES/IRD/University of Toulouse III, Toulouse, France

Session 1.2 – February 6, 2018, 1015-1030

Seasonal and interannual variations in surface salinity (SSS) are analysed in the Sea Ice Zone south of 60°S, from a 22-year time series of observations near 140°E. In the northern sea-ice zone during the warming cycle from October to March, waters warm by an average of 3.5°C and become fresher by 0.1 to 0.25. In the southern sea-ice zone, with cool surface temperatures of -1°C, the maximal SSS range occurs in December, with an average SSS of 33.65 near the Southern Boundary of the ACC, reaching 34.4 in the Modified Shelf waters close to the coast. The main fronts, normally defined at subsurface, are shown to have distinct seasonal characteristics in SSS and SST.

The interannual variations in SSS are more closely linked to variations in upstream sea-ice cover than surface forcing. SSS and sea-ice variations show distinct phases, with large biannual variations in the early 1990s, weaker variations in the 2000s and larger variations again from 2009 onwards. The calving of the Mertz Glacier Tongue leads to increased sea-ice cover and widespread freshening of the surface layers from 2011 onwards. Summer freshening in the northern sea-ice zone is ~ 0.05-0.07 decade-1, increasing to 0.08 decade-1 in the southern sea-ice zone, largely influenced by the Mertz Glacier calving event at the end of our time series. The summer time series of SSS on the shelf at 140°E is in phase but less variable than the SSS observed upstream in the Adélie Depression, and thus represents a spatially integrated index of the wider SSS variations.

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The role of convection in driving mixing in the Southern Ocean Sohail, Taimoor1, Gayen, Bishakhdatta1, Hogg, Andrew1,2

Presenting author’s e-mail: [email protected]

1Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia 2ARC Centre of Excellence for Climate System Science, Australian National University, Canberra, ACT 2601, Australia

Session 1.2 – February 6, 2018, 1100-1115

We use a direct numerical simulation to model a wind- and buoyancy-forced circumpolar ocean with the presence of turbulent convection. A suite of simulations is conducted at constant Rayleigh number, Ra ~ 1012 (where Ra is a nondimensional representation of buoyancy forcing) with varying wind stress magnitude. The Rayleigh number is larger than the critical Ra necessary to sustain turbulent convection in the buoyancy destabilising region. A circumpolar current is established by geostrophic balance, along with a large number of eddies. We estimate the mechanical energy budgets, energy sinks and mixing efficiency in the system, where mixing efficiency is defined as the strength of the diapycnal mixing relative to the total energy sink. The majority of dissipation occurs near the surface, underlying the region of high wind stress, whereas most diapycnal mixing exists within the boundary layer and inside the convective plumes. This study finds that the presence of convection drives higher diapycnal mixing relative to dissipation, resulting in high values of mixing efficiency. For circulation forced by wind and buoyancy in a domain comparable to the Southern Ocean, we estimate a high value of mixing efficiency, higher than previously thought.

23

An Indian Deep Water pathway along the south coast of Australia Tamsitt, Veronica1, Talley, Lynne1

Presenting author’s e-mail: [email protected]

1Scripps Institution of Oceanography, CA, USA

Session 1.2 – February 6, 2018, 1115-1130

Upwelling of deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of anthropogenic carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. Indian Deep Water (IDW) is an important source water mass of carbon and nutrient-rich deep water that feeds this upwelling. However, until recently the exact pathways that carry IDW from the Indian Ocean into the Antarctic Circumpolar Current (ACC) were not well characterized. New work has identified two dominant pathways of deep upwelling water exiting the Indian Ocean along its western and eastern boundaries. While a current has been identified in observations at 115°E by its eastward transport and low oxygen content, characteristic of IDW, the role of this flow as an important upwelling pathway has not been appreciated and its physical cause has not been shown. Here we characterize the eastern IDW pathway and investigate its underlying dynamics with a combination of hydrographic observations and Lagrangian experiments in an eddy-permitting model. We find an eastward flow extending between 1500 m and 4000 m along the Australian continental slope, reaching the Antarctic Circumpolar Current southwest of Australia. We hypothesize that an eddy thickness flux mechanism that has been shown to drive an eastern deep water pathway in the Atlantic may also operate in the Indian, driven by eddy transport around the southwest tip of Australia.

24

The impact of localised dense water overflows on ocean heat transport towards Antarctica Morrison, Adele1, Hogg, Andrew1, England, Matthew2, Spence, Paul2

Presenting author’s e-mail: [email protected]

1The Australian National University, ACT, Australia 2University of New South Wales, NSW, Australia

Session 1.2 – February 6, 2018, 1130-1145

Ocean transport across the Antarctic continental slope has a pivotal control on both the meridional overturning circulation, and global sea level. Circumpolar Deep Water upwells southward across the slope, transporting heat towards the floating Antarctic ice shelves. Dense Shelf Water cascades off the continental shelf, driving the abyssal overturning cell. In addition to the cross-slope transport of these globally significant mid-depth and bottom waters, Antarctic Surface Water also flows seasonally both on- and off-shore. Scarce observations and difficult modelling conditions mean that we know very little about what controls the cross-slope transport of these different water masses and if and how the transports are related to one another.

Using a high-resolution global ocean model, we have investigated the temporal and spatial variability of the ocean transport across the Antarctic continental slope. In the model, the formation of Dense Shelf Water on the shelf and its subsequent export is constrained to just three locations around Antarctica. Surprisingly, the majority of the on-shore transport of warm Circumpolar Dense Water is collocated with these localised overflow regions. We show how the modelled dense overflows modify the overlying stratification, creating conditions that allow for transport of warm mid-depth waters onto the continental shelf.

25

Geothermal heating enhancing upwelling in the Antarctic Circumpolar Current Downes, Stephanie1, Rintoul, Stephen2, Sloyan, Bernadette2, Lupton, John3

Presenting author’s e-mail: [email protected]

1Antarctic Climate and Ecosystems Cooperative Research Centre,TAS, Australia 2Commonwealth Scientific and Industrial Research Organization Oceans and Atmosphere, TAS Australia 3NOAA/Pacific Marine Environmental Laboratory, OR, USA

Session 1.2 – February 6, 2018, 1145-1200

The Antarctic Circumpolar Current (ACC) fronts are steered primarily by overlying westerly wind stress, surface buoyancy fluxes, and topography, with several hotspot regions of upwelling. However little attention has been paid to the role of geothermal heating, as a source of mixing along topographical features, in shaping the ACC fronts. Hydrothermal activity injects geothermal heat into the ocean at a rate of around 50mW m-2 in the abyssal plains and over 300mW m-2 along mid-ocean ridges. Hydrothermal signatures are found throughout the Southern Ocean, with the ACC overlying five major mid-ocean ridge segments. Numerous model-based studies have shown that this geothermal heating increases the global deep ocean circulation by around 25%, by destabilizing the ocean floor stratification with its constant buoyancy input. Here we use observations of helium, geothermal heat fluxes, physical water mass properties and inferred diffusivity estimates to show for the first time where hotspot upwelling regions in the ACC are associated with heightened geothermal heating. Heat that is injected into the ACC fronts on the equatorward side of coinciding mid-ocean ridges creates a strong localised vertical temperature gradient that increases upwelling rates for water masses greater than 28 kg m-3 (deep and bottom waters). Using coarse resolution model sensitivity experiments, we show that upwelling along hydrographic transects increases by more than 20% in regions where the ACC fronts coincide with strong geothermal heat fluxes. Our results hold particularly along the Pacific Antarctic Ridge, Southwest Indian Ridge and Scotia Ridge. This study highlights the need for Southern Ocean observational experiments to be designed with geophysical properties in mind, and emphasises the importance of include geothermal heating in climate models.

26

Deep bottom mixed layer instability drives intrinsic variability of the Antarctic Slope Front Huneke, Wilma1, Klocker, Andreas1,2, Galton-Fenzi, Ben2,3

Presenting author’s e-mail: [email protected]

1University of Tasmania, TAS, Australia 2ACE CRC, TAS, Australia 3Australian Antarctic Division, TAS, Australia

Session 1.2 – February 6, 2018, 1200-1215

Ocean-driven melting is an important factor for the mass loss of the Antarctic ice sheet. The ocean temperature on the continental shelf is subject to heat exchange across the Antarctic slope where the so-called Antarctic Slope Front (ASF) separates the cold continental shelf from the warmer Southern Ocean. Eddy-resolving regional models have recently improved our understanding of the mesoscale for cross-shelf heat exchange. Here we highlight the role of bottom mixed layer instabilities to weaken the ASF in areas of no active bottom water formation based on results from an idealised process- oriented model. Constantly produced eddy kinetic energy near the bottom leads every few years to a sudden outburst of vertical mixing that affects the entire water column. During these short periods, isopycnals flatten and lead to enhanced onshore heat flux. This mechanism is apparent in the model for both constant and seasonal forcing. The identified mechanism needs to be confirmed in models that are more realistic and the real ocean. Recent observations of the Antarctic margin’s lower slope indicate that such deep bottom mixed layers indeed exist and that they might be an important contributor to the Southern Ocean overturning circulation.

27

Intercomparison of Antarctic ocean/sea-ice/ice-shelf interactions simulated by two models Naughten, Kaitlin1,2,3, Meissner, Katrin1,2, Galton-Fenzi, Ben4,3, England, Matthew1,2, Timmermann, Ralph5, Hellmer, Hartmut5, Hattermann, Tore6,5, Debernard, Jens7

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, University of New South Wales, NSW, Australia 2ARC Centre of Excellence for Climate System Science, Australia 3Antarctic Climate and Ecosystems Cooperative Research Centre, TAS, Australia 4Australian Antarctic Division, TAS, Australia 5Alfred Wegener Institut, Germany 6Akvaplan-niva, Norway 7Norwegian Meteorological Institute, Norway

Session 1.2 – February 6, 2018, 1430-1445

Antarctic ice shelf cavities are set to become a standard component in ocean models, with an increasing number of models considering thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here we present a model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions as simulated by two models: MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and FESOM (Finite Element Sea-ice/Ice-shelf Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice shelf basal melting and sub-ice shelf circulation, as well as sea ice properties and Southern Ocean water mass characteristics as they influence the sub-ice shelf processes. Many key features of observations are reproduced by both models. However, significant areas of model disagreement remain, and both models struggle to reproduce the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen Seas. Several differences in model set-up show a particular influence on the simulations, such as topographic smoothing, vertical discretisation, and horizontal resolution.

28

Anatomy of a glacial meltwater discharge event in an Antarctic cove Meredith, Michael1, Falk, Ulrike2, Bers, Valeria2,3, Mackensen, Andreas2, Schloss, Irene4,5, Ruiz Barlett, Eduardo 4, Jerosch, Kerstin2, Silva Busso, Adrián6, Abele, Doris2

Presenting author’s e-mail: [email protected]

1British Antarctic Survey, Cambridge, United Kingdom 2Alfred Wegener Institute, Bremerhaven, Germany 3Now at: Leibniz-Centre for Tropical Marine Research, Bremen, Germany 4Instituto Antártico Argentino, Buenos Aires, Argentina 5CONICET, Argentina 6University of Buenos Aires, Argentina

Session 1.2 – February 6, 2018, 1445-1500

Glacial meltwater discharge from Antarctica is a key influence on the marine environment, impacting ocean circulation, sea level, and productivity of pelagic and benthic coastal ecosystems. The responses elicited depend strongly on the characteristics of the meltwater releases, including timing, spatial structure and geochemical composition. Here we use isotopic tracers to reveal the time-varying pattern of meltwater during a discharge event from the Fourcade Glacier into Potter Cove, northern Antarctic Peninsula. The discharge is strongly dependent on local air temperature, and the meltwater released interacts with ocean stratification and atmospherically-driven circulation to generate a strongly pulsed outflow from the cove to the ocean. Under low-turbulence conditions, the meltwater accumulates rapidly in an extremely thin, buoyant layer at the surface, with high turbidity reflecting a significant suspended particle load. These characteristics contrast with those further south along the Peninsula, where strong glacial retreat is driven oceanographically by intrusions of warm deep waters from offshore. The Fourcade Glacier switched recently to being land-terminating; if retreat rates elsewhere along the Peninsula remain high and glacier termini progress strongly landward, the structure and impact of the freshwater discharges are likely to increasingly resemble the patterns elucidated here.

29

On the importance of the circulation induced by ice-shelf melt for heat exchanges across the Antarctic continental shelf Jourdain, Nicolas1, Donat-Magnin, Marion1, Mathiot, Pierre2, Le Sommer, Julien,1, Durand, Gaël1, Spence, Paul3, Madec, Gurvan4

Presenting author’s e-mail: [email protected]

1IGE, CNRS/UGA/IRD/G-INP, Grenoble, France 2Met Office, Exeter, United Kingdom 3ARCCSS/CCRC, UNSW, Sydney, Australia 4LOCEAN, CNRS/IRD/UPMC/MNHN, Paris, France

Session 1.2 – February 6, 2018, 1500-1515

Circumpolar Deep Water (CDW) can get onto the Antarctic continental shelf in some regions like the Amundsen Sea and induce significant melting underneath ice shelves. Understanding the processes that control the CDW penetrations towards the ice shelves is extremely important because higher melt rates can trigger a marine ice-sheet instability with a resulting rapid contribution to sea level rise. The exchanges across the continental shelf are usually described through the contributions of eddies, tides, wind-driven circulation, and flow-topography interactions. In this presentation, we show that an additional crucial ingredient is the circulation induced by melting ice shelves. This work is based on a 1/12° configuration of the NEMO ocean model that includes ice-shelf cavities and which is deployed over the Amundsen Sea, Antarctica.

First, we run a series of experiments with varying heat exchange coefficients at the ocean/ice-shelf interface. This shows that the coastal current and inflow through topographic channels are strongly modulated by the melt intensity in ice-shelf cavities. The simulated melt-induced transport into the cavity is indeed 100 to 500 times stronger than the melt volume flux itself.

Then, we analyse the ocean response to shifting winds, and compare the results with and without melt in the ice-shelf cavities. Without ice-shelf melt, strengthening and poleward shifting winds tend to warm the deep waters on the continental shelf, as found in previous studies. By contrast, the presence of a melt-induced circulation is shown to cool deep waters. This stresses the need for including ice shelves in studies aiming to project coastal temperatures around Antarctica.

Finally, we use a model configuration representing the main tidal constituents, and we show how tides influence ice-shelf melt, which in turns creates a melt-induced residual circulation that feeds melt rates back.

30

Increased basal melting of the Mertz Glacier Tongue after calving Cougnon, Eva1,2, Galton-Fenzi, Ben3,4, Rintoul, Stephen2,4, Legrésy, Benoit2, Williams, Guy1,4, Fraser, Alex4, Hunter, John4

Presenting author’s e-mail: [email protected]

1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia 2Commonwealth Scientific and Industrial Research Organisation, Marine and Atmospheric Research, Hobart, Australia 3Australian Antarctic Division, Kingston, Australia 4Antarctic Climate & Ecosystems Cooperative Research Centre, Hobart, Australia

Session 1.2 – February 6, 2018, 1515-1530

Ice shelf basal melt is the dominant contribution to mass loss from Antarctic ice shelves. However, the sensitivity of basal melt to changes in icescape (grounded icebergs, ice shelves and fast ice) and related ocean circulation is poorly understood. Here, we simulate the impact of the major East Antarctic calving event of the Mertz Glacier Tongue (MGT) in 2010, and related redistribution of sea ice and icebergs on the basal melt rate of the local ice shelves. We find that a large tabular iceberg (B9B) near the main ice shelves controls the water masses that reach the ice shelf cavities. After the calving and the removal of B9B, warmer water is present both within the MGT cavity and on the continental shelf driving an 89% increase in the area-averaged basal melting of the MGT. Changes in icescape control the oceanic heat flux responsible for basal ice shelf melting. In order to understand any individual ice shelf, it is therefore important to consider the wider regional setting and icescape, including surrounding ice shelves and large grounded tabular icebergs.

31

Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water Silvano, Alessandro1,2, Rintoul, Stephen2,3,4, Peña-Molino, Beatriz3, Hobbs, William R.3,5, van Wijk, Esmee2, Aoki, Shiger6, Tamura, Takeshi3,7,8, Williams, Guy D.1,3,5

Presenting author’s e-mail: [email protected]

1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia 2CSIRO Oceans & Atmosphere, Hobart, TAS, Australia. 3Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, TAS, Australia. 4Centre for Southern Hemisphere Oceans Research, Hobart, TAS, Australia 5Antarctic Research Council Centre of Excellence for Climate System Science, University of New South Wales, Sydney, NSW, Australia, 2052 6Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan 7National Institute of Polar Research, Tachikawa, Japan 8SOKENDAI, Graduate University for Advanced Studies, Tachikawa, Japan

Session 1.2 – February 6, 2018, 1530-1545

Strong heat loss and brine release during sea-ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea-ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm waters from the Southern Ocean can spread across the continental shelf at depth and reach the ice-shelf cavities to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial-meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea-level rise.

32

Hotspot of carbon fluxes along the Polar Front Langlais, Clothilde1, Hauck, Judith2, Sallée, Jean-Baptiste3, Klocker, Andreas4, Conde Pardo, Paula5, Rintoul, Stephen1,5, Lenton, Andrew1,5

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Climate Science Centre, Hobart, TAS, Australia 2AWI, Bremerhaven, Germany 3LOCEAN-IPSL, Sorbonnes Université (UPMC), Paris, France 4IMAS, University of Tasmania, Hobart, TAS, Australia 5Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, TAS, Australia

Session 1.2 – February 6, 2018, 1645-1700

The Southern Ocean is an important contributor to carbon cycling and is of most importance for our global climate. The capacity of the ocean to store and sequester carbon is set by the ocean circulation which transfers carbon in and out of the deep ocean. Old carbon- and nutrient-rich deep water is brought to the surface via large-scale upwelling south of the Polar Front driven by the Westerly winds. In pre-industrial times, this process used to release CO2, so-called natural carbon. However, the rise of atmospheric CO2 ever since suppresses this outgassing more and more transforming the upwelling regions into new sinks of anthropogenic carbon. Here, we use biogeochemical eddy-resolving ocean simulations (1/10°) that allow us to assess the role of ocean dynamics and eddy processes in controlling carbon fluxes. South of the Polar Front, hot spots of natural carbon outgassing and anthropogenic carbon uptake occur near topographic obstacles. We discuss potential physical– biological mechanisms through which fronts merging and baroclinic instabilities may affect carbon fluxes and pathways. By gaining in-depth process understanding of the physical and biological drivers of the Southern Ocean sink, we can better understand the present-day carbon fluxes and trend, and deliver improved projections of the SO carbon sink for the 21st century.

33

Eddies lengthen streamlines at standing meanders as observed by Argo floats Katsumata, Katsuro1

Presenting author’s e-mail: [email protected]

1RCGC, JAMSTEC, Japan

Session 1.2 – February 6, 2018, 1700-1715

Argo floats measure horizontal current velocities at the parking depth and vertical profiles of temperature and salinity. These data were used to study the roles that eddies play near standing meanders of the Antarctic Circumpolar Current (ACC). These standing meanders have been explained as nondivergent barotropic Rossby waves trapped by the eastward flow of the ACC. Recent numerical simulations found a link between the length of buoyancy contours (or “streamlines”) and barotropic adjustment of the ACC to increased wind forcing – an increase in amplitude and/or wavelength of the trapped Rossby waves. Climatological hydrographic data and the eddy field estimated by the Argo floats are interpreted as steady and perturbation fields, respectively. Average curvature of streamlines of transport in the upper 1000 dbar around seven major standing meanders along ACC shows that eddies lengthen the streamlines around the standing meanders. In particular, poleward eddy transport on the eastern flanks of meridional ridges is found important in this adjustment process.

34

New perspectives on Southern Ocean jets, fronts and their variability Chapman, Christopher1, Sallée, Jean-Baptiste1, Capet, Xavier1

Presenting author’s e-mail: [email protected]

1LOCEAN-IPSL, Sorbonne Universities, Paris, France

Session 1.2 – February 6, 2018, 1715-1730

The frontal structure of the Southern Ocean is investigated using a sophisticated frontal detection method. This methodology is applied to 21 years of satellite sea-surface height altimetry, and to the output of an idealised, eddy-resolving model with simple topography. By forming frontal occurrence frequency maps and then approximating these occurrence maps by a Gaussian Mixture Model (GMM), the time-mean locations of the fronts, as well as a measure of their capacity to meander, are obtained and related to the frontal locations found by previous studies.

The spatial and temporal variability of the frontal structure is then considered. Using the altimetric data, we show that the number of fronts is found to be highly variable throughout the Southern Ocean, increasing (splitting) downstream of large bathymetric features and decreasing (merging) in regions where the fronts are tightly controlled by the underlying topography.

These splitting/merging events are related to changes in the underlying frontal structure whereby regions of high frontal occurrence cross or spread over streamfunction contours. In contrast to the number of fronts, frontal meandering remains relatively constant throughout the Southern Ocean. Little to no migration of the fronts over the 1993–2014 time period is found, and there is only weak sensitivity of frontal positions to atmospheric forcing related to the southern annular mode or the El Niño–Southern Oscillation.

Finally The physics of the frontal variability is elucidated in the numerical model using a novel framework based on Q-vectors used to diagnose frontogenesis in the atmosphere.

35

Fingerprints of eddy stirring suppression in Antarctic Circumpolar Current jets Phillips, Helen1,2, Naveira Garabato3, Alberto, Polzin4, Bindoff, Nathan1,2,5,6, Waterman, Stephanie7

Presenting author’s e-mail: [email protected]

1IMAS, University of Tasmania, Australia 2ARC Centre of Excellence in Climate Systems Science, Australia 3National Oceanography Centre, UK 4Woods Hole Oceanographic Institution, USA 5Antarctic Climate and Ecosystems CRC, Australia 6CSIRO Oceans and Atmosphere, Australia 7University of British Columbia, Canada

Session 1.2 – February 6, 2018, 1730-1745

We present a unique highly-resolved, along-stream view of temperature, salinity and velocity within the upper 1600 meters of the ACC where the mean flow is strong. These semi-Lagrangian EM-APEX profiling float observations provide a sharp contrast to the way we traditionally observe the Southern Ocean, where cross-frontal transects and strong meridional gradients dominate the picture. Rather, what we find are thermohaline filaments that trail along the ACC for many hundreds of kilometres. This coherence is inconsistent with the traditional view of thermohaline variability in the ocean. Moreover, we find a striking behaviour of the thermohaline anomalies in crossing isopycnals to converge near the bottom of the thermocline.

Our interpretation is that the EM-APEX are tracking anomalies that originate with relatively large vertical scales, and these vertical scales are diminished as the thermal wind shear of the ACC differentially advects the anomalies to tilt them in the vertical. We present a simple kinematic model that assumes production of thermohaline variance by barotropic motions at large horizontal scales, a suppression of eddy stirring by smaller horizontal scale motions and a spatially uniform thermal wind shear that mimics the behavior seen by the floats. We also examine the trajectories of particles seeded into the time-varying SatGEM climatology at the time and location of our observations. We find the production of filaments at crests and troughs of ACC meanders that are sheared and stretched to form coherent ribbons of fluid many 100s of km long. The coherence of the anomalies in the observations, kinematic model and particle tracking results argues for eddy suppression in the ACC and a long dissipation time scale.

36

1.3 Ocean extreme events and their impacts Prediction of extreme ocean conditions in Australia Brassington, Gary1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, NSW, Australia

Session 1.3 – February 8, 2018, 1100-1115

A range of extreme ocean conditions in Australia’s regional seas and coastal shelf since the 1990s are presented based on mesoscale and coastal resolving systems. In this context, we identify extremes statistics of state variables from a multi-year reanalyses which by definition lie in the tail of the distribution and are both extreme in magnitude and rare. Given the design of the modelling system and the observing system extreme conditions will focus on the upper ocean and continental shelf. A number of key properties are examined: (a) causation and leading indicators and (b) how the extreme condition evolves in time and covary in space and with other state variables. A selection of contemporary events will be further examined in terms of their detection in the deterministic forecasts. Given their low probability a single forecast of an extreme condition requires an extensive procedure to develop sufficient confidence that would warrant acting on the information. Multi-cycle ensemble, consensus forecasts and ensemble forecasts will be examined for their guidance of these contemporary events.

37

Multi-year persistence of the 2014/15 North Pacific marine heatwave Di Lorenzo, Emanuele1, Mantua, Nathan2

Presenting author’s e-mail: [email protected]

1Georgia Institute of Technology, GA, USA 2National Marine Fisheries Service, National Oceanographic and Atmospheric Administration, CA, USA

Session 1.3 – February 8, 2018, 1115-1130

Between the winters of 2013/14 and 2014/15 during the strong North American drought, the northeast Pacific experienced the largest marine heatwave ever recorded. Here we combine observations with an ensemble of climate model simulations to show that teleconnections between the North Pacific and the weak 2014/2015 El Niño linked the atmospheric forcing patterns of this event. These teleconnection dynamics from the extratropics to the tropics during winter 2013/14, and then back to the extratropics during winter 2014/15, are a key source of multi-year persistence of the North Pacific atmosphere. The corresponding ocean anomalies map onto known patterns of North Pacific decadal variability, specifically the North Pacific Gyre Oscillation (NPGO) in 2014 and the Pacific Decadal Oscillation (PDO) in 2015. A large ensemble of climate model simulations predicts that the winter variance of the NPGO- and PDO-like patterns increases under greenhouse forcing, consistent with other studies suggesting an increase in the atmospheric extremes that lead to drought over North America.

38

Coral bleaching pathways under the control of regional temperature variability Langlais, Clothilde1, Lenton, Andrew1, Heron, Scott F.2, Evenhuis, Chris1,3, Sen Gupta, Alex4, Brown, Jaclyn N.5, Kuchinke, Mareva1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Climate Science Centre, Hobart, TAS, Australia 2NOAA Coral Reef Watch, Townsville, QLD, Australia 3University of Technology Sydney, NSW, Australia 4Climate Change Research Centre and ARC Center of Excellence for Climate System Science University of New South Wales, NSW, Australia 5CSIRO Agriculture and Food, Hobart, TAS, Australia

Session 1.3 – February 8, 2018, 1130-1145

Increasing sea surface temperatures (SSTs) are predicted to adversely impact coral populations worldwide through increasing thermal bleaching events. Future bleaching is unlikely to be spatially uniform. Therefore understanding what determines regional differences will be critical for adaption management. Here, using a cumulative heat stress metric, we show that characteristics of regional SST determine the future bleaching risk patterns. Incorporating observed information on SST variability, in assessing future bleaching risk, provides novel options for management strategies. As a consequence, the known biases in climate model variability and the uncertainties in regional warming rate across climate models are less detrimental than previously thought. We also show that the thresholds used to indicate reef viability can strongly influence a decision on what constitutes a potential refugia. Observing and understanding the drivers of regional variability, and the viability limits of coral reefs, is therefore critical for making meaningful projections of coral bleaching risk.

39

Australian Wave Setup Hindcast O’Grady, Julian1, McInnes, Kathleen1, Hoeke, Ron1, Hemer, Mark2

Presenting author’s e-mail: [email protected]

1CSIRO, VIC, Australia 2CSIRO, TAS, Australia

Session 1.3 – February 8, 2018, 1145-1200

Severe storm events can cause elevated sea levels through storm surge (i.e. inverse barometer effect and wind setup) as well as the breaking of wind-waves at the coast, which produce an additional time- averaged contribution to extreme sea levels through wave setup. The storm surge component of extreme sea levels is represented numerically by running hydrodynamic models. However, the representation of wave setup requires running near-shore wave models at high spatial resolution to either simulate the wave setup directly using internal parameterisations or provide wave stress forcing terms for incorporation into hydrodynamic models. Either option adds computational complexity to the problem and is often not feasible. An alternative approach described in the present study is the development of a semi-empirical wave setup equation, which has been developed on the basis of numerical model simulations using the SWAN nearshore wave model for the Australian coastline. This model provides a simple prediction of wave setup for incident wave conditions, (significant wave height, peak wave period, and bathymetric slope). The equation is applied to a ~32-year hindcast of ocean waves (CAWCR-WW3) at ~7000 coastal points around Australia. Extreme value analysis applied to the wave-setup hindcast will present insight into additional impact of waves on coastal extremes (e.g. storm surge and tide) and the potential coastal exposure arising from large wave events.

40

Marine heatwaves in the South Atlantic Rodrigues, Regina1, Taschetto, Andréa2

Presenting author’s e-mail: [email protected]

1Federal University of Santa Catarina, Santa Catarina, Brazil 2Climate Change Research Centre, University of New South Wales, NSW, Australia

Session 1.3 – February 8, 2018, 1200-1215

In this study, we investigate the occurrence of marine heatwave events in the western South Atlantic during austral summer for the period of 1979-2016. We find that marine heatwaves are mainly associated with atmospheric blocking events that prevent the establishment of South Atlantic Convergence Zone (SACZ) during austral summer. The decrease in cloud cover associated with the absence of the SACZ enhances the heat flux into the ocean causing the extreme sea surface temperature (SST) episodes. Satellite-derived SST anomalies in January and February 2014 peaked at 3°C above the long-term monthly means over a wide area from the South American coast to the middle of the South Atlantic basin (25-35°S, 0-50°W). This particular marine heatwave event was associated with an atmospheric blocking episode that lasted for more than 30 days and also caused the worst drought ever recorded over the southeast Brazil. Marine heatwave events impact the primary productivity in this region. As expected, there is a decrease in primary productivity over the western South Atlantic deep ocean where the SST anomalies are highly positive. However, along the Brazilian continental shelf, the wind anomalies associated with atmospheric blocking enhance coastal upwelling that combined with more available shortwave radiation increases primary productivity locally.

41

1.4 Collaborative Research under the Centre for Southern Hemisphere Ocean Research (CSHOR) Centre for Southern Hemisphere Oceans Research (CSHOR) Cai, Wenju1,2

Presenting author’s e-mail: [email protected]

1Centre for Southern Hemisphere Oceans Research (CSHOR), CSIRO Oceans and Atmosphere, Hobart, Australia 2Physical Oceanography Laboratory/CIMST, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Yushan Road, Qingdao, China

Session 1.4 – February 5, 2018, 1100-1115

CSHOR is an international collaboration between Qingdao National Laboratory for Marine Science and Technology (QNLM), CSIRO, UNSW and UTAS, focusing on Indo-Pacific tropical variability, inter-basin exchange, warm pool dynamics, Southern Ocean processes, sea level, and Antarctic observations. The establishment attests to Australia’s world-leading capability, which underpins this collaboration, its value and its contribution to our understanding of the role of Southern Hemisphere Oceans to regional and global climate. In this presentation, I will introduce CSHOR’s research activities and report the latest achievements, including the risks of tropical Indo-Pacific climate extremes associated with the Paris Agreement, potential impact of model biases on climate projection, and forcing of recent accelerated sea level rise. I will also discuss further collaboration opportunities arising from this collaboration.

42

Unusually warm Indian Ocean sea surface temperatures arrest development of El Niño in 2014 McPhaden, Michael1, Dong, Lu2

Presenting author’s e-mail: [email protected]

1NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington, USA

Session 1.4 – February 5, 2018, 1115-1130

In early 2014, strong westerly wind bursts and high heat content in the equatorial Pacific favored development of a major El Niño event. However, significant coupling between the Pacific Ocean and atmosphere failed to take hold during boreal summer of 2014 such that only borderline El Niño conditions were evident by the end of the year. In this study, we hypothesize that warm Indian Ocean sea surface temperatures (SSTs) in 2014 helped to arrest the development of El Niño by altering the tropical circulation so as weaken westerly wind anomalies in the western Pacific. We test this hypothesis using an ensemble of coupled numerical experiments in which observed Indian Ocean SST anomalies in 2014–15 are prescribed but the Pacific ocean-atmosphere system is free to evolve. Our results confirm that warm SST anomalies in the Indian Ocean created conditions that would have favoured a weakening of El Niño in 2014.

43

The acceleration and 60 year oscillation in global sea levels Church, John A.1, Abellán, Esteban1, Spada, Giorgio2, Olivieri, Marco3, Meyssignac, Benoit4, Slangen, Aimée5, Richter, Kristen6

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, University of New South Wales, NSW, Australia. 2DISPEA, University of Urbino, Italy. 3INGV, Bologna, Italy 4LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France. 5Royal Netherlands Institute for Sea Research, Department of Estuarine & Delta Systems. 6University of Innsbruck, Austria.

Session 1.4 – February 5, 2018, 1130-1145

An acceleration and 60 year oscillation has been reported in estimates of global mean sea level, and in tide-gauge observations of regional sea level for the 20th century. We analyse model estimates of 20th century sea-level change. These model estimates are based on CMIP5 models for ocean thermal expansion and changes in surface temperature and precipitation affecting cryospheric changes, as well as changes in land-water storage. The ensemble mean averages out much of the internal natural variability in sea level and has significant skill in reproducing observed regional sea-level change. Using the average of the CMIP5 ensemble, we find a coherent large-scale 60 year cycle in regional and global mean sea level that is directly related to natural forcing changes, with additional but smaller signals from corrections to the cryospheric contributions and from the land-water storage. The acceleration is mostly related to anthropogenic forcing. We compare these model results with observational estimates of the low frequency variability.

44

The CSHOR Southern Ocean Dynamics Project England, Matthew H.1, Rintoul, Stephen R.2

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre (CCRC) and ARC Centre of Excellence for Climate System Science, University of New South Wales, NSW, Australia 2CSIRO Oceans and Atmosphere, TAS, Australia

Session 1.4 – February 5, 2018, 1145-1200

The Southern Ocean has recently undergone significant changes in ocean thermal structure, with recent observations indicating rapid surface warming in the Amundsen-Bellingshausen Seas (Jones et al. 2016), over the shelf around parts of the Antarctic margin (Schmidtko et al. 2014) and in the abyssal bottom water layers (Purkey and Johnson, 2010, 2012, 2013). Yet our understanding of the underlying mechanisms driving these three different warming patterns remains fragmented and incomplete. The CSHOR Southern Ocean Dynamics Project aims, among other activities, to further our understanding of the processes by which oceanic temperatures are changing around Antarctica, particularly the above patterns of warming, by exploiting cutting edge ocean-sea ice models guided by (and evaluated against) the most recent ocean observations, alongside theory. Other objectives of the research program include improved understanding of the Southern Ocean carbon cycle, better knowledge of ocean-ice interactions and feedbacks around the Antarctic margin, and an improved understanding of the mechanisms controlling future changes in the Antarctic Circumpolar Current and its eddy field. This talk will overview the proposed activities of the CSHOR Southern Ocean Dynamics Project, with a particular focus on uncovering the mechanisms of Southern Ocean warming that have played out over the past half century, and how these might evolve into the future.

45

Response of tropical Pacific climate variability to multi-decadal high latitude forcing Santoso, Agus1,2

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2CSIRO, TAS, Australia

Session 1.4 – February 5, 2018, 1200-1215

The tropical Pacific is home to prominent modes of climate variability, the El Nino Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO), which exert significant impact on global and regional climates. For many decades the scientific community has been intrigued by the complexity of ENSO behaviour such as its decadal variations and how it relates to decadal modes of variability that are intrinsic to the tropical Pacific (e.g., IPO) or remote regions (e.g., Atlantic Multidecadal Oscillation). For instance, is ENSO influenced by phases of the IPO, or is it more that the IPO itself is a consequence of ENSO variations? Addressing such an issue is difficult given the close interactions across modes. However, some useful insights can be gained into the nature of tropical Pacific variability using idealised experiments. In this study, a coupled climate model is used to perform two sets of experiments. In the first set, a periodic freshwater signal is applied around Antarctica with different intensities and multi-decadal periodicities. In the other, the forcing is applied in the North Atlantic with identical intensities and periodicities as the first set. The forcing locations have been chosen for their paleo significance and each experiment is run for at least 500 years. The results show that ENSO responds differently to these contrasting sources of multi-decadal signal, albeit the identical forcing amplitudes and periods. This stems from the different transmission pathways of multi-decadal signal into the tropical Pacific between the two sources: the more prominent oceanic pathway for the Southern Ocean source, and the atmospheric pathway for the North Atlantic source. This study also has paleo implications wherein significant changes occur not just in the tropical Pacific but also in high-latitude regions.

46

Using past changes to improve models of the Antarctic Ice Sheet Phipps, Steven J.1, King, Matt A.1, Roberts, Jason L.2,3, White, Duanne A.4

Presenting author’s e-mail: [email protected]

1University of Tasmania, Tasmania, Australia 2Australian Antarctic Division, Tasmania, Australia 3Antarctic Climate & Ecosystems Cooperative Research Centre, Tasmania, Australia 4University of Canberra, ACT, Australia

Session 1.4 – February 5, 2018, 1215-1230

Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthermore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modelling is therefore a poorly constrained exercise. The past evolution of the AIS provides an opportunity to improve the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level.

We use the Parallel Ice Sheet Model (PISM) to demonstrate how past changes can be used to improve our ability to predict the future evolution of the AIS. A large perturbed-physics ensemble is generated, spanning uncertainty in the parameterisations of key physical processes within the model. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum (~21,000 years ago) until 5,000 years into the future. Records of past ice sheet thickness and extent are then used to determine which ensemble members are the most realistic. This allows us to use the known history of the AIS to constrain our understanding of its past contribution towards changes in global sea level. Critically, it also allows us to determine which ensemble members are most likely to generate realistic projections of the future evolution of the AIS. This enables us to use past changes in the AIS to reduce uncertainty in projections of future sea level rise.

47

The increasing rate of global mean sea-level rise during 1993-2014 Chen, Xianyao1, Zhang, Xuebin2, Church, John A.3, Watson, Christopher S.4, King, Matt A.4, Monselesan, Didier2, Legrésy, Benoit2, Harig, Christopher5

Presenting author’s e-mail: [email protected]

1Physical Oceanography Laboratory/CIMST, Ocean University of China, and Qingdao National Laboratory of Marine Science and Technology, Shandong, China 2CSIRO Oceans and Atmosphere, TAS, Australia 3Climate Change Research Centre, University of New South Wales, NSW, Australia 4Discipline of Geography and Spatial Sciences, School of Land and Food, University of Tasmania, TAS, Australia 5Department of Geosciences, University of Arizona, AZ, USA

Session 1.4 – February 5, 2018, 1445-1500

Global mean sea level (GMSL) has been rising at a faster rate during the satellite altimetry period (1993–2014) than previous decades, and is expected to accelerate further over the coming century. However, the accelerations observed over century and longer periods have not been clearly detected in altimeter data spanning the past two decades. Here we show that the rise, from the sum of all observed contributions to GMSL, increases from 2.2 ± 0.3 mmyr-1 in 1993 to 3.3 ± 0.3 mmyr-1 in 2014. This is in approximate agreement with observed increase in GMSL rise, 2.4 ± 0.2 mmyr-1 (1993) to 2.9 ± 0.3 mmyr-1 (2014), from satellite observations that have been adjusted for small systematic drift, particularly affecting the first decade of satellite observations. The mass contributions to GMSL increase from about 50% in 1993 to 70% in 2014 with the largest, and statistically significant, increase coming from the contribution from the Greenland ice sheet, which is less than 5% of the GMSL rate during 1993 but more than 25% during 2014. The suggested acceleration and improved closure of the sea-level budget highlights the importance and urgency of mitigating climate change and formulating coastal adaption plans to mitigate the impacts of ongoing sea-level rise (doi:10.1038/NCLIMATE3325).

48

Coupled atmosphere-ocean dynamics in the eastern Indian Ocean warm pool Feng, Ming1,2, Wijffels, Susan2, Hendon, Harry3

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Indian Ocean Marine Research Centre, Crawley, Australia. 2Centre for Southern Hemisphere Oceans Research, Hobart, Australia. 3Bureau of Meteorology, Melbourne, Australia

Session 1.4 – February 5, 2018, 1500-1515

High frequency coupling between the tropical upper ocean and atmosphere at diurnal time scales is being recognized as important for the behaviour of largescale climate modes such as the Madden Julian Oscillation (MJO). The MJO is a key source of predictability for medium term weather in Australia and Asia, and may also play a role in the initiation and termination of El Nino Southern Oscillation events. MJO is also important in the evolution of marine heatwave events off northern Australia and drives significant boundary current variability. High temporally resolved observations which capture this co-variability are scarce, restricted to a few sites and short intensive field campaigns. None have been obtained in the highly active MJO and diurnal cycle region off Australia’s North West Shelf. Medium-term weather and seasonal climate forecasting and modelling systems, in turn, require high vertical resolution in the upper ocean and fast coupling rates to capture the non-linear nature of this interaction, presenting a computational challenge for forecasting systems.

Under the CSHOR warm pool dynamics project, we plan to carry out a field study off northwest Australia with a novel combination of robotic platforms to capture the fast ocean/atmosphere coupling on diurnal timescales without the need to access research vessel time or resort to a fully equipped moored flux site. The study will capture the upper ocean and surface atmosphere variability off the very active MJO/diurnal cycle hot spot off the northwest coast of Australia, to guide sensitively experiments in the coupled system to quantify the impact of the fast coupling or upper ocean mixing rates on the simulated diurnal cycle, MJO and seasonal climatology.

49

An episodic change in the SST-precipitation relationship during boreal spring in the western tropical Pacific and its associated atmospheric teleconnections Hyun-Su, Jo1, Sang-Wook, Yeh2, Wenju, Cai1

Presenting author’s e-mail: [email protected]

1CSIRO Ocean and Atmosphere, Aspendale, Victoria, Australia 2Department of Marine Sciences and Convergent Technology, Hanyang University, ERICA, Ansan, Republic of Korea

Session 1.4 – February 5, 2018, 1515-1530

A relationship exists between sea surface temperature (SST) and precipitation in the western tropical Pacific (WTP) during boreal spring (March-April-May, MAM), in which higher SSTs are associated with higher precipitation. We found that this positive SST-precipitation relationship became episodically weak from the late 1990s to the early 2010s (1999-2014). We examine the physical processes associated with the weakening and its associated atmospheric teleconnections from the WTP to the mid-latitudes. Using data for the period of 1980-2016 excluding data for 1999-2014, anomalous warm SSTs induce higher precipitation through low-level convergence associated with a cyclonic circulation in the WTP. Subsequently, enhanced convection acts to dampen anomalous warm SSTs by reflecting incoming solar radiation but oceanic processes related to a deepening thermocline more than offset a negative tendency of SST. These processes operate in an opposite direction for a cool SST anomaly. This results in a significant positive SST-precipitation relationship. During 1999-2014, damping by surface heat fluxes dominates the oceanic processes, resulting in a weakening of the SST-precipitation relationship. This study suggests that the change might be related to the mean state change for 1999- 2014. Furthermore, the change in the SST-precipitation relationship leads to a changing sensitivity of precipitation and atmospheric heating structure to the anomalous SST in the WTP, which modifies atmospheric teleconnections in the mid-latitudes, including a different response of surface temperature and precipitation in the US to the anomalous SST in the WTP.

50

1.5 South Atlantic Ocean: circulation, processes, observations and modelling Climate drivers of the South Atlantic Subtropical Mode Water Sato, Olga1, Polito, Paulo1, Bernardo, Piero1, Taschetto, Andréa2

Presenting author’s e-mail: [email protected]

1University of São Paulo, SP, Brazil 2University of New South Wales, NSW, Australia

Session 1.5 – February 8, 2018, 0930-0945

Mode waters are distinct layers in the upper ocean that have remarkably low stratification. They form from winter to mid-spring, a period marked by harsh weather due to strong winds associated with low air temperature and low relative humidity. During that time, the subsurface layers outcrop and expose previously formed mode water to the surface. The seasonal thermocline that forms during the spring and summer isolates that new layer between the seasonal and the permanent thermoclines. The South Atlantic subtropical mode waters (SASTMW) occupy three distinct regions: i) the Brazil Current recirculation gyre on the western side, ii) near the Agulhas retroflection in eastern side, and iii) along the southern edge of the gyre. We investigate how the changes in the SASTMW volume are correlated to inter-annual scale variability such as ENSO, PDO, DMI among others. For this analysis, we used a 3D monthly mean field of global temperature and salinity based on in situ data, In Situ Analysis System (ISAS) from IFREMER, and model outputs from the Community Earth System Model (CESM) and the Australian Community Climate and Earth-System Simulator (ACCESS). ISAS- derived volume showed a significant correlation of -0.6 (at 95% confidence level) with the NINO3.4 index. The mechanisms of how it influences the presence of mode water are being investigated. For instance, during positive ENSO phases, changes in the precipitation and cloud cover patterns could lead to changes in the latent heat flux and thus to a decrease in the formation of SASTMW. In the eastern side, correlations with the Antarctic Oscillation (AAO) reach -0.4 that could be related to changes in the wind stress field and upwelling through Ekman dynamics leading to more dissipation of mode waters. Model-based results show smaller but still significant correlations that agree with the sign of the correlations.

51

A budget analysis of the SAMOC at 22°S and 34.5°S using observational based reconstruction Goes, Marlos1,2, Majumder, Sudip1,2, Schmid, Claudia2, Dong, Shenfu2

Presenting author’s e-mail: [email protected]

1University of Miami/CIMAS, FL, USA 2NOAA/AOML, FL, USA

Session 1.5 – February 8, 2018, 0945-1000

Time series of Meridional Overturning Circulation (MOC), Meridional Heat Transport (MHT) and Fresh water transport (MOV) are constructed using a blended product that involves observations from Argo floats, XBT, satellite Altimetry, and reanalysis wind fields in the years 1993 to 2015 at 22°S and 34.5°S in the South Atlantic. This blended product and numerical model simulations are used to analyse the variability of MOC, MHT and MOV from seasonal to interannual time scales. We quantify how the inclusion of high density XBT observations near the coast in the blended product improves the representation of the variability of the Brazil Current and the estimates of MOC, MHT and MOV at these latitudes. In addition to this, we disentangle the contribution of salinity and velocity changes to the advection of freshwater across these latitudes, as well as a freshwater budget of heat and freshwater budget is performed between these two latitudinal sections to understand the importance of the circulation components to the total variability of these quantities. The first timeseries is derived using observed salinity and velocity, and the second uses observed velocity and annual values of the observed salinity.

52

Impact of mesoscale dynamics in the South Atlantic and the Agulhas region on the South Atlantic Meridional Overturning Circulation Schwarzkopf, Franziska U.1, Biastoch, Arne1, Jan, Harlaß1

Presenting author’s e-mail: [email protected]

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany

Session 1.5 – February 8, 2018, 1000-1015

The Agulhas Current (AC) has been shown to play an important role not only in the connectivity between the Indian and Atlantic oceans but also for the south-to-north interhemispheric exchange in the Atlantic. The greater AC system is highly dominated by mesoscale processes. To investigate their influence onto the regional and global circulations, a family of high-resolution ocean general circulation model configurations based on the current NEMO code has been developed. The INALT family utilizes high-resolution "nests" covering the South Atlantic and the western Indian Ocean at 1/10°, 1/20° and (for the Agulhas region) up to 1/60° resolution in global models at coarser resolution. Nests and hosts are connected through two-way interaction, allowing the nests not only to receive boundary conditions from their respective host, but also to transmit the mesoscale impact into the global ocean.

We will show that large-scale, integral measures turn out to be rather robust amongst the simulations, whereas a proper representation of the AC dynamics depends on the mesoscale resolution. By varying resolutions and nested domains, we will disentangle the individual effects of a resolved mesoscale in the Atlantic sector of the Antarctic Circumpolar Current and in the AC system on the South Atlantic Meridional Overturning Circulation.

53

1.6 Oceanic pathways from the Subtropical Southwest Pacific Sea Surface Temperature Trends and Variability in the Southwest Pacific Bowen, Melissa1, Shears, Nick1, Sutton, Phil1,2, Markham, J.1, Zhang, Xuebin3, Fernandez, Denise2, Wu, Quran3

Presenting author’s e-mail: [email protected]

1University of Auckland, Auckland, New Zealand 2NIWA, Wellington, New Zealand 3CSIRO, Hobart, Australia

Session 1.6 – February 8, 2018, 1645-1700

We investigate temperature trends and variability in the Southwest Pacific from coastal temperature records, satellite sea surface temperatures and an ocean state estimate. From the three coastal records spanning half a century, the greatest rate of warming is off eastern Tasmania (0.20oC/decade), followed by southern New Zealand (0.10oC/decade), while there was no evidence of warming in northeastern New Zealand. These regional variations are also evident in the shorter satellite record and are consistent with the expected response of flow in the western boundary currents to increasing South Pacific wind stress curl. We further investigate mechanisms causing temperature variability from the heat balance in an ocean state estimate. We find that changes in upper ocean temperature around New Zealand are caused by the convergence and divergence of heat transport due to ocean dynamics as well as air-sea heat exchange. Therefore, in addition to advection by the boundary currents, we suggest the depth of the thermocline adjusts to changes in South Pacific winds modifying the vertical advection of heat into the upper ocean and contributing to variability of sea surface temperatures in the region.

54

Projected changes in southwest Pacific Ocean circulation and temperature extremes in a future climate Holbrook, Neil1,2, Oliver, Eric1,2, Wotherspoon, Simon1, Chamberlain, Matthew3, O’Kane, Terence3

Presenting author’s e-mail: [email protected]

1University of Tasmania, TAS, Australia 2ARC Centre of Excellence for Climate System Science, TAS, Australia 3CSIRO Oceans and Atmosphere, TAS, Australia

Session 1.6 – February 8, 2018, 1700-1715

The surface waters of the western Tasman Sea are warming at almost four times the global average rate, and modelling studies suggest that the increased sea surface temperature (SST) is largely due to a ‘spin-up’ of the South Pacific Gyre (SPG) over recent decades. However, given the complex nature of the western boundary current system in the Pacific, the consequences of the spin-up of the SPG in this region are not obvious. The enhanced transport does not represent a simple change in the mean flow, but rather complex pulse and eddy changes that also contribute to extreme SST events, and which can result in substantial ecological impacts off southeast Australia.

Here we discuss 21st Century changes in the southwest Pacific circulation and temperature extremes based on output from dynamically downscaled (eddy-resolving) climate change projections for the region. We present the projected Tasman Sea marine climate in terms of changes in mean SST and SST variance, the occurrence of extreme SST events, and mean circulation and eddy characteristics. We find that the mean SST is projected to increase in a hotspot located in the Tasman Sea, while the maximum variance is not co-located with the mean but rather pushed further southwards and towards the coast. We will discuss contributions to the temperature changes both from the mean circulation using an Island Rule calculation and through changes in the eddy field from eddy tracks and changes in the eddy characteristics.

55

Variability of the subtropical mode water in the Southwest Pacific Fernandez, Denise1, Sutton, Philip1, Bowen, Melissa2

Presenting author’s e-mail: [email protected]

1National Institute of Water and Atmospheric Research, Wellington, New Zealand 2University of Auckland, Auckland, New Zealand

Session 1.6 – February 8, 2018, 1715-1730

The variability of Subtropical Mode Water (STMW) in the Southwest Pacific is investigated using a 28 year-long time series (1986–2014) of high-resolution expendable bathythermograph data north of New Zealand (PX06) and a shorter time series, the Roemmich-Gilson monthly Argo optimal interpolation for the 2004–2014 period.

The variability in STMW inventories is compared to the variability in air-sea heat fluxes, mixed layer depths and transport of the East Auckland Current (EAUC, the subtropical boundary current north of New Zealand) to assess both the atmospheric and oceanic roles influencing the formation and decay of STMW.

Deeper mixed layers and negative anomalies in surface heat fluxes are correlated with increased inventories of STMW. The ocean heat content of the STMW layer is anticorrelated with inventories, particularly during the El Niño years. This suggests that large volumes of STMW are coincident with cooler conditions in the prior winter and with less oceanic heat storage. There is significant seasonal and interannual variability in STMW inventories, however there are no trends in STMW properties, including its core layer temperature over the last decade.

The variability of the winter EAUC transport is highly correlated with the STMW inventories and thermocline depth in the following spring, suggesting ocean dynamics deepen the thermocline and precondition for deeper mixed layers.

56

Direct observations of western boundary currents off northeastern Australia: seasonality and vertical structure Ridgway, Ken1, Benthuysen, Jessica2, Steinberg, Craig2

Presenting author’s e-mail: [email protected]

1CSIRO, Oceans and Atmosphere TAS, Australia

2AIMS ,QLD, Australia

Session 1.6 – February 8, 2018, 1730-1745

Boundary currents along the northern Australian coastal barrier provide the source waters of the East Australian Current (EAC) and also redistribute water to the equator within the Gulf of Papua Current (GPC). These currents are formed following the bifurcation of two Coral Sea westward jets, the North Vanuatu Jet (NVJ) and the North Caledonian Jet (NCJ). While the existence of the boundary currents has been inferred from limited geostrophic sections, gridded climatological analyses and modelling studies, no direct measurements of the absolute flow and transports of the EAC or GPC have been collected. Here we present cross-track velocities of these boundary currents that show their vertical structure, seasonal changes in direction and strength and spatial translation of the bifurcation location. We document the seasonal response of the boundary currents to the changes in the basin- scale wind stress curl to the east. The NVJ bifurcation varies seasonally about a latitude of 14°S; at peak northward extent in summer, the EAC and GPC exhibit maximum and minimum transports respectively. The deeper GPC component originating from the NCJ south of 18°S, also varies seasonally with an amplitude of 4-Sv. At 15.5°S its northward transport grows by ~ 5-Sv – the salinity signature of the glider data confirms that this influx is sourced from the northward turning inflow from the base of the NVJ. The full-depth transport confirms that the boundary currents respond along the entire boundary (18°-12°S) with a constant phase. Both the observed seasonal cycle of current strength and changes in along boundary transport are used to validate an ocean GCM. These results derive from a 7-year record of currents at Lizard Island and multiple glider deployments between 2010 and 2014. Both repeat glider transects at 14°S and 18°S and several deployments spanning latitudes between 18°-11°S were included in the study.

57

1.7 Sea-level science: from surface waves to global change Predicting extreme water levels around Australia Pattiaratchi, Charitha1,2, Hetzel, Yasha1,2, Janekovic, Ivica1,2

Presenting author’s e-mail: [email protected]

1School of Civil, Environmental, and Mining Engineering / UWA Oceans Institute, The University of Western Australia, WA, Australia 2Bushfire and Natural Hazards Cooperative Research Centre, VIC, Australia

Session 1.7 – February 8, 2018, 1445-1500

Throughout history, coastal residents have had to adapt to periodic coastal flooding. However, as a society we have become increasingly vulnerable to extreme water level events as our cities and our patterns of coastal development become more intricate, populated and interdependent. Impacts of extreme water level events along our coasts are increasing as populations continue to increase and mean sea levels rise. To better prepare, coastal engineers, managers and planners require a greater understanding of processes driving high water levels and their recurrence. Extreme water levels result from a combination of different physical processes including tides, storm surges, coastally trapped waves, wave set-up, tsunamis (from both seismic and meteorological origin), seasonal and inter- annual mean sea level variations. These signals may be forced by both local and remote forcing, with processes active over a temporal range from hours to decades. The timing of different processes is also critical as for example, a relatively small storm surge coinciding with high astronomical tides may have a different impact to a high storm surge coinciding with low water. Therefore it is very important that the exceedance probabilities of extreme water levels are predicted to inform flood and erosion risk-based management and for future planning. This study is aimed at estimating present day extreme sea level exceedance probabilities due to storm surges, tides and mean sea level (including wind-waves) around the coastline of Australia. A high resolution (~100m at the coastline) a hydrodynamic model was used to simulate water levels over a 60-year period. The model was validated using long-term tide gauge records. The time series water level data (at > 100,000 points) was to estimate exceedance probabilities around the coastline of Australia. A website has been developed to make the data available to the public.

58

Seasonal Sea-Level Patterns and Predictions around Australia Miles, Elaine1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Docklands, VIC 3008 AUSTRALIA

Session 1.7 – February 8, 2018, 1500-1515

A large proportion of Australia’s population and infrastructure is positioned by the coast, and vulnerable to current and future sea level rise. Over the last three decades, a combination of global sea level rise and natural variability has seen differing rates of change in sea level around Australia. Significant stretches of coastline have seen sea level rise that is well above the global average of 3.2 mm/year and some experience seasonal variability due to climate drivers, such as ENSO, at values up to 30 cm.

The early, tangible impacts of global warming often result from the interplay between the background trend and natural variability. For sea level, this takes the form of coastal erosion, damage to coastal infrastructure, contamination of ground water and salt water intrusion affecting agricultural land.

This research assesses the predictability of regional seasonal and inter-annual sea levels affecting Australian coastlines to provide context for sea level forecasts, such as storm surges. A preliminary evaluation of seasonal sea level forecasts using the Australian Bureau of Meteorology’s new seasonal prediction system ACCESS-S (Australian Community Climate and Earth-System Simulator – Seasonal) is presented. ACCESS-S uses the latest UK Met Office Global Seasonal 5 model, incorporating the most recent NEMO ocean model at a resolution of 25 km, to predict seasonal sea-level anomalies (SLA) with up to 6 months lead time. Using a dynamical model provides a distinct advantage over statistical models as it allows the prediction of SLA under unprecedented changes to physical forcings, such as climate change. The skill of ACCESS-S SLA deterministic and probabilistic regional forecasts is assessed using satellite altimeter data over the period 1993–2010 and tide gauge records.

This work will assist communities and emergency managers in assessing risks from future storm surges and sea level rise, and better prepare for those threats through improved planning and increased resilience.

59

Coupled wave climate and sea-level change during past analogues of tropical expansion Goodwin, Ian1, O’Leary, Mick2, Mitrovica, Jerry3, Ribo, Marta1

Presenting author’s e-mail: [email protected]

1Macquarie University, NSW, Australia 2Curtin University, WA, Australia 3Harvard University, MA, USA

Session 1.7 – February 8, 2018, 1515-1530

Instrumental observations of coastal sea-level and wave climate around Australia contain coupled variability associated with large-scale climate drivers; such as ENSO and the Interdecadal Pacific Oscillation (IPO) and Southern Annular Mode (SAM). A robust latitudinal and along-shelf gradient in storm and modal wave types (based on synoptic typology) and wave propagation patterns exists along the Southeast Australian Shelf (SEAS) (Goodwin et al. 2016) and along the Southwest Australian Shelf (SWAS) (Wandres et al. 2017 ). Future climate change projections indicate that the recent trend in the expansion of the latitudinal extent of the tropics in the south-west Pacific region will continue throughout this century. Trends in coastal behaviour along the North and Central Coasts of New South Wales since 1950 show a southward propagation of the onset of persistent shoreline recession and an anticlockwise rotation associated with a shift to more frequent tradewind swell and an associated slowing of longshore sand transport between coastal compartments.

The coastal impact of coupled sea-level, wave climate and sediment transport reversals during past periods of tropical expansion during 3,500 to 6,000 years BP and from 130,000 to 118,000 years BP are preserved in coastal strandplain archive around Australia. We report our progress in inverse modelling the timing and magnitude of relative sea-level rise and directional wave climate change during these past analogues of tropical expansion. A data assimilation-modelled paleoclimate reconstruction of sea-level , wind fields and ocean wave direction is presented for these periods of high sea-level during the past periods of tropical expansion. These results provide an important baseline to assess whether Global Climate Model projections of future wave climate change in response to tropical expansion are underdetermined.

References:

Goodwin, I.D., Browning, S., Mortlock, T.R., (2016). Tropical-Extratropical origin storm wave types and their influence on the East Australian Longshore Sand Transport System under a changing climate. J. Geophys. Res. Oceans, 121, 4833– 4853, doi:10.1002/2016JC011769.

Wandres, M., Pattiaratchi, C., Hetzel, Y., Wijeratne, E.M.S. (2017). The response of the southwest Western Australian wave climate to Indian Ocean climate variability. Clim. Dyn DOI 10.1007/s00382- 017-3704-z.

60

High-resolution sea level projections for the Australian region in the 21st century Zhang, Xuebin1, Church, John A.2, Monselesan, Didier1, McInnes, Kathleen L.3

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, TAS, Australia 2Climate Change Research Centre, University of New South Wales, NSW, Australia 3CSIRO Oceans and Atmosphere, VIC, Australia

Session 1.7 – February 8, 2018, 1530-1545

Sea level rise exhibits significant regional differences. Based on Coupled Model Intercomparison Project Phase 5 (CMIP5) models, sea level projections have been produced for the Australian region by taking account of regional dynamic changes, ocean thermal expansion, mass loss of glaciers, changes in Greenland and Antarctic ice sheets and land water storage, and glacial isostatic adjustment. However, these regional projections have a coarse resolution (~100 km), while coastal adaptation planners demand finer scale information at the coast. To address this need, a 1/10° near-global ocean model is set up to downscale ocean states for both the historical period and the 21st century projections of the ensemble average of 17 CMIP5 models under a high-emission scenario (RCP8.5). We produce high-resolution sea level projections by combining downscaled dynamic sea level with other sea level contributions such as melting of land ice. Off the southeast coast, dynamical downscaling provides better representation of high sea level projections associated with gyre circulation and boundary current changes. The high-resolution sea level projection should be a valuable product for detailed coastal adaptation planning (doi: 10.1002/2017GL074176).

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1.8 Ocean variability on timescales from days to decades Spectral descriptions of coastal submesoscale surface currents and passive tracers in an observational view Yoo, Jang Gon1, Lee, Eun Ae1, Kim, Sung Yong1

Presenting author’s e-mail: [email protected]

1Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Republic of Korea

Session 1.8 – February 7, 2018, 0930-0945

Submesoscale coastal surface currents and chlorophyll concentrations at hourly and O(1)-km resolutions, obtained from an array of high-frequency radars and geostationary ocean color imagery in a coastal region off the east coast of Korea over a period of one year (2013), are described in the frequency and wavenumber domains. The low-frequency surface currents exhibit more consistent variability with the regional geostrophic currents in summer than those in winter because of the relatively weak wind conditions and shallow mixed layer depths in summer. The clockwise near- inertial surface currents show onshore phase propagation and decreasing amplitudes associated with enhanced friction and reduced polarization due to the effects of the coastal boundary. The kinetic energy (KE) spectra of the surface currents in the wavenumber domain (k) become steeper at a scale of approximately 10 km from a slope of k-5/3 to slopes between k-2 and k-3 at a length scale of 2 km. Moreover, the KE spectra of the chlorophyll exhibit anisotropy associated with bathymetric effects and regional circulation, and their decay slopes change from k-5/3 to k-1 at O(10) km scales and from k-1 to k-3 at O(1) km scales, which is consistent with the two-dimensional quasi-geostrophic turbulence theory. The spectral decay slopes of these KE spectra show weak seasonality, which can be interpreted with the baroclinic instability in the weak seasonal mixed layer and the persistent and non-seasonal regional circulations.

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Intercomparison of Two Analogous Western Boundary Currents Archer, Matthew1,2, Roughan, Moninya1,2, Keating, Shane1, Lumpkin, Rick2, Shay, Lynn K.4, Beron-Vera, Francisco4

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2Sydney Institute of Marine Science, NSW, Australia 3Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, FL, United States 4Rosentstiel School of Marine and Atmospheric Science, University of Miami, FL, United States

Session 1.8 – February 7, 2018, 0945-1000

Western boundary currents (WBCs) are narrow, intense, poleward-flowing currents that form on the western side of every ocean basin. Because of their importance to the climate and ecology of some of the most densely populated coastlines on Earth, these currents have been a key focus of oceanographic observation programs. However, there have been very few intercomparisons of WBCs. Here, we use multi-year HF radar observations to study two major WBCs: the Florida Current in the North Atlantic and the East Australian Current in the South Pacific. These two WBCs meander at different timescales and amplitudes, resulting in very different mean jet profiles when averaged in regular geographical coordinates. By converting the data to a jet-following coordinate frame, the effect of meandering is removed, and we find that the mean structure of these WBCs is remarkably similar despite contrasting coastlines, bathymetry, and local wind forcing. These results show that despite differences in basin-to-basin variability of WBCs, in the mean they exhibit very similar relative vorticity regimes responsible for closing the major wind-driven ocean gyres.

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Characterisation and retention by East Australian Current meso-scale eddies: a Lagrangian approach Cetina-Heredia, Paulina1, van Sebille, Erik2, Roughan, Moninya1, Keating, Shane1, Brassington, Gary3

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2Utrecht University, Netherlands 3Bureau of Meteorology, NSW, Australia

Session 1.8 – February 7, 2018, 1000-1015

Meso-scale eddies are a dominant feature along the coast of southeast Australia significantly influencing the transport of water and water-borne particles. Consequently, they affect the distribution and supply of planktonic larvae to the coastline and thus, the replenishment of marine populations. This study uses Lagrangian tracking simulations of particles seeded within the East Australian Current (EAC) to examine eddies that originate as the EAC meanders and engulfs virtual particles. Particle trajectories are used to examine the characteristics of anticyclonic and cyclonic eddies (e.g. diameter, rotational velocities) and their potential to retain particles. Our results typify eddies in the region and highlight their effect on retention and likely impacts on transport. We find that particles are more likely to be retained within eddies with low eccentricity. In addition, particles typically reside inside cyclonic and anticyclonic eddies for a month and up to 4 and 9 months respectively. Thus, these flow structures are likely to influence water properties and impact larval dispersal and connectivity.

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Global Estimates of Mesoscale Mixing from High Resolution Sea Surface Temperature Satellite Data Groeskamp, Sjoerd1, Abernathey, Ryan2, Busecke, Julius2

Presenting author’s e-mail: [email protected]

1School of Mathematics and Statistics, University of New South Wales, NSW, Australia 2Department of Earth and Environmental Sciences, Columbia University, New York, USA.

Session 1.8 – February 7, 2018, 1015-1030

Mesoscale eddies stir, mix, and transport heat, salt and other (biogeochemical) tracers. This has significant consequences for the large-scale ocean circulation and influences the climate system a whole.

In this study, we use a decade worth of multiple high resolution (1 - 25 km) Sea Surface Temperature (SST) satellite data, to map and quantify mesoscale eddies by means of an Osborne-Cox diffusivity.

The Osborne-Cox diffusivity is obtained from the local SST variance budget. By studying the ratio between the local mixing length and the change in the background gradient, both of which are available from the SST data, we are able to make statements if the observed variance is dissipated locally or is instead advected in or out of the investigated local grid. This allows us to determine, where representing mesoscale mixing by means of an Osborne-Cox diffusivity is a valid.

This study is a big data approach, using observations to improve our understanding of, and ability to parametrize mesoscale mixing in numerical ocean modelling efforts.

65

Buoyancy driven ocean gyres Hogg, Andrew1, Gayen, Bishakhdatta1

Presenting author’s e-mail: [email protected]

1Australian National University, ACT, Australia

Session 1.8 – February 7, 2018, 1030-1045

One of the cornerstones of physical oceanography is the role of atmospheric winds in driving midlatitude gyres. These gyres are intensified on the western boundary of the ocean, giving rise to intense currents, such as the Gulf Stream, which play a major role in transporting heat around the globe. The physical mechanism used to account for wind-driven gyres is that the curl of the wind stress field adds potential vorticity to the upper ocean, which must be balanced by meridional transport in the ocean interior and a return flow close to the boundary. However, oceanic potential vorticity can also be modified by buoyancy fluxes, principally heating and cooling the ocean surface.

We examine the possibility that midlatitude gyres can be driven by surface buoyancy fluxes. The case is made using linear theory (a buoyancy-forced version of Sverdrup balance), using direct numerical simulation and a high-resolution, three-dimensional ocean model. The theory proposed here demonstrates that the midlatitude ocean gyres must balance with surface buoyancy fluxes as well as wind stress; thus, the strength of gyres (and their heat transport) will be directly modulated by surface warming as Earth’s climate changes.

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Temperature variability inshore of the Agulhas Current, from submesoscale to multidecadal Malan, Neil1,2, Backeberg, Björn3, Hermes, Juliet2, Reason, Chris1

Presenting author’s e-mail: [email protected]

1University of Cape Town, WC, 2South African Environmental Observation Network, WC, South Africa 3Council for Scientific and Industrial Research, WC, South Africa

Session 1.8 – February 7, 2018, 1045-1100

Ocean temperatures on the shelf regions between the Agulhas Current and the Southern African coast are strongly influenced by the interaction between upwelling events driven by the Agulhas Current itself, and those driven by upwelling and downwelling winds. Here, using a modelling approach along with several atmospheric reanalysis and observed wind products, we show that shelf temperatures are controlled at long, multi-decadal timescales by large scale latitudinal changes in the wind fields, linked to the Southern Annular Mode. Significant regime changes in temperature are observed in both the mid 1960’s and 1990’s, with the second shift being well observed for its effect on commercially important fish stocks. However, at shorter timescales, below the seasonal cycle, the Agulhas Current has a greater influence on the variability. Mesoscale meander events are examined using a composite approach in two different ocean models. Their interaction with the widening shelf promotes strong upwelling events, observed at over 100m/day, as well as an intensification of the vertical temperature gradient, which we suggest play an important role in driving thermocline variability on the shelf. Finally, instability on the inshore edge of the main Agulhas Current core produces submesoscale cyclones, which we hypothesise to have an important role in cross-shelf exchange, as well as transporting water and material to the nearby southern Benguela Current system.

67

Fine-scale satellite altimeter observations in the Southern Hemisphere: opportunities and challenges Morrow, Rosemary1

Presenting author’s e-mail: [email protected]

1LEGOS-CNRS/CNES/IRD/University of Toulouse III, Toulouse, France

Session 1.8 – February 7, 2018, 1130-1145

Satellite altimetry is undergoing a revolution in its ability to observe fine-scale ocean sea surface height (SSH) structures. Technology of alongtrack altimetric missions is changing, from conventional Ku-band Jason series to higher-resolution Ka-band Saral/AltiKa mission and Cryosat-2 and Sentinel-3 alongtrack SAR missions. Combined with improved data processing, these new data sets have lower instrument noise and better signal-to-noise at short wavelengths. We have estimated the noise levels from different altimeter missions using spectral analysis, and show how it varies geographically and seasonally. With Saral/AltiKa and Sentinel-3, we can now observe alongtrack ocean SSH signals with wavelengths down to 30-50 km, depending on the region and sea-state. The ocean’s wavenumber spectral slope also varies geographically and seasonally, reflecting the seasonal amplitudes of energetic mesoscales, (winter) sub-mesoscales, and internal gravity waves and internal tides.

This improved observation will be extended to global 2D SSH in 2021, when the NASA/CNES Surface Water and Ocean Topography (SWOT) 2D wide-swath altimeter will be launched. SWOT is designed to make the first global survey of Earth's terrestrial surface waters and the global and coastal ocean – at least twice every 21 days. SWOT’s Ka-band radar interferometer observes two swaths 60-km wide, with a nadir altimeter in the gap. The 2 km ocean grid is designed to resolve scales of 15-20 km, depending on the sea state. This offers an unprecedented opportunity to study finer-scale 2D SSH processes and the interaction of ocean circulation with ocean tides and internal gravity waves. However, the limited temporal sampling poses challenges to map the evolution of the ocean variability that changes rapidly at small scales. Opportunities and challenges of the mission will be presented for the Southern Hemisphere.

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Indian Ocean Dominance in Upper Ocean Heat Uptake since 2005: A global Perspective Rathore, Saurabh1,4, Bindoff, Nathaniel L.1,2,3,4, Phillips, Helen E.1,3, Feng, Ming2

Presenting author’s e-mail: [email protected]

1Institute for Marine and Antarctic Studies, University of Tasmania, TAS, Australia 2CSIRO Oceans and Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, Australia 3ACE CRC, University of Tasmania, TAS, Australia 4ARC Centre of Excellence For Climate Extremes, University of New South Wales, NSW, Australia

Session 1.8 – February 7, 2018, 1145-1200

The global oceans have absorbed 93% of the heat gained by Earth due to anthropogenic forcing. The warming of the ocean is not uniform, with more rapid warming occurring in the subtropical gyres of the Indo-Pacific basins. In this study, we use ensemble analysis of two different Argo datasets and four ocean reanalysis products during 2005-2015 to assess the temporal and spatial variations in the ocean heat content change. We find that the Indian Ocean is the most dominant basin of the global ocean heat uptake in the upper 700m during this period and has accumulated 73.8% of the global ocean heat gain increasing at the rate of (3.36 ± 0.81) × 1022 J/decade. Whereas, the Pacific Ocean has accumulated 26.8%, warming at the rate of (1.21 ± 1.52) × 1022 J/decade and the Atlantic Ocean has lost 6% of the global upper 700m heat content, cooling at the rate of (– 0.044 ± 0.84) × 1022 J/decade. Most of the Indian Ocean heat gain in 0-700m is stored in the subtropical gyre (around 40o S) and in the North Indian Ocean (0-30o N). Between 700-2000m, the Indian Ocean has absorbed 18.91% of global heat, warming by (0.79 ± 0.27) × 1022 J/decade. Large part of the heat gain in 700-2000m is distributed between the Atlantic (47.68%) and the Pacific Ocean (33.41%), which have warmed at the rate of (1.98 ± 0.47) × 1022 and (1.39 ± 0.30) × 1022 J/decade respectively. Decadal processes mostly control the rapid Indian Ocean surface warming while deep warming is attribute to the slower global warming. Better understanding of the temporal and spatial variability of warming patterns and the modes that drive them will constrain global climate models. This will improve the prediction of ocean warming and sea level rise in shorter ocean records.

69

Transport and energy conversion pathways along southeastern Australia (31.5- 34.5oS) Ribbat, Nina1, Roughan, Moninya1, Suthers, Iain1

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia

Session 1.8 – February 7, 2018, 1200-1215

Along and cross-shelf volume transports are key components in the distribution of nutrients, biota and materials across continental shelves. Along the coast of southeastern Australia transport has been studied through long-term mooring observations. However, the sparse spatial resolution of the sampling does not provide a complete picture of transport and exchange processes across the shelf. We configured a high resolution numerical model that captures both the mesoscale circulation offshore and the circulation across the continental shelf to characterize transport and energy conversion pathways off southeast Australia. Good agreements with observations show the skill of the model.Offshore the circulation in this region is dominated by its western boundary current, the East Australian Current (EAC) and its eddy field. However, our results show that the circulation regime inshore is not greatly affected by the EAC but driven by local dynamics and is consistent along-shore throughout the domain. Conversely, the middle and outer-shelf transport is mostly driven by the EAC and uncorrelated between regions upstream and downstream of the EAC separation zone.A transport budget shows that the EAC crosses the shelf break most likely between 31.5-32.5o S driving offshore transport and minimizing the occurrence of onshore transport. In contrast, between 34-34.5o S onshore transport is more typical. In addition, the strong poleward mean circulation induces large horizontal shear increasing the potential to develop barotropic instabilities. Thus, the barotropic energy transfer (MKE-EKE) is almost an order of magnitude higher than the baroclinic energy transfer (MPE-EKE). Our study identifies circulation regimes and sites of major water exchange across the shelf.

70

Frontal Eddies in the East Australian Current System Roughan, Moninya1,2

Presenting author’s e-mail: [email protected]

1University of New South Wales, Australia 2MetOcean Solutions, New Zealand

Session 1.8 – February 7, 2018, 1215-1230

With the advent of new technology, come new discoveries. It is only in recent years that we have we been able to observe and model small-scale features in the ocean. One example are the ~30km diameter cyclonic eddies that form along the inside edge of the East Australian Current System, known as Frontal Eddies.

We have used a range of new observations such as HF Radar and autonomous gliders combined with shipboard observations and ocean modelling to understand the genesis, dynamics, and evolution of these features. Through modelling studies, we have showed that frontal eddies have the capacity to entrain continental shelf waters, potentially laden with nutrients and shelf populations of larval fish. Using shipboard observations we have quantified the 3-Dimensional structure of a Frontal Eddy just 30km in diameter showing the first observational evidence of eddy tilting. Frontal eddies have the ability to grow to great depths (>1000m) rapidly (< 7 days). We also showed these eddies are extremely dynamic, ageostrophic and disproportionately productive. Using newly available high- resolution observations of surface currents from HF radar, we showed that local wind forcing is significant in the generation of Frontal Eddies and that they form every 1-2 weeks on the inside edge of the EAC. They are advected long distances (25-35km per day) and are more common than we thought. They also showed that Frontal Eddies have a significant impact on productivity with upwelling of 10s of m per day on their leading edge.

Enhancing our understanding of these previously unobservable small eddies is significant as it will lead to better model parameterisation, and an understanding of the role they play in the transport of heat, nutrient enrichment and their disproportionate contribution to biological productivity (compared to larger eddies) in what is a typically oligotrophic western boundary current regime.

71

Characterising the cross-shore variability of internal tides at 27.5°s off east Australia Queiroz, Eduardo1, Kerry, Colette1, Roughan, Moninya1

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia

Session 1.8 – February 7, 2018, 1230-1245

Internal tides can be responsible for mixing the ocean, surface convergences and near-bottom currents, therefore their predictability is of interest. They can modulate temperature, nutrient concentrations, and thus affect biological productivity. The characteristics of the internal tide and how it interacts with mesoscale ocean features along eastern Australia is still unknown. Using data from an array of deep ocean moorings, this study characterises the strength and variability of the internal tide, in both time and space, off eastern Australia (~ 27°S). Energy in the diurnal frequency band is greater than the semidiurnal energy. The internal tide variability is compared to the local tidal forcing and stratification to determine the influence of the ocean features. We investigate the interaction of the mesoscale flow field on the internal tide. The results reveal that the strength of the locally generated internal tide is modulated by the passing of cyclonic mesoscale eddies that change the local stratification. This is caused by uplift of the pycnocline by cyclonic eddies passing close to the coast. The results provide insight into the origin of the internal tides propagating onto the shelf and the mechanisms of variability. Studying the characteristics of internal tides and their interactions with the ocean features helps understand their variability and predictability, in contrast to the deterministic barotropic tides.

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Spatio-temporal Variations of Mesoscale Eddies in the Sulu Sea He, Yinghui1,2, Feng, Ming2, Xie, Jieshuo1, Liu, Junliang1, Chen, Zhiwu1, Xu, Jiexin1, Fang, Wendong1,3, Cai, Shuqun1,3

Presenting author’s e-mail: [email protected]

1State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, CAS, 164 West Xingang Road, Guangzhou 510301, China 2CSIRO Oceans and Atmosphere, Floreat, Western Australia, Australia 3University of Chinese Academy of Sciences, Beijing, 100049, China

Session 1.8 – February 7, 2018, 1245-1300

Mesoscale eddies have been observed in the Sulu Sea, but their characteristics have not been well described. This study investigates the eddy population in the Sulu Sea using 22 years of satellite altimeter data with high spatiotemporal resolution. On average, there are approximately 1.6 eddies observed in the Sulu Sea each day and 1.8 eddy tracks generated each month. Two of the main eddy genesis regions are west of Negros Island and the Zamboanga Peninsula. The mean radius, lifespan and propagation speed of the eddies are 76.6 km, 32 days and 4.5 cm/s, respectively. The eddy radius and amplitude are generally large in the central Sulu Sea but small on its margin. The mean eddy kinetic energy and vorticity generally monotonically decrease from south to north, consistent with the distributions of background current kinetic energy. Over the seasonal cycle, there are more cyclonic eddies during boreal winter, and they tend to have a larger amplitude and radius than the other 3 seasons, while there are more anti-cyclonic eddies during boreal summer, and they tend to have a larger amplitude and radius than the other 3 seasons. The instability of the mean current and the island gap wind jets are the two key eddy genesis mechanisms in the Sulu Sea.

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1.9 Advances in ocean modelling and prediction Surface drift and the search for MH370 Griffin, David1, Oke, Peter1, Jones, Emlyn1

Presenting author’s e-mail: [email protected]

1CSIRO, TAS, Australia

Session 1.9 – February 9, 2018, 0930-0945

In our 3rd (June 2017) report to the Australian Transport Safety Bureau, we nominated 35.6°S 92.8°E as the most likely location on the sea floor of the missing aircraft. What led us to this position? Eight clues, of very different nature, but all essential to the final estimate. CSIRO’s contribution to the search effort was drift modelling, i.e. simulating the dispersal of the buoyant debris resulting from the impact of the aircraft. This factored in the search in four ways: 1) steering the March-April 2014 surface search to where the debris may have drifted in those first few weeks, 2) back-tracking debris found in the western Indian Ocean to where it may have originated 500+days earlier, 3) identifying the few locations where the crash could have been and for no debris to come to Australia, and 4) backtracking the locations of objects identified in several Pleiades satellite photos to their location two weeks earlier. This work was all done using ocean modelling systems developed under Bluelink, which depended, in turn, on several streams of input data, the most crucial of which was arguably the sea- level observations made by satellite altimeters. In this talk we will discuss some of the oceanographic details and explain how the eight clues came together, emboldening us to nominate a position with a degree of confidence that far exceeded our initial expectations.

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Nested high-resolution atmosphere and ocean-4DVar assimilative system for the west coast of Australia Janekovic, Ivica1, Pattiaratchi, Charitha1, Hetzel, Yasha1, Grcic, Badema1

Presenting author’s e-mail: [email protected]

1School of Civil, Environmental, and Mining Engineering / UWA Oceans Institute, The University of Western Australia, WA, Australia

Session 1.9 – February 9, 2018, 0945-1000

The UWA ocean/atmosphere system is based on the latest WRF-ARW atmospheric model configured as a 2-way nested constellation consisting of 2 km resolution in the Perth region within a 10 km resolution covering the west coast. This system provides high spatial and temporal resolution forcing needed for the ocean counterpart. The hydrodynamic component is based on the latest ROMS 3D model, with curvilinear/stretched ~2.5 km (wide parent) and 500 m (nested Perth region) domain resolution, along with real-time forecast fields from Mercator and Hycom global models at the boundaries (acting as 2 independent model estimations). ROMS model was used in two modes: (I) 2- way coupled with atmosphere (via COAWST) providing SST feedback to the WRF model as well computing waves modified atmosphere-ocean boundary fluxes, and (II) using 4D-Var data assimilation capabilities with ~30 million observations used during a single month of simulation utilising NCIS Pawsey CRAY XC40 supercomputer. Reduced (without assimilation and atmosphere-ocean coupling) models have been running daily at UWA in near real-time mode for more than a year, providing stable 5-day 3D atmosphere/ocean forecasts with detailed outputs for the metropolitan region and major ports in WA. Acquisition and preparation of model inputs are fully automated, using open source shell and python environments partly developed at UWA. Comparison of model results with available sea level observations confirms that this system is capable of predicting even meteo-tsunami events that occur during winter frontal storms. Data from the system are freely available to the community via openDAP/thredds and plotted graphically on the web site (http://coastaloceanography.org).

75

Assimilation of Northwestern Tropical Pacific moored velocity data in a regional ocean modeling: Low frequency capabilities Danian, Liu1, Yeqiang, Shu1, Jiang, Zhu2

Presenting author’s e-mail: [email protected]

1State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China 2Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Session 1.9 – February 9, 2018, 1000-1015

The Northwestern Tropical Pacific Ocean (NWTPO) moorings observing system, including 15 moorings, was established in 2013 to provide velocity profile data. An Ensemble Optimal Interpolation (EnOI) is implemented for a Regional Ocean Modeling System (ROMS) to assimilate moored velocity profile data (October 2014–August 2015). The alternating zonal currents are the main characteristics of the upper circulation in the NWTPO, and the differences of zonal velocity between moorings and model outputs are mainly reflected in a low-frequency time scale (>90 days), which show a zonal flow- dependent large scale signal. Considering of the strong variations of the NWTPO circulation on multiple time scales, only 90-day low-pass-filtered zonal velocity without intraseasonal signals are assimilated into model to impove the simulation of position and intensity of currents. To match the low-frequency observation, the ensemble is low-pass-filtered with above 90 days and the instantaneous background fields are filtered in horizontal space. The signals of model outputs in the intraseasonal time scale are retained. Significant improvements are achieved for the simulation of position and intensity of the North Equatorial Current (NEC), the North Equatorial Countercurrent (NECC), and the Equatorial Undercurrent (EUC). More importantly, the temperature and salt fields can be reconstructed reasonably, and also the geostrophic balance can be well kept.

76

Observation impact from a regional reanalysis of the East Australian Current Kerry, Colette1, Roughan, Moninya2, Powell, Brian3

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2University of Hawaii at Manoa, HI, United States of America

Session 1.9 – February 9, 2018, 1015-1030

The use of Data Assimilation, whereby we combine a numerical model and oceanic observations, results in a more accurate ocean state estimate than either modelling or observations alone. In assessing system performance it is useful to know how each observation contributes to the solution and variational methods allow us to quantify this directly. We combine a numerical ocean model of the East Australian Current (EAC) region with an unprecedented observational data set, using 4- dimensional variational data assimilation, to generate a high-resolution ocean state estimate over a 2-year period (Jan 2012 - Dec 2013). Using this regional reanalysis we calculate the impacts of observations from various platforms in informing model estimates of volume transport in the EAC. The most influential observations are, in this order, the satellite derived SST, the radials from an HF radar array midway along the coast, the satellite derived SSH, the ocean glider observations and data from a full-depth mooring array in the northern, upstream portion of the domain. Not only do the HF radar observations have high impact on transport estimates at the array location, they have significant impact both up and downstream. Likewise, the impact of the mooring array is far reaching, contributing to transport estimates hundreds of kilometres downstream of its location. The observation impact of deep gliders deployed into eddies is particularly high. We find that observations taken in regions with greater natural variability are most impactful. Implications of the observation impact results are discussed. We confer what the results can tell us about the assimilation system design, such as forecast biases and prior choices of observation and background error covariances, and discuss how we might use the results to understand which observations are useful in informing model estimates, with the ultimate goal of tailoring observing system design to improve prediction.

77

Towards biogeochemical modelling of the East Australian Current system Rocha, Carlos1, Edwards, Christopher A.2, Kerry, Colette1, Roughan, Moninya1

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2University of California – Santa Cruz, CAL, U.S.A.

Session 1.9 – February 9, 2018, 1030-1045

The East Australian Current (EAC) is the Western Boundary Current of the South Pacific subtropical gyre and dominates the large scale flow of the Tasman Sea. It advects warm oligotrophic waters poleward, displacing cooler, generally more productive waters. It generates mesoscale eddies and induces coastal-upwelling. To better understand how this dynamic oceanographic regime influences the biogeochemical (BGC) properties of the EAC System, we have developed a coupled physical-BGC (ROMS+N2PZD2) model of the region. We strive to achieve a realistic simulation of the basis of the region’s marine ecosystem and to assess the variability of different biogeochemical variables. A high demand for this information exists, yet little is still known on how the specific dynamics of the EAC system define the region’s BGC processes. We evaluated the model's performance through comparison of chlorophyll-a model outputs with remote sensing products. We verified the model’s ability to reproduce the expected latitudinal differences in phytoplankton biomass and mesoscale dynamics - such as higher/lower concentrations in cold-core/warm-core eddies and upwelling filament formation – which was then used to categorise typical EAC eddies’ ecological value. These advances form the foundation for future work where we will explore specific scenarios including the BGC dynamics of cyclonic eddies, coastal entrainment and future climate change.

78

Numerical Experiments on Determining the Impacts of Channel Bends and Channel Bathymetry in Sydney Estuary Circulations, NSW Xiao, Ziyu1,2, Wang, Xiao Hua1,2,3

Presenting author’s e-mail: [email protected]

1The Sino-Australian Research Centre for Coastal Management, UNSW Canberra, Canberra, ACT, 2600, Australia 2School of Physical-, Environmental and Mathematical Sciences, UNSW Canberra, Canberra, ACT, 2600, Australia 3Sydney Institute of Marine Science Mosman, NSW Australia

Session 1.9 – February 9, 2018, 1045-1100

Sydney Harbour Estuary (in brief as Sydney Estuary) features a complex shoreline, a meandering main channel and varying bathymetry. Given the complex geometry of estuarine channels, both channel bends and channel bathymetry play an important role in driving lateral circulation which to a large extent impact on estuarine circulations. A fully calibrated three-dimensional hydrodynamic model in Sydney Estuary was utilized to conduct numerical experiment by smoothing channel depths, removing channel islands and straightening shorelines to determine the dominant forcing on regulating estuarine circulation under low river discharge condition during dry weather. Vorticity equation was adopted to study the generation and interplay of lateral and longitudinal circulation. In idealized flat and sinuous channel, the transformation of estuarine circulation momentum (- made a positive contribution to estuarine circulation during flood and made a negative contribution during ebb, which lead to a flood dominant tidal asymmetry. In idealized straight channel with lateral depth variations, the transformation of estuarine circulation momentum (- made a positive contribution to estuarine circulation during both flood and ebb, which lead to an ebb dominant tidal asymmetry. Since Sydney Estuary is an ebb dominant system, it can be demonstrated that channel bathymetry is the key feature in generating asymmetric lateral circulation thus amplified the estuarine exchange circulation.

79

The Horizontal Residual Mean: addressing the limited spatial resolution of models Yuehua, Li1, McDougall, Trevor1, Keating, Shane1, de Lavergne, Casimir1, Madec, Gurvan2

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2LOCEAN Laboratory, Universit’e Pierre et Marie Curie, Paris, France

Session 1.9 – February 9, 2018, 1130-1145

Horizontal fluxes of heat and other scalar quantities in the ocean are due to correlations between the horizontal velocity and tracer fields. However, the limited spatial resolution of ocean models means that these correlations are not fully resolved using the velocity and temperature evaluated on the model grid. We derive a method for estimating the horizontal flux due to spatially unresolved spatial correlations, based on calculating an additional non-divergent velocity to advect all scalar variables. The sum of the Eulerian-mean velocity and the extra advection calculated here we call the Horizontal Residual Mean velocity. The calculation of the extra advection is based on the depth-integrated horizontal transport from the sea floor to the density surface whose spatially averaged height is at the height of the calculation. In this way the Horizontal Residual Mean velocity has a similar interpretation to the Temporal Residual Mean velocity, with the former accounting for unresolved spatial correlations and the latter the unresolved temporal correlations.

80

Sensitivity of numerical ocean models to the choice of isopycnal mixing directions in rotated diffusion tensors Tailleux, Rémi1

Presenting author’s e-mail: [email protected]

1University of Reading, United Kingdom

Session 1.9 – February 9, 2018, 1145-1200

Despite considerable advances over the past 30 years, numerical ocean models still exhibit a number of systematic biases in their simulated properties even after their adjustable parameters have been optimally tuned to reduce discrepancies with observations, for instance by using an adjoint model as done by the MIT group. Optimization exercises carried out so far, however, all take it for granted that the isopycnal mixing directions in rotated diffusion tensors should be aligned with the so-called neutral directions. The physical basis for doing so, however, has never been satisfactorily explained from first principles. While it is generally agreed that neutral rotated diffusion succeeds in eliminating some of the spurious diapycnal mixing exhibited by early numerical ocean models mixing separately in the horizontal and vertical directions, there is little understanding of whether the use of the neutral directions is actually optimal to eliminate all unphysical diapycnal mixing. To shed light on the issue, this work examines the impact of the choice of isopycnal mixing directions on available potential energy (APE) and background gravitational potential energy (GPEr). In order to demonstrate its usefulness, we will first show that this approach succeeds in demonstrating the benefits of moving from a purely diffusive tensor mixing separately in the horizontal and vertical directions to a neutral rotated diffusion tensor combined with a eddy-induced parameterization. Prior such a move, APE was dissipated entirely by diabatic mixing, whereas in modern ocean models, APE is now primarily dissipated adiabatically by eddy-induced advection. The main effect of neutral rotated diffusion was to significantly reduce the diabatic dissipation of APE, as well as the diabatic generation of GPEr. Our work shows, however, that the neutral directions are not optimal to reduce these. The physics of these alternative mixing directions and implications for ocean modelling will be discussed.

81

ACCESS-OM2 Ocean-Ice Model: progress and plans Kiss, Andrew1, Hogg, Andrew1, Spence, Paul2, England, Matthew2, Heil, Petra3, Oke, Peter4, Hannah, Nicholas5, Fiedler, Russell4, Heerdegen, Aidan1, Munroe, James6

Presenting author’s e-mail: [email protected]

1Australian National University, ACT, Australia 2University of New South Wales, NSW, Australia 3Australian Antarctic Division & ACE CRC, University of Tasmania, TAS, Australia 4CSIRO, TAS, Australia 5Double Precision, NSW, Australia 6Memorial University of Newfoundland, Newfoundland, Canada

Session 1.9 – February 9, 2018, 1200-1215

COSIMA, ARCCSS and CSIRO are developing a global coupled ocean and sea ice model (ACCESS-OM2) at 1, 1/4 and 1/10 degree horizontal resolution. The model consists of the MOM5.1 ocean model, the CICE5.1 sea ice model, and a file-based atmosphere (JRA55 or CORE2) coupled via OASIS3-MCT. The 1-degree model is a development testbed that will also be useful for long-term ocean-ice experiments. The eddy-permitting 1/4-degree model will be used as a component of the next generation of the ACCESS coupled model (ACCESS-CM2). The eddy-resolving 1/10-degree model will inform the incorporation of sea ice into the OFAM3 component of Bluelink. The model is intended to be accessible and straightforward for new users to set up, run and analyse. The model development is public (see https://github.com/OceansAus/access-om2) and analysis tools are provided (http://cosima- cookbook.readthedocs.io). New users and contributors are welcome.

An overview will be given of the model configurations and the challenges faced in generating these configurations, followed by an assessment of model performance relative to observations. Comparisons will also be made with MOM coupled to the SIS sea ice model at 1/4 and 1/10 degree, and with the 1/10 degree near-global Bluelink.

82

Attributing contributions to spurious mixing in an Arbitrary Lagrangian-Eulerian ocean model Gibson, Angus1, Hogg, Andrew1, Kiss, Andrew1, Shakespeare, Callum1, Adcroft, Alistair2

Presenting author’s e-mail: [email protected]

1Research School of Earth Sciences and ARC Centre of Excellence for Climate System Science, Australian National University, Canberra, Australian Capital Territory, Australia 2NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA

Session 1.9 – February 9, 2018, 1215-1230

We examine the separate contributions to spurious mixing from horizontal and vertical processes in an ALE ocean model, MOM6, using reference potential energy (RPE). The RPE is a global diagnostic which changes only due to mixing between density classes. We extend this diagnostic to a sub- timestep timescale in order to individually separate contributions to spurious mixing through horizontal (tracer advection) and vertical (regridding/remapping) processes within the model. We both evaluate the overall spurious mixing in MOM6 against previously published output from other models (MOM5, ROMS, MITGCM and \MPAS), and investigate impacts on the components of spurious mixing in MOM6 across a suite of test cases: a lock exchange, internal wave propagation, and a baroclinically-unstable eddying channel.

The split RPE diagnostic demonstrates that the spurious mixing in a lock exchange test case is dominated by horizontal tracer advection, due to the spatial variability in the velocity field. In contrast, the vertical component of spurious mixing dominates in an internal waves test case. MOM6 performs well in this test case owing to its quasi-Lagrangian implementation of ALE. Finally, the effects of model resolution are examined in a baroclinic eddies test case. In particular, the vertical component of spurious mixing dominates as horizontal resolution increases, an important consideration as global models evolve towards higher horizontal resolutions.

83

The role of convection in driving geostrophic gyres and overturning circulation Gayen, Bishakhdatta1, Vreugdenhil, Catherine2, Griffiths, W. Ross1

Presenting author’s e-mail: [email protected]

1Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia 2DAMTP, Centre for Mathematical Sciences, University Of Cambridge, Cambridge, CB3 0WA, United Kingdom

Session 1.9 – February 9, 2018, 1230-1245

We use direct numerical simulations (DNS) to examine circulation forced by both wind- and buoyancy to model the North Atlantic circulation. Simulations are performed in a closed square basin. Half the base is cooled and the other half heated to achieve Rayleigh numbers Ra~1012, where Ra is defined in terms of the basin length L. Baroclinic Rossby number is Ro = 0.04, Prandtl number is Pr = 5 and Coriolis parameter is sinusoidal as on a spherical earth. Wind stress magnitude is varied. The results show that surface buoyancy forcing alone drives basin-scale subtropical and subpolar gyres along with full-depth overturning circulation. The results also show that circulation and heat throughput are governed by horizontal geostrophic flow in the thermal boundary layer, increasing with wind stress. Vertical heat transport from the surface layer into the deep interior mostly occurs in open-ocean chimney convection within the subpolar gyre. Net vertical transport of water is both in chimneys and against side boundaries. We calculate mechanical energy budgets at the buoyancy forcing currently feasible in DNS, the two energy sinks (dissipation and irreversible mixing) are largely confined to the thermal boundary layer.

84

Modelling Spectral Dissipation due to Wave Breaking for Ocean Wind Waves Model Performance for Light to Hurricane Wind Speeds Morison, Russel P.1, Banner, Michael L.1

1School of Mathematics and Statistics, The University of New South Wales, Sydney 2052, Australia

Session 1.9 – February 9, 2018, 1245-1300

In Banner and Morison (2010) we reported the development and performance of a saturation-based dissipation rate spectral source term, together with a complementary modeling framework that added wave breaking properties of the dominant wind sea to the usual suite of operational sea state forecast products. We report the performance of our further refined model framework for a wide range of wind speeds, from light to hurricane strength. Recent availability of new field data for wind and waves (including breaking waves) for very strong wind forcing conditions has allowed us to refine and verify our source terms and our methodology for forecasting breaking wave properties. We will present results showing that our source terms for wind input, nonlinear spectral transfer and dissipation, through wave breaking and background turbulence, allow the model to perform very stably over this wide wind-speed range without any retuning or use of limiters. The results also compare very favourably with observations of a strongly-forced evolving wind wave field at very short fetch. Overall, the wave model results described here conform very closely to a wide suite of performance indicators and the model is considered potentially suitable for adaptation within present operational applications and in future coupled atmosphere-ocean forecast models.

85

1.10 Oceans – general Fluorescence impact on Raman remote sensing of water temperature de Lima Ribeiro, Andrea1, Ajani, Penelope2, Derkenne, Caro1, Artlett, Christopher1,3, Pask, Helen1

Presenting author’s e-mail: [email protected]

1Macquarie University, NSW, Australia. 2University of Technology Sydney, NSW, Australia. 3Defence Science and Technology Group, NSW, Australia.

Session 1.10 – February 8, 2018, 1445-1500

Raman spectroscopy (RS) is based on the inelastic scattering of photons. In water, the scattering depends systematically on water temperature, and accordingly the Raman signal can be analysed to predict temperature with accuracy as high as ±0.1°C in pure (milli-Q) samples. In combination with LIDAR methods, RS offers a means of determining subsurface water temperature, extremely valuable in oceanographic studies. However, implementing such methods is challenging due to local variations in salinity, dissolved organic matter (DOM), phytoplankton density and particulate matter.

The Raman spectra of 10 sites around Sydney were measured (Enwave EZRaman-I dispersive spectrometer, spectral resolution of 8cm-1, 30mW excitation laser, 532 nm) and RMS temperature accuracies ranged from 0.1°C to 0.5°C. A Principal Component Analysis of the normalised spectra revealed that signals peaking around 580 nm and 680 nm accounted for a significant amount of variance between the locations, and can be associated with fluorescence from DOM and chlorophyll- a (chl-a), the latter of which is present in all phytoplankton species. To explore the extent to which fluorescence from chl-a might mask the water Raman signal, therefore, we carried out a controlled experiment in which we grew three species of phytoplankton and calculated the cell densities that produced fluorescence comparable to the Raman signal. These were found to include: Nannochloropsis sp. (9.14x103 cells.mL-1); Synechococcus Green (7.78x104 cells.mL-1); Synechococcus Red (1.23x105 cells.mL-1). These concentrations are found in the natural environment, indicating that the presence of chl-a fluorescence may compromise the accuracy of our method of water temperature prediction.

Our findings will help us to develop methods that are less susceptible to the presence of fluorescing matter, such as using an excitation wavelength where there is reduced overlap between Raman and fluorescence signals and baseline correction models.

86

The role of bottom-intensified mixing in an overturning circulation maintained by surface buoyancy forcing Stewart, Kial1, Landesman, Paul2

Presenting author’s e-mail: [email protected]

1Australian National University, Australia 2l’Ecole Centrale de Nantes, France

Session 1.10 – February 8, 2018, 1500-1515

Recently developed theories suggest that the observed enhancement of turbulent mixing nearing the seafloor has a leading order influence on the large-scale overturning circulation of the global oceans. These theories, while challenging established paradigms set by canonical oceanographers, are themselves challenging to verify by either observations or numerical models. This is because observations at the ocean bottom are scarce and the signals of interest are small, and ocean bottom processes are not directly simulated in numerical ocean models. Here, the role of externally imposed bottom-intensified mixing in an overturning circulation forced by differential surface buoyancy fluxes is examined with a laboratory experiment. The scientific insights and preliminary findings of these experiments are presented, and their implications discussed.

87

The influence of air-sea flux products, albedo and the depth penetrative effect of short wave radiation on upper ocean overturning circulation. Groeskamp, Sjoerd1, Iudicone, Daniele2

Presenting author’s e-mail: [email protected]

1School of Mathematics and Statistics, University of New South Wales, NSW, Australia 2Laboratory of Ecology and Evolution of Plankton, Stazione Zoologica Anton Dohrn, Naples, Italy

Session 1.10 – February 8, 2018, 1515-1530

Changing ocean inventories of heat and tracers such as carbon are central to climate change. As the ocean is vertically layered in density, the surface to interior pathways of tracers depend on density changes, in order to penetrate through those layers. The study of density changes, or `water mass transformation' (WMT), is therefore essential to understand and quantify the tracer pathways in the ocean.

Difficulties in accurately determining air-sea heat and freshwater fluxes, lead to large uncertainties in WMT rates, and the related ocean's (biogeochemical) tracer transport pathways

Here we quantify the uncertainties in observational based estimates of WMT rates, resulting from the use of different 1) air-sea flux products, 2) different shortwave radiation depth penetration parameterizations, 3) different albedo schemes. The results are presented as global WMT rates and their influence on the upper ocean overturning in different ocean basins and will provide insights into which processes, choices and parameterizations have significant influence on WMT rates.

88

Exploring the ocean response to anthropogenic aerosol forcing Irving, Damien1, Wijffels, Susan2, Church, John3, Bindoff, Nathan4

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, TAS, Australia 2Woods Hole Oceanographic Institution, MA, USA 3University of New South Wales, NSW, Australia 4University of Tasmania, TAS, Australia

Session 1.10 – February 8, 2018, 1645-1700

While well-mixed greenhouse gases (WMGHGs) are the primary driver of climate change in the industrial era, anthropogenic aerosols have also played an important role. As well as offsetting some of the radiative forcing associated with WMGHGs, the geographically distributed nature of anthropogenic aerosols means they can induce distinct regional patterns of change. The higher aerosol loading in the Northern Hemisphere is particularly important on a global scale, with previous studies identifying associated interhemispheric asymmetries in surface temperature and precipitation.

In order to explore the influence of anthropogenic aerosols on historical ocean change, we analyse data from the “anthropogenic aerosols only” single forcing experiment conducted as part of the CMIP5 project. While widespread ocean cooling is a consistent feature across the ensemble, the interhemispheric asymmetry in this cooling varies greatly. Analysis of the associated hemispheric energy budgets reveals that the primary cause of this model diversity is the surface energy response to the aerosol-induced asymmetrical radiative forcing. In particular, the partitioning of the response between upward latent heat flux, upward sensible heat flux and downward heat flux into the ocean is critical. It differs greatly among the ensemble and explains the diversity in modelled temperature trends very well. The upward latent heat flux (i.e. evaporation) is also an important factor in explaining the modelled salinity trends, however these are also influenced by precipitation changes related to the interhemispheric surface temperature gradient.

Given the challenges associated with observing surface energy fluxes, it has been difficult for the research community to establish the veracity of the historical CMIP5 simulations. Advances in this area would help greatly in understanding the degree to which interhemispheric asymmetries in observed ocean change are attributable to anthropogenic aerosol forcing.

89

Theme 2: Atmospheric Processes 2.1 Observations – Atmospheric, marine and remote The SWIO-TC Experiment: A field campaign to improve understanding and prediction of tropical cyclones and their impacts in the SW Indian Ocean Bousquet, Olivier1

Presenting author’s e-mail: [email protected]

1LACy, UMR 8105 (Meteo-France, CNRS, Reunion University)

Session 2.1 – February 8, 2018, 1100-1115

Tropical cyclones (TCs) are associated with heavy rainfall and strong winds that may cause huge human, material and environmental losses in many tropical and subtropical regions. This is particularly true in the southwest Indian Ocean (SWIO) basin, a poorly studied region that experiences a cyclonic activity roughly as intense as in the North-Atlantic basin. Over the last decades, a large number of storms have indeed caused devastations in , La Réunion, , Mozambique and other neighboring countries. In March 2017, TC Enawo and Dineo, caused for instance hundreds of fatalities and more than one million refugees in Madagascar and Mozambique, respectively.

The ability to collect high quality observations in and around tropical cyclones is essential to improve their representation in new high-resolution Numerical Weather Prediction (NWP) models currently being developed by most major Weather Services. This is all the more important in the SWIO basin where observation networks are extremely limited with, in particular, no routine aircraft observations and very sparse ground-based observations. One of the objectives of the EU-funded project ReNovRisk-Cyclones (2017-2020) is to overcome these shortcomings through strengthening permanent and temporary observation capabilities in this particularly active cyclonic basin.

This presentation will focus on the field phase of this collaborative, international, research program, which aims to assess the meteorological and oceanic impacts of TC on inhabited territories of the SWIO basin. This field experiment, referred to as the SWIO-TC Experiment, will be conducted in Jan- Apr 2019. It will provide unprecedented observations of tropical cyclones and other high impact weather events of the SWIO basin by coordinating dedicated atmospheric and oceanic measurements in the Mozambique Channel and Mascarene Archipelago. The current status, main scientific objectives and potential applications of this project will be discussed.

90

Polarsonde observations of clouds and aerosols in a Southern Ocean frontal passage Hamilton, Murray1, Mayo, Richard2, Hess, Marco2

Presenting author’s e-mail: [email protected]

1University of Adelaide, SA, Australia 2Atrad Pty Ltd, SA, Australia

Session 2.1 – February 8, 2018, 1115-1130

Cloud over the Southern Ocean is topical because observations and models disagree on both the overall level of cloudiness, and the amount of super-cooled liquid present in the clouds.

The polarsonde is a polarimetric backscatter sonde, launched with a radiosonde on a weather balloon, to profile the thermodynamic phase of cloud particles. We present here the results of three launches at Macquarie Is., on the 16th of Feb. 2017, spaced by four hours, as a cold front passed by the island.

The instrument generated profiles of both clouds and aerosols, with results to the cloud top being clearly interpretable, though those above the cloud top were affected by bright sunlight.

A surprise in the pre-frontal profile was that one cloud layer below the freezing level appeared to have non-spherical particles entrained with the cloud layer. This is evidenced by an enhancement of the cross-polarised signal, coincident with the enhanced co-polarised signal that indicates the cloud layer.

Other cloud layers at or below the freezing level were clearly comprised of liquid droplets. Glaciated or partly glaciated cloud layers were also observed up to about 6000 m. Detectable aerosols are present from the surface to at least 6000 m height.

The post-frontal profiles also showed low cloud below the freezing level with enhanced cross- polarised signal, but no obvious layering.

91

Comparison between Dobson and zenith-DOAS measurements of total ozone columns over Melbourne and an investigation of derivation algorithms Rhodes, Steve1, Tully, Matt1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 2.1 – February 8, 2018, 1130-1145

Instruments using the techniques of Multi-Axial Differential Optical Absorption Spectroscopy (MAX- DOAS) have chiefly been employed to study trace gases in the troposphere. Here, however, we present retrieved total ozone columns from zenith-pointing dawn and dusk measurements made over 18 months from Broadmeadows, a northern suburb of Melbourne. These total ozone columns are compared with those calculated from day time (not near dawn and dusk) measurements using a co- located Dobson spectrophotometer. Relative to the Dobson, the zenith-DOAS results are low by approximately 2.5 ± 2.5%. We resolve a previously seen difference between zenith-DOAS dawn and dusk total ozone columns. We also discuss the impact of different aspects of the respective algorithms for deriving total ozone columns, including the ozone cross sections used, the calculation of airmass, and assumptions regarding stratospheric temperature.

92

Forecast sensitivity to observations in ACCESS numerical weather prediction Tingwell, Chris1, Soldatenko, Sergei1, Steinle, Peter1, Kelly-Gerreyn, Boris1, De Maid, Robert1, Lane, Agnes1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 2.1 – February 8, 2018, 1145-1200

The Australian Community Climate and Earth System Simulator (ACCESS) provides the Australian Bureau of Meteorology with a suite of Numerical Weather Prediction (NWP) systems that incorporate 4DVar data assimilation and forecast model components developed by the UK Met Office and adapted for local use by the Bureau's Science to Services program. Meanwhile, the significant investment by the Bureau of Meteorology in the national observing network, and the constant evolution of observational technologies, require an ongoing assessment of the value of the network components.

Since NWP is one of the major mechanisms for converting observed data into information and services, an objective measure of the impact of each assimilated observing system on the quality of short-term ACCESS forecasts can potentially guide decisions related to network efficiency and effectiveness. Traditional techniques for assessing the impact of observations in NWP are both inflexible (in that they require dedicated trials) and computationally expensive, but a relatively new technique known as adjoint-based Forecast Sensitivity to Observations (FSO) is able to provide forecast impact information continuously, flexibly, and in real-time.

The Met Office version of the FSO technique has been implemented in conjunction with the operational ACCESS global NWP system (ACCESS-G) and a project, jointly sponsored by the Bureau's Science to Services and Observing Systems & Operations Programs, aims to develop the use of FSO to guide and inform observing network planning and assessment activities, aided by useful and informative analysis and visualisation tools.

The ACCESS-G FSO suite has now been running for two years and we have completed several assessments of the forecast sensitivity of ACCESS-G to the various components of the Global Observing System, and to particular components of the Australian observing network. A number of observation impact comparisons will be presented and we will also discuss plans for further work.

93

Three dimensional tomographic reconstruction of rainfall using satellite signals Huang, David Defeng1, Shen, Felix Xi1, Tang, Xiaowen2

Presenting author’s e-mail: [email protected]

1The University of Western Australia, WA, Australia 2Nanjing University, Jiangsu, P. R. China

Session 2.1 – February 8, 2018, 1200-1215

Today three rainfall measurement methods are widely in use: they are rain gauge, weather radar, and weather satellite. The path loss of microwave signals due to rainfall, known as rain attenuation, can also be used to measure rain. To this end, researchers have successfully employed rain attenuations of backhaul microwave links of commercial terrestrial cellular communication systems to reconstruct rainfall.

We propose to employ the rain attenuations of the microwave communication links of existing low earth orbit (LEO) and/or medium earth orbit (MEO) satellites to reconstruct rainfall. Specifically, with multiple satellite ground receivers and/or multiple LEO/MEO satellites, similar to using X-ray to carry out human-body Computerized Tomography (CT) scans, we propose to use the microwave signals of LEO/MEO satellites to achieve three-dimensional (3D) tomographic reconstruction of rainfall. Along with the deployment of LEO satellite constellations for global mobile satellite communication services (e.g. the OneWeb satellite constellation), in the future, the proposed tomographic approach may be implemented with low cost small-size satellite receivers to achieve 3D rainfall reconstruction anywhere on the planet.

Using synthetic data produced by the simulation of satellite microwave signals through an ideal supercell with the Weather Research and Forecasting (WRF) Model, we found that the proposed tomographic approach has distinct advantages. First, compared with weather radars and weather satellites, the proposed approach can be much cheaper, as microwave signals from existing satellites can be employed for free and only passive ground receivers are needed. Second, compared with rain gauges that are scattered on the Earth, the proposed approach can achieve continuous measurements in space. Third, compared with using commercial terrestrial cellular communication systems, which can only achieve 2D rainfall reconstruction, the proposed approach can achieve 3D rainfall measurements.

94

The Australian Wind Profiler Network for Operations and Research Dolman, Bronwyn

Session 2.1 – February 8, 2018, 1215-1230

Between 2011 and 2017, the Australian Government Bureau of Meteorology installed a network of 9 wind profiling radars (WPRs) across Australia. There are two WPR classes, with Boundary Layer (BL) Profilers in Ceduna, Mildura, Cairns, Coffs Harbour and Mackay, and Stratospheric Tropospheric (ST) Profilers in Halls Creek, Tennant Creek, Carnarvon and Longreach. These systems complement an existing network of 5 Bureau profilers installed at Sydney, Launceston, Canberra, Broadmeadows and East Sale, which underwent software and minor hardware upgrades. In addition to the operational Bureau network, ATRAD Pty Ltd, the University of Adelaide, the Australian Antarctic Division and Mt Isa Mines operate profilers in Adelaide, Davis Station in Antarctica, and Mt Isa, respectively, representing a network of 18 instruments across Australia.

Data from the operational network are used directly by Bureau forecasters, and are broadcast on the GTS for ingestion into Australian and global Numerical Weather Prediction (NWP) models. The network is used for research studies into areas such as precipitation. The Adelaide Airport site is of particular interest, as it is within the scanning footprint of the Buckland Park Weather Watch radar, which has recently been upgraded to dual polarisation. Profiler and weather watch retrievals of the rainfall drop size distribution can thus be compared and contrasted in the vertical column above the site, and the technique can potentially be applied at other profiler sites around Australia.

This talk will introduce the Australian Wind Profiler network, and present investigations into the use of its data in global numerical weather prediction models. Results from the Australian Community Climate and Earth-Systems Simulator (ACCESS), and precipitation retrievals from Adelaide Airport will be featured.

95

2.2 Atmospheric and oceanic chemistry in the earth system: insights from the Southern Hemisphere Biomass Burning Emissions in the Southern Hemisphere Wiedinmyer, Christine1

Presenting author’s e-mail: [email protected]

1University of Colorado Boulder, Boulder, Colorado, USA

Session 2.2 – February 9, 2018, 0930-0945

Globally, biomass burning (which includes wildland and bush fires, controlled burns, land-clearing and agriculture fires) is an extremely important source of atmospheric pollutants, including particulate matter and reactive trace gases such as carbon monoxide and volatile organic compounds. In the Southern Hemisphere, biomass burning dominates over all other atmospheric pollutant sources. Biomass burning emissions can impact air quality and climate, and have influence reaching from populated areas to remote regions and from the surface to well into the upper troposphere.

Satellite observations can be used to identify the inputs to fire emissions models that predict the timing, location and magnitude of pollutant emissions from biomass burning. The Fire INventory from NCAR (FINN) uses a combination of key satellite observations, laboratory studies and in-situ field measurements to estimate daily, global pollutant emissions from open biomass burning. To date, emissions from 2002 to the present have been calculated. These emissions are used to explore the variability and impacts of biomass burning across the Southern Hemisphere.

Despite great advances in the ability to identify and quantify emissions from biomass burning, the techniques used to predict emissions and understand their fate and transport in the in the atmosphere are uncertain, and the subsequent estimates of the impacts are difficult to assess. Global change driven by climate, policy, and social behaviours alter fire activity and its impacts. Quantification of the feedbacks and interactions between fire activity and global change remain critical open questions. This presentation will detail efforts to identify and quantify biomass burning emissions across scales, and highlight their importance and confounding factors in air quality, health, and climate impact assessments.

96

Characterising terrestrial influence in the remote Southern Ocean Chambers, Scott1, Williams, Alastair1, Griffiths, Alan1, Preunkert, Susanne2

Presenting author’s e-mail: [email protected]

1Australian Nuclear Science and Technology Organisation, NSW, Australia 2Centre National de la Recherche Scientifique, St. Martin d'Hères, France

Session 2.2 – February 9, 2018, 0945-1000

The ability to characterise “baseline” trace species concentrations in the remote marine boundary layer of the Southern Ocean, and thereby better constrain the magnitude and distribution of incursions of anthropogenic pollutants, is contingent upon a comprehensive understanding of direct and indirect terrestrial influences. Continued expansion of the international network of radon detectors for long-term monitoring in the Southern Hemisphere, as well as the recent installation of an ANSTO dual-flow-loop two-filter radon detector aboard the CSIRO Research Vessel Investigator, is bringing meteorologists and chemists alike a few steps closer to this nirvana.

Between January 2015 and March 2017 the RV Investigator completed 5 Southern Ocean transects between 50°-180°E. Although “baseline air” (222Rn≤45 mBq m-3) was frequently encountered, three persistent features of interest were identified: (i) enhanced radon within the region 50-55°S (likely attributable to vestigial terrestrial influence of synoptic transport origin), (ii) radon enhancement in the vicinity of the polar front (likely attributable to synoptic-related tropospheric subsidence events), and (iii) increasing radon concentrations in the immediate vicinity of the Antarctic coastline (attributable in part to enhanced radon concentrations in tropospheric subsidence related to Antarctic katabatic drainage events).

The recent development of a simple experimental technique to separate katabatic, oceanic and local/coastal Antarctic air masses more effectively than achieved via back trajectory analysis has provided clear experimental evidence of significant, seasonally-varying, terrestrial influence in the Antarctic troposphere south of Australia, which has implications for the indirect transport of nutrients and pollutants to this remote continent. The distribution (10th/50th/90th percentiles) of Dumont d’Urville radon concentrations in summertime oceanic air masses was 4/18/47 mBq m-3, and 8/30/86 mBq m-3 in katabatic events, with peak katabatic values of 230 mBq m-3. The ability to separately characterise trace constituent concentrations in tropospheric, marine, or locally-sourced air masses stands to greatly enhance Antarctic process studies.

97

Comparison of mid-latutude springtime ozone in northern and southern hemispheres Tully, Matt1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Victoria, Australia

Session 2.2 – February 9, 2018, 1000-1015

Inter-annual variability in mid-latitude ozone is dominated by the magnitude of the build-up of ozone over winter and spring in each year. Using the cohesive SBUV dataset developed by NOAA, we find that springtime zonal mean ozone values are well-correlated across a range of latitudes from 20° to 50° in both hemispheres, and strongly anti-correlated with winter tropical values, defined as 10°S- 10°N. The same relation holds between the high-frequency and low-frequency components of these bands, implying that most of the long-term difference between the hemispheres can be explicitly accounted for as dynamical variability, and therefore largely removed by forming a weighted mean of tropical plus mid-latitude ozone in each hemisphere. The resulting weighted mean time-series for both hemispheres closely follow stratospheric chlorine concentration with an additional contribution from the 11-year solar cycle.

98

A new scheme for dry deposition of ozone to the ocean and its impact on global deposition budget Luhar, Ashok1, Woodhouse, Matthew1, Galbally, Ian1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Vic, Australia

Session 2.2 – February 9, 2018, 1015-1030

Ozone (O3) is formed in both the stratosphere and the troposphere by photochemical reactions involving natural and anthropogenic precursor species. Ozone acts as a greenhouse gas, and adversely impacts human health and plant productivity. It has the third largest global warming effect after CO2 and methane, and thus plays an important role in the Earth's climate system. The tropospheric ozone burden has increased by about 40% since preindustrial times as a result of increases in the emissions of ozone precursors. Dry deposition at the Earth's surface is an important sink of ozone, which influences ozone concentration as well as its lifetime and long-range transport. Past modelling studies suggest that ozone deposition to water is about one-third of the total deposition, and has the largest uncertainty compared to other surface types. We evaluate existing approaches for ozone deposition to the ocean within the ACCESS-UKCA global climate-chemistry model, and develop a new mechanistic scheme that involve all the relevant waterside processes including ozone solubility, molecular diffusion, turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. The new scheme is compared with deposition velocity measurements, and its impact on the global deposition budget is quantified.

99

Aerosol and cloud profiling with surface-based lidars Alexander, Simon1

Presenting author’s e-mail: [email protected]

1Australian Antarctic Division, Hobart, Australia

Session 2.2 – February 9, 2018, 1030-1045

Recent land and ship-based Southern Ocean campaigns have provided a wealth of data from lidars. Surface measurements are only now beginning to be made in this region, yet are required to provide basic climatological parameters in order to validate models and evaluate satellite retrievals. From the backscattered signal received by the lidar, properties of clouds and aerosols may be readily determined. Lidars provide a powerful ability to resolve the vertical structure of aerosols in the troposphere and the ability to examine its temporal evolution. As such, lidar-resolved aerosol information provides complementary information to that gleaned from co-located surface measurements. We will use data obtained from Macquarie Island and onboard R/V Investigator to quantify the vertical properties and structure of aerosol events present in the lower troposphere. We will discuss these aerosol results in the context of cloud formation and occurrence.

100

Radiation, cloud and precipitation response to global perturbations of dimethyl sulfide Fiddes, Sonya1,2,3, Woodhouse, Matthew3, Lane, Todd2, Schofield, Robyn2

Presenting author’s e-mail: [email protected]

1Australian-German Climate and Energy College, University of Melbourne, Parkville, Australia 2ARC Centre of Excellence for Climate System Science and the School of Earth Sciences, University of Melbourne, Parkville, Australia 3Climate Science Centre, Oceans and Atmosphere, Commonwealth Scientific and Industrial Research Organisation, Aspendale, Australia

Session 2.2 – February 9, 2018, 1045-1100

The global radiation budget is significantly impacted by uncertainties in natural aerosol. Dimethyl sulfide (DMS), produced by marine organisms, makes up approximately one fifth of the global sulfur budget and can influence aerosol and cloud formation, radiation and the global climate more generally. Current understanding of DMS concentrations and its processes once in the atmosphere are limited. Recent literature indicates that oceanic DMS concentrations may be greater than we currently realise, especially in coral reef regions. In this study, the Australian Community Climate and Earth System (ACCESS) - United Kingdom Chemistry and Aerosol (UKCA) global climate-chemistry model is used to gain better insight into the role DMS plays in our climate. Three experimental simulations are compared to a control simulation: a zero marine DMS simulation, a zonally enhanced DMS simulation and simulation in which coral reef derived DMS is included for the first time. The zero DMS and zonally enhanced DMS simulations both yield large differences in global aerosol, though of opposite signs. Interestingly, changes in cloud cover, radiation and precipitation are limited to regions where stratiform cloud decks form in the eastern ocean basins of the Southern Hemisphere. These regions are poorly captured by ACCESS-UKCA and other global climate models and indicate a particular sensitivity of these regions to changes in DMS. Furthermore, preliminary results investigating whether the inclusion global coral reef derived DMS in the ACCESS-UKCA has an impact on global or regional climate will be presented.

101

Improved understanding of biogenic emissions, chemistry and impacts in Southeast Australia Fisher, Jenny A.1, Greenslade, Jesse W.1, Kettlewell, Graham1, Palmer, Paul I.2, Surl, Luke2, Paton- Walsh, Clare1, Guerette, Elise-Andrée1

Presenting author’s e-mail: [email protected]

1Centre for Atmospheric Chemistry, University of Wollongong, NSW, Australia 2National Centre for Earth Observation, University of Edinburgh, United Kingdom

Session 2.2 – February 9, 2018, 1130-1145

Southeast Australia is a global hotspot for biogenic emissions of isoprene and monoterpenes, as indicated by both process-based emission models and satellite observations of formaldehyde (a high- yield isoprene oxidation production). However, existing in situ measurements of biogenic species and their oxidation products are sparse in this region, leading to large uncertainties in both emissions and the ensuing chemistry. These uncertainties hamper our ability to accurately predict ozone and organic aerosol formation, with implications for understanding air quality in populated areas near biogenic sources such as the Sydney basin. In this talk, we will describe two related projects designed to better quantify Australian isoprene emissions and evaluate their chemical impacts. For the first, we use a global chemical transport model (GEOS-Chem) combined with formaldehyde observations from the OMI satellite instrument to derive top-down estimates of isoprene emissions that cover the entire Australian continent with monthly temporal resolution. We then leverage the new understanding of biogenic chemistry that has resulted from recent large-scale measurement campaigns in the Southeast US to better understand the impacts of Australian biogenic emissions. We implement this new chemical understanding in a ~25 km-resolution nested version of the GEOS-Chem model for the Australian continent. We use the model to predict formation of ozone, organic aerosol, and other compounds from biogenic emissions in Southeast Australia, and to contrast these to their production in the Southeast US where the emissions profile is very different. Finally, we compare our model predictions to existing in situ measurements (where available) to highlight remaining uncertainties in biogenic emissions and chemistry that should be targeted by future measurement campaigns.

102

Aliphatic Aldehydes as Photolytic Sources of H2 in the atmosphere Harrison, A.W.1, Kharazmi, A.1, Shaw, M.F.2, Jordan, M. J. T.2, Kable, S. H.1

Presenting author’s e-mail: [email protected]

1University of New South Wales, Sydney, Australia 2University of Sydney, Sydney, Australia

Session 2.2 – February 9, 2018, 1145-1200

Molecular hydrogen is regarded as a potential replacement for hydrocarbons as a clean and renewable energy source providing motivation for efficient, large-scale production of H2. This will likely lead to H2 leakage into the atmosphere which is important as H2 is an indirect greenhouse gas and impacts tropospheric concentration of OH and O3.1 A full accounting of the atmospheric H2 budget is therefore of fundamental interest in the future H2 economy. Currently, the major known sources of H2 in the atmosphere are formaldehyde (H2CO) photodissociation, fossil fuel and biomass combustion, and biogenic emission.2 However, the present knowledge of H2 sources and sinks is qualitative, and it has been suggested that additional H2 production arises from photolysis of larger aldehydes which is unaccounted for.

We have recently made the first experimental observation of a photodissociaton channel of acetaldehyde leading to formation of ketene (CH2CO) and hydrogen (H2). This was accomplished using two complimentary experimental techniques. The H2 photofragment was investigated utilizing a velocity-map imaging (VMI) apparatus, while the quantum yield of ketene production was characterized following acetaldehyde photolysis in a FTIR gas cell. With the velocity-map imaging results, we provide a detailed investigation of the photodissociation dynamics of this product channel while the FTIR results allow us to determine the quantum yield of this process under atmospheric conditions. In addition, using these methods, we have evidence for photolytic production of H2 from other aldehydes including propanal, isobutanal, butanal, and 2-methylbutanal which have low barriers to H2 production via triple fragmentation dissociation pathways. This work provides evidence for H2 being a general photoproduct from aldehydes which are currently not included in atmospheric models.

103

Statistical modelling of airborne grass pollen Silver, Jeremy1, Sims, Holly2, Bannister, Tony2, Ebert, Elizabeth2, Newbigin, Edward1, Haberle, Simon3, Graham, Bruce4

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia 2Australian Bureau of Meteorology, NSW, Australia 3Australian National University, ACT, Australia 4Charles Sturt University, NSW, Australia

Session 2.2 – February 9, 2018, 1200-1215

The thunderstorm asthma event in Victoria on the 21st November 2016 has mainly been attributed to the confluence of extreme grass pollen levels and a dramatic gust front. The response from the Victorian Government has included a project to establish an epidemic thunderstorm asthma risk warning system, currently under development by a consortium involving the Bureau of Meteorology, the Victorian Department of Health and Human Services, the CSIRO and five Australian universities. In addition to new pollen monitoring sites around Victoria, forecasts of daily grass pollen levels will be based on manual forecasting techniques, dispersion modelling and statistical modelling. This talk presents the development and preliminary results of the statistical model for grass pollen in South- Eastern Australia.

The model was trained on pollen counts from the University of Melbourne, and considered not only widely available meteorological variables (e.g. temperature, humidity), but also soil dryness and drought indices. Forward-variable selection by cross-validation was performed, with non-linear effects being allowed through the use of Generalised Additive Models (GAMs). The model shows moderate skill (out-of-sample R2 between 0.6 and 0.8), and is considerably more accurate than either persistence or climatology; categorical forecasts (i.e. low/medium/high) are comparable with those of day-ahead manual forecasts from the Melbourne Pollen Count.

We will present a summary of the model validation on historical data, and a validation of the model for the Victorian grass pollen season 2017 (October-December); this period represents the first test of a pilot thunderstorm asthma risk warning system.

104

The importance of the ground state in the atmospheric photochemistry of carbonyls Corrigan, Maggie E.1, Nikoobahkt, Behnam1 Kable, Scott H.2, Jordan, Meredith J. T.1,3

Presenting author’s e-mail: [email protected]

1School of Chemistry, The University of Sydney, NSW Australia 2School of Chemistry, University of New South Wales, NSW, Australia 3Current address: School of Chemistry, University of New South Wales, NSW, Australia

Session 2.2 – February 9, 2018, 1215-1230

Tropospheric chemistry is driven by the absorption of actinic radiation with wavelengths >290 nm and carbonyl photolysis an important source of radicals in the troposphere. Carbonyls, such as formaldehyde, acetaldehyde and acetone, are abundant in the troposphere from primary anthropogenic and biogenic sources as well as being secondary oxidation products. The carbonyl C=O functional group absorbs actinic radiation with an n * transition to the first excited electronic state S1. This can then relax to the first excited triplet state, T1, or the ground state, S0. Whilst acetone can dissociate to form radicals on S1, the formaldehyde and acetaldehyde S1 states are bound and any dissociation must occur on T1 or S0. It has been previously assumed that excited state chemistry dominates the photochemistry of carbonyls. Recent work in the group, however, has demonstrated the importance of S0 reactions in carbonyl photochemistry, although little is known about how the electronically excited molecules relax to S0. Here we model intersystem crossing (ISC) S1 T1 S0 using MRCI-F12/SA-MCSCF/aug-cc-pVDZ electronic structure theory calculations of the energies of these states and the spin-orbit couplings between them, together with reduced dimensional MCTDH calculations to determine ISC rate coefficients. These results show ISC to S0 in acetone is relatively slow and excited state chemistry dominates. In contrast, in formaldehyde and acetaldehyde, ISC to S0 is fast and competitive with dissociation on T1 and deactivation by collisions with N2 (or O2). Thus it is important to consider ground state mechanisms in the photolysis of these molecules when considering their atmospheric fate. Implications of these mechanisms to the atmospheric chemistry of formaldehyde, acetaldehyde and other atmospherically relevant carbonyls will be discussed.

105

Grass pollen dispersion modelling in SE Australia with the CSIRO-CTM: Preliminary results Silver, Jeremy1, Emmerson, Kathryn2, Ebert, Elizabeth3, Wain, Alan3, Cope, Martin2, Newbigin, Edward1

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia 2CSIRO Marine and Atmospheric Research, VIC, Australia 3Australian Bureau of Meteorology, VIC, Australia

Session 2.2 – February 9, 2018, 1230-1245

Allergy to grass pollen (especially from rye grass) is understood to trigger hay fever and even asthma in many Australians. Recent episodes of thunderstorm asthma (especially that of November 2016 in Victoria) are largely attributed to the interaction of pollen and low level convergence such as is found in thunderstorm gust fronts. In response to this, a thunderstorm asthma warning system to support the Victorian Department of Health and Human Services (DHHS) in alerting the community and health and emergency response sectors is being developed by a consortium involving the Bureau of Meteorology, the DHHS, the CSIRO and five Australian universities. Part of this involves the development of a grass pollen dispersion model.

The CSIRO-CTM (Chemical Transport Model) has been modified to emit and advect a single aerosol species, namely grass pollen. The pollen emissions module relies on detailed land-use information, pollen season curves and local micrometeorology (e.g. wind speed, temperature, humidity).

We will present preliminary results, including a pre-operational trial spanning Victorian grass pollen season 2017 (October-December), and simulations of the 21st November 2016 thunderstorm asthma event in Victoria. Model results will be compared with pollen observations from the expanded pollen monitoring network in Victoria.

106

Ocean – Atmospheric interaction studies using 11 year CALIPSO Lidar measurements Hu, Yongxiang1, Xu, Kuanman1

1NASA Langley Research Center, Hampton, VA 23681, USA

Presenting author’s e-mail: [email protected]

Session 2.2 – February 9, 2018, 1245-1300

Currently, ocean carbon biomass is estimated from ocean color measurements primarily through particulate backscatter coefficients (bbp). Small non-algal particles contribute significantly to bbp due to the fact that small particles scatter more isotropically while bigger particles scatter mostly in the forward direction. CALIPSO’s ocean subsurface cross polarization measurements (Figure 1) are not sensitive to small particles far less than 2 micron in size since these particles rarely cause depolarization. Thus cross polarization backscatter is contributed mostly by larger, depolarizing phytoplankton particles. This is why CALIPSO’s cross polarization has much larger contrasts comparing with MODIS reflectance (CALIPSO cross polarization is very weak in Gyres and much stronger in high latitudes, See figure 1). CALIPSO cross-polarization measurements in the Southern Oceans also suggest that water cloud droplet number concentration co-varies with phytoplankton carbon biomass (Figure 2), but it has less correlation with particulate organic carbon (POC) (Figure 2) and chlorophyll concentration. The study also agrees with water cloud droplet size retrieved from Parasol’s polarization measurements.

Figure 1. Left panel: CALIPSO ocean subsurface cross polarization signal. Right panel: equivalent CALIPSO ocean subsurface co-polarization signal derived from MODIS 531nm measurements.

Figure 2. Left panel: Anomaly of CALIPSO cross polarization ocean subsurface (red) and water cloud (blue) measurements in the Southern Oceans. Right panel: anomaly of MODIS particulate organic carbon (POC) (phytoplankton and non-algal particles) (blue line) vs CALIPSO cross polarization (mostly phytoplankton) (red line) measurements.

107

2.3 Clouds and convective processes How organised is extreme rainfall in Australia, as seen from satellite observations? White, Bethan1, Jakob, Christian1, Reeder, Michael1

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia

Session 2.3 – February 5, 2018, 1445-1500

Convection is observed to organise across a wide range of scales in both the tropics and midlatitudes, from the few kilometres and hours associated with individual cloud systems, through the mesoscale of squall lines and cloud clusters, to the synoptic scale of tropical cyclones. Additionally, the diurnal cycle of convection has an important role in the triggering and control of these systems. However, the processes responsible for convective organisation, and the interactions between spatiotemporal scales of convection, are still poorly understood, and global and limited area models often fail to represent organised convection.

In this work, we investigate how the character of rainfall extremes in Australia couples to the tropical multi-scale dynamical systems the convection is embedded within. We focus on 800 x 800 km2 regions centred on major Australian cities in different meteorological regimes, from the tropics though the sub-tropics and mid-latitudes. We apply a new convective organisation metric (White et al., 2017) to long-term high-resolution (8km, 30-minute) satellite observations of precipitation, allowing us to identify relationships between extreme rainfall in Australia and the degree of organisation of the rain and associated convection. The metric quantifies the degree of organisation between objects in a binary field. By using different thresholds for the definition of “extreme” rain used to derive this binary field, we systematically explore how the nature of rainfall organisation depends on the definition of extreme rain.

Our results identify key relationships between the structure of the rainfall distributions in each regional location with the distribution of convective organisation. These results are important not only for better understanding the physical processes underlying the nature of rainfall extremes across Australia, but also provide information as to how organised rainfall could be better represented in model parameterisations.

108

The universal scaling characteristics of tropical oceanic rain clusters Cheung, Kevin1, Teo, C.-K.2, Nuynh, H.-N.3,4,5, Koh, T.-Y.2, Legras, B.6, Chew, L.-Y.3, Norford, L.7,8

Presenting author’s e-mail: [email protected]

1Macquarie University, NSW, Australia 2Singapore University of Social Sciences, Singapore 3Nanyang Technological University, Singapore 4Institute of High Performance Computing, Singapore 5Imperial College London, U.K. 6Laboratoire de Météorologie Dynamique CNRS and Ecole Normale Supérieure, France 7CENSAM, Singapore-MIT Alliance for Research and Technology, Singapore 8Massachusetts Institute of Technology, U.S.A.

Session 2.3 – February 5, 2018, 1500-1515

Using multiyear satellite rainfall estimates, the distributions of the area, and the total rain rate of rain clusters over the equatorial Indian, Pacific, and Atlantic Oceans was found to exhibit a power law f(s) ~ sζ, in which s represents either the cluster area or the cluster total rain rate and f(s) denotes the probability density function of finding an event of size s. The scaling exponents ζ were estimated to be 1.66 ± 0.06 and 1.48 ± 0.13 for the cluster area and cluster total rain rate, respectively. The two exponents were further found to be related via the expected total rain rate given a cluster area. These results suggest that convection over the tropical oceans is organized into rain clusters with universal scaling properties. They are also related through a simple scaling relation consistent with classical self- organized critical phenomena. The results from this study suggest that mesoscale rain clusters tend to grow by increasing in size and intensity, while larger clusters tend to grow by self-organizing without intensification.

109

Convective-environment interaction explored by linear response matrix Song, Siwon1, Mapes, Brian2

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2University of Miami, Florida, USA

Session 2.3 – February 5, 2018, 1515-1530

Significant modes of convection-environment interaction are explored by linear response matrices, which link inputs (thermodynamic profiles of temperature and humidity) and outputs (convective tendencies). Linear response matrices are constructed by calculating convective tendency responses to small perturbation forcing at every vertical level with Cloud Resolving Model (CRM) simulations (Kuang 2010, 2012), and one of them in a 128-km square domain (hereafter “M”) is examined in the eigen space. It reveals well-known major deep convective and stratiform modes of Mesoscale Convective Systems (MCSs). Therefore, linearity as an idealized concept appears sufficient to capture the major characteristics of MCSs, and it could be helpful in understanding their interactions with the environment through a simple linear decomposition method. Using the linearity, matrices are modified by adding or subtracting interesting modes of deep convective, stratiform, and no mid-level humidity modes (hereafter, “modified M”), and applied to prognose the behavior of convection in a simple dry General Circulation Model (GCM). Some early results shows that differently modified Ms showed clear distinction of convective feedbacks as tropical convective waves are damped or enhanced corresponding to each mode. However, results are not only opposite than our expectation, but also exhibited a few unrealistic responses. This is a beginning stage to attempt applying easily interpretable linearity to the nonlinear convective behaviors in the interactive framework. Although there are inconsistent behaviors of convection between analyses of individual convective modes and their application in the global model, some rational diagnoses are available through the comparison between experiments, whether or not results are expected or unexpected. Therefore, using the linear relationship by elegantly calculated M would be a challenge, but really a promising way to provide some insight for interactive mechanism between convection and its environment.

110

Implementing the stochastic multi cloud model (SMCM) into the ICON global climate model Moebis, Benjamin1, Jakob, Christian1, Peters, Karsten2, Raut, Bhupendra1, Protat, Alain3

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia 2Max Planck Institute for Meteorology, Hamburg, Germany 3Australian Bureau of Meteorology, VIC, Australia

Session 2.3 – February 5, 2018, 1645-1700

Most cumulus parameterizations used in weather and climate models are built on the assumption that there is a unique small scale response to each possible large scale state. Nevertheless, observations show a significant variability in cumulus activity for a given large scale state, especially as the model grid-size reduces. This variability can be parameterized using Markov chains conditioned on the large- scale state to predict convective area fractions at cloud base.

One such parameterizations is the Stochastic Multi Cloud Model (SMCM). Here we report on the implementation of the SMCM in the Max Planck Institute for Meteorology ICON global climate model. In this implementation mid-tropospheric humidity and vertical velocity are used to predict the fraction of the grid-box covered by congestus clouds as well as deep convection. A comparison with radar observations from Darwin northern Australia shows considerable skill of the statistical model in reproducing the observed behavior of both the mean and the variability of deep and congestus convective area fraction. Together with assumptions on density and vertical velocity at cloud base the predicted area fractions are used as a cloudbase massflux closure in the mass-flux based convection parametrization in ICON. We further modify the convection parametrization to allow simultaneous multiple updrafts of shallow, congestus, deep and mid-level convection.

Results show a significant improvement in the simulation of tropical variability without a deterioration of the model mean state. These changes are associated with changes in the variability of precipitation. We will provide insight into which changes to the parametrization may have caused the positive responses in rainfall and wave activity in the tropics.

111

Radiative-Convective Equilibrium and organized convection – An observational perspective Jakob, Christian1,2,3, Jungandreas, Leonore4, Singh, Martin1

Presenting author’s e-mail: [email protected]

1School of Earth Atmosphere, and Environment, Monash University 2ARC Centre of Excellence for Climate System Science, Monash University 3ARC Centre of Excellence for Climate Extremes, Monash University 4Universität Leipzig, Leipzig, Germany

Session 2.3 – February 5, 2018, 1700-1715

Globally averaged the atmosphere is in Radiative-Convective Equilibrium (RCE) where its net radiative cooling is balanced by condensation heating and therefore, to first order, precipitation. The simplicity of this concept has tempted many to assume its validity on smaller and smaller scales down to a few hundred kilometres. In particular, simulations with cloud models are often carried out in RCE even with very small domains to discover physical mechanisms acting in tropical convection.

Using a variety of satellite observations, from CERES radiative fluxes to ISCCP cloud regimes, we investigate the scales at which RCE is likely a useful assumption. In particular, we link the existence/absence of RCE to the presence/absence of deep convective systems and their state of organization by combing a new data product that measure the “distance from RCE” for a given domain with cloud regime information that allows us to identify regions of organized convection.

We demonstrate that on scales smaller than several thousand kilometres, the atmosphere is in Radiative Convective Anti-Equilibrium, i.e., the more it rains the less the atmosphere cools radiatively. At larger scales, RCE conditions are accompanied by an “optimal” mixture of regions of organized convection and suppressed conditions. The size of the suppressed area needs to be O(10) times larger than the convective area to achieve RCE.

Our findings demonstrate the fundamental importance of dynamical processes in achieving RCE and throw doubt on the use of the assumption of RCE on small scales.

112

The impacts of lower stratospheric stability changes on deep convective transport Mullendore, Gretchen1

Presenting author’s e-mail: [email protected]

1University of North Dakota, North Dakota, USA

Session 2.3 – February 5, 2018, 1715-1730

Deep convection plays an important role in the global circulation. In particular, deep convection mixes mass and momentum vertically. Averaged over large temporal and spatial scales, the tropopause is the upper limit of this vertical mixing. Much like an inversion above the atmospheric boundary layer, the strong increase in potential temperature at the tropopause level caps deep convection. However, at convective scales, the tropopause is much more complicated; it is well known that convection can inject mass directly into the lower stratosphere. Additionally, recent studies suggest that variations in lower stratospheric stability structures lead to different amounts of convective mass transport, but little is known about how variable temperature structures at and around the altitude of the tropopause impact this transport. This study presents a detailed investigation of the mechanisms of vertical mixing at storm top and the impacts of varied stability structures on these mixing pathways. Best practices for defining the tropopause in convective studies is also discussed, with recommendations on how to refine the methods of communicating tropopause properties in the deep convective community.

113

A thermodynamic constraint on the depth of the global tropospheric circulation Thompson, David W. J.1, Bony, Sandrine2, Li, Ying1

Presenting author’s e-mail: [email protected]

1Department of Atmospheric Science, CSU, Fort Collins, CO USA 2Sorbonne Université, LMD/IPSL, CNRS, Univ Paris 06, 75252 Paris, France.

Session 2.3 – February 5, 2018, 1730-1745

The tropopause denotes the discrete boundary between levels of the atmosphere marked by a) vigorous diabatic mixing and low static stability, and b) relatively weak diabatic mixing and high static stability. A discrete boundary between levels of vigorous and weak diabatic mixing can arise from a range of radiative and dynamical processes. Here we will propose that the discrete tropopause arises in large part from the rapid decrease in saturation water vapor and thus radiative cooling by water vapor in the upper troposphere. I will present evidence that suggests the same basic thermodynamical properties that govern the temperature of tropical anvil clouds strongly constrain the depth of the troposphere, the temperature of high clouds, and the amplitude of large-scale dynamics throughout the globe. The results suggest that the positive climate feedbacks associated with high clouds at tropical latitudes also operate at extratropical latitudes.

114

2.4 Australia-Asian monsoon and their interactions in current and future climate A comparison of onset definitions for the North Australian Monsoon Lisonbee, Joel1,2, Ribbe, Joachim1

Presenting author’s e-mail: [email protected]

1University of Southern Queensland, Qld, Australia 2Bureau of Meteorology, ACT, Australia

Session 2.4 – February 6, 2018, 0930-0945

The North Australian Monsoon (NAM) has significant impact on hundreds of thousands of people across northern Australia. The rainfall, winds, and potential for tropical cyclone genesis during an active monsoon phase affects transportation, defence, tourism, public safety, agriculture, fire regimes and energy production, just to name a few. The annual monsoon pattern includes an onset, or the much anticipated first active monsoon period of the season.

In this presentation, we review NAM onset definitions and compare and contrast them with each other. The NAM onset has been defined and measured in at least 12 different ways since the first paper on the subject by Troup in 1961. Most NAM onset criteria are based on either rainfall across Australia's Top End or a reversal of wind at Darwin. A few definitions include both winds and rain in the onset requirements, and some attempt to derive indices from the broad scale circulation in the region. A comparison of these different NAM onset definitions shows similar behaviour in the monsoon seasonality regardless of the defined criteria, with differences in the finer detail. For example all definitions place the mean onset date within the same time of the year, but the exact mean can vary from early December to early January.

115

Trends, variability and extremes of maritime continent rainfall: a weather regimes perspective Hassim, Muhammad1, Timbal, Bertrand1

Presenting author’s e-mail: [email protected]

1Centre for Climate Research Singapore, Meteorological Service Singapore, Singapore

Session 2.4 – February 6, 2018, 0945-1000

Situated within the larger Australian-Asian monsoon region, the Maritime Continent experiences substantial rainfall variations on multiple timescales from diurnal to interannual and longer. In this study, we examine the trends and variability of seasonal and annual rainfall totals over the Maritime Continent from the perspective of objectively-identified weather regimes. A total of eight quasi-static weather regimes are derived using k-means clustering of ERA-Interim reanalysis data for the period December 1980 to November 2014. The technique involves vertical profiles of reanalysis zonal and meridional winds, temperature and specific humidity extracted over Singapore (i.e., ‘soundings’).

Composites of the associated large-scale synoptic flow and rainfall patterns suggest that the recurring large-scale weather regimes correspond to the seasonal march of the Inter-Tropical Convergence Zone (ITCZ) across the northern and southern hemispheres. The regimes are able to depict seasonal variability within the Maritime Continent by capturing the alternating dry and wet phases of the prevailing monsoon. We describe the different degrees of variability within each regime and consider the modulating influence of known climate modes, such as the El-Nino Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation. Warm, cold and neutral phases of ENSO are found to impact each regime differently, most prominently on occurrence frequencies. We also decompose the annual rainfall trend into contributions related to (1) changes in the relative frequency of regime occurrence and (2) changes in within-regime precipitation, following the method of a previous study for Darwin. Lastly, we attempt to identify the regime dependence of extreme (≥ 95th percentile) daily rainfall totals, thereby showcasing the potential utility of weather regimes in isolating broad meteorological situations that are more conducive to precipitation extremes.

116

The dynamics of Australian monsoon bursts in coupled climate models Narsey, Sugata1, Reeder, Michael1, Ackerley, Duncan2, Jakob, Christian1

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia 2Met Office, Exeter, United Kingdom

Session 2.4 – February 6, 2018, 1000-1015

The realism of coupled climate model simulations of the Australian monsoon has been found to be variable, and climate change projections in the region are highly uncertain. It is difficult to comprehensively evaluate the Australian monsoon across many climate models as the monsoon is highly variable both temporally and spatially. The present study aims to clarify the dynamics of sharp intra-seasonal transitions during the Australian monsoon in coupled climate models.

The Australian monsoon occurs as a series of active periods of heavy rainfall known as bursts, interspersed with relatively dry periods referred to here as breaks. We investigate the initiation of bursts, characterising each event by the dynamical processes responsible for the observed circulation tendencies in the Australian monsoon region.

In reanalyses, the initiation of approximately two thirds of all Australian monsoon bursts is found to be most strongly related to the passage of a mid-latitude trough. The remaining third have a stronger tropical signature associated with the Madden-Julian Oscillation (MJO). We evaluate these features in 29 coupled climate models from the CMIP5 archive. Overall there is remarkable agreement between models on the mid-latitude influence on Australian monsoon bursts, with most models showing a mid- latitude wave pattern prior to a composite monsoon burst. However, too many of the simulated bursts are not related to the passage of a mid-latitude trough, and the composite of these events does not resemble the MJO-like pattern found in reanalyses.

The simulation of Australian monsoon bursts under several climate change scenarios is also investigated. We calculate the changes in the numbers of bursts and identify how the dynamics influence the initiation of bursts in coupled climate models. These projections of Australian monsoon bursts are discussed in the context of other projection studies of the Australian monsoon region.

117

GCM precipitation biases in Australian monsoon and maritime continent linked to temporal and spatial intermittency of sub-daily precipitation Moise, Aurel F.1, Martin, Gill M.2, Klingamann, Nicholas P.3

1Bureau of Meteorology, Melbourne, Australia 2Met Office, Exeter, UK 3National Centre for Atmospheric Science-Climate and Department of Meteorology, University of Reading, UK

Session 2.4 – February 6, 2018, 1015-1030

The realistic representation of tropical rainfall both in time and space has been a longstanding challenge for global climate models. Despite some improvement seen over recent years, large biases across tropical regions remain, especially across the Maritime Continent and Australian Monsoon domain. Previous studies have highlighted that climate model biases on multi-year and global scales both develop within a few days of the start of the simulation and are closely related to deficiencies in the simulation of processes on much shorter and smaller scales. Different model parameterizations can produce either very intermittent or very persistent rainfall at the level of the model’s time-step and grid scale, and also produce a poor representation of the processes and timing associated with the diurnal cycle of convection over land. Such deficiencies can have a significant impact on the regional-scale circulation and water cycle and thereby undermine confidence in projections of the spatial and temporal characteristics of heavy rainfall in a future climate. In this study, we examine the distribution of rainfall intensity, and its coherence across temporal and spatial scales, over the Maritime Continent domain and the tropical Australia monsoon region in a subset of recent- generation coupled atmosphere-ocean global climate models. We use a recently-published set of diagnostic tools (ASoP) which allows sub-daily rainfall data from the models to be compared with those from satellite observations (CMORPH and TRMM), and provides insight into how the rainfall variability changes as the temporal and spatial scales increase. The results illustrate contrasting behaviour between the north-westerly and easterly flow regimes of the NW and NE Australia land regions and the topographically-driven rainfall over Papua New Guinea. There is a wide variety of representation of rainfall variability between the models, and the study provides insight into some of the drivers of climatological rainfall biases in the region.

118

Monsoons and tropical rainfall in models and observations Martin, Gill1, Levine, Richard1, Moise, Aurel2, Milton, Sean1

Presenting author’s e-mail: [email protected]

1Met Office, Exeter, UK 2Bureau of Meteorology, Melbourne, Australia

Session 2.4 – February 6, 2018, 1100-1115

Despite considerable efforts worldwide to improve model simulations of monsoon systems, significant biases still remain in climatological seasonal mean rainfall distribution and circulation strength, timing of onset, and inter-annual and intra-seasonal variations. Generally, models often fail to reproduce the observed spatial and temporal distributions of tropical precipitation. The need for improved understanding of how a warming climate may change precipitation variability and extremes has focused model developers' attention on the inability of convection parameterizations to represent the observed range of deep convective processes. Under particular scrutiny are the consequences of poorly simulated sub-daily, grid-point precipitation variability on rainfall distributions at longer (e.g., daily, seasonal, decadal) timescales and larger spatial scales.

The Met Office benefits from a unified modelling strategy where essentially the same modelling system is used across timescales ranging from days to centuries. This allows errors in the monsoon simulation to be examined as they develop, and the relationship between problems with short- timescale variability and longer-term systematic biases to be established. Various areas of study are being pursued at the Met Office, in conjunction with our many collaborators in the UK and worldwide. These include analysis of Asian and Australian monsoons in observations and in simulations with various global configurations and resolutions of the MetUM and various other CMIP5 models, the representation of synoptic-scale systems such as monsoon depressions, and the temporal and spatial intermittency of sub-daily precipitation. Examples of some of this research are given in this talk.

119

East Asian monsoon forecast skill in ACCESS-S1 and sensitivity to land-surface initial conditions Dong, Guangtao1, Zhao, Mei2, Zhang, Huqiang2, Liang, Ping1, Ye, Chengzhi3

1Shanghai Regional Climate Center, China Meteorological Administration, Shanghai, China 2Bureau of Meteorology, Melbourne, Australia 3Hunan Provincial Meteorological Service, China Meteorological Administration, Hunan, China

Session 2.4 – February 6, 2018, 1115-1130

During the development of the Australian Bureau of Meteorology's next generation seasonal forecast system (ACCESS-S1), a series of experiments were conducted to assess the model forecast sensitivity to its land-surface initial conditions (Zhao M., H. Zhang, I. Dharssi, 2017 : Impact of land-surface initialization on ACCESS-S1 and comparison with POAMA. Bureau of Meteorology Research Report No.23 2017). When the system was initialised with observation-driven rather than climatological soil moisture initial conditions, there was a significant improvement in the seasonal and intraseasonal forecast skill over Australia in May-Jun-Jul for surface maximum temperature (Tmax) and latent heat flux, with moderate improvements in surface minimum temperature (Tmin) and precipitation, particularly over the north-eastern part of the continent. Previous studies have suggested an important role of pre-monsoon soil moisture for monsoon onset, rainfall location and intensity in the Asian monsoon region. In this collaborative study we explore such impacts in the same ACCESS-S1 experiments as used in Zhao et al. (2017) for the hindcast period of 1990-2012, focusing on the forecasts with start time of 1st May. This serves as part of the research to better understand land-air interactions in ACCESS-S. In addition, the model forecast skill of atmospheric moisture transport from the tropical warm oceans into the Asia and Australian continents will also be assessed by "atmospheric river" analysis through a collaborative project between the Bureau of Meteorology and China Meteorological Administration.

120

Rossby wave theory in a horizontally nonuniform basic flowand Asian-Australian monsoon interaction Li, Jianping1,2, Li, Yanjie3, Zhao, Sen3,4

1State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing, China 2Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China 3School of Ocean and Earth Science and Technology, University of Hawaii at Mānoa, Honolulu, HI, USA 4Key Laboratory of Meteorological Disaster of Ministry of Education, and College of Atmospheric Science, Nanjing University of Information Science and Technology, Nanjing, China

Session 2.4 – February 6, 2018, 1130-1145

A two-dimensional spherical Rossby wave theory in a horizontally nonuniform basic flow is introduced to study interhemispheric teleconnections, especially Asian-Australian monsoon interaction. The wave theory shows that the meridional group velocity of Rossby waves in horizontally nonuniform background flow has the same direction as the meridional basic wind at the traditional critical latitude, and the stationary waves with a specific wavelength can propagate across the easterlies from south (north) to north (south) via southerly (northerly) flows. Hence, energy transport by stationary waves on a horizontally nonuniform basic state may produce interhemispheric responses that could pass through the tropical easterly belt.In boreal winter and summer, cross-equatorial flows steer stationary waves propagating from one hemisphere to the other across the tropical easterlies, especially over the Australian–Asian monsoon region. It seems that thelarge-scale monsoonal background flows play a critical rolein interhemispheric teleconnections. The wave theory is applied to investigate some interesting interhemisphericteleconnections, for instance, the North Africa–Antarctic (NAA) pattern, North Pacific–South America (NPSA) pattern, and Southern Africa–South Asia–North Pacific (AAP) pattern, which are not supported by the traditional Rossby wave theory, since stationary waves in a basic state without meridional wind would be trapped in the easterlies. In fact, the wave theory can be also used to study various teleconnection patterns on various time scales. We here take some decadal and multidecadal teleconnection patterns such as the EurAsian multidecadal teleconnection pattern (EAMT), Africa–Asia multidecadal teleconnection pattern (AAMT), decadal-scale South Atlantic–Australia (SAA)teleconnection, etc. as examples. The wave ray trajectory and model results suggest that these patterns may result from Rossby wave energy dispersionin horizontally nonuniform background flow.

121

Diagnosing remote and locally forced systematic errors in monsoon simulations Milton, Sean1, Rodriguez, Jose1, Sanchez, Claudio1, Maria, Carvalho1, David Sexton1, Martin, Gill1

Presenting author’s e-mail: [email protected]

1Met Office, Exeter, UK

Session 2.4 – February 6, 2018, 1145-1200

The simulation of global monsoon systems remains a significant challenge for many modelling centres both at weather and climate timescales (e.g. Sperber et. al., 2012). The Met Office Unified Model is a seamless prediction system used across a range of prediction timescales from short-range NWP, seasonal and decadal prediction and climate projections. The representation of global monsoons in the Unified Model remains a significant source of model error and projection uncertainty.

In this talk we explore the use of a variety of complementary diagnostic techniques applied to the problem of understanding sources of model systematic error in monsoon simulations. These include (i) a nudging/relaxation technique to explore remote forcing/teleconnections on monsoon circulations, (ii) the use of initial tendencies from short-range NWP simulations, including a PV tracer technique, to explore the local interactions between parametrised heating/momentum forcing and monsoon circulations, (iii) studies of the role of model resolution and coupled atmosphere-ocean-land interactions at weather and climate timescales, and (iv) use of a perturbed parameter ensemble (PPE) to explore the role of parametrization uncertainties.

Reference: Sperber, K. R., Annamalai, H., Kang, I. S., Kitoh, A., Moise, A., Turner, A., et al. (2012). The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century. Climate Dynamics, 41(9-10), 2711–2744. http://doi.org/10.1007/s00382-012-1607-6

122

Inter‑decadal changes in the East Asian summer monsoon and associations with sea surface temperature anomaly in the South Indian Ocean Zhiping, Wen1, Haiyan, Zhang1, Renguang, Wu2

Presenting author’s e-mail: [email protected]

1Sun Yat-sen university, Guangzhou, China 2Institute of Atmospheric Physics, CAS, Beijing, China

Session 2.4 – February 6, 2018, 1200-1215

Previous studies have revealed inter-decadal changes in the East Asian summer monsoon (EASM) that occurred around the late 1970s and early 1990s, respectively. The present study compares characteristics of these two changes and analyzes plausible influences of the South Indian Ocean (SIO) sea surface temperature (SST) change. The two changes share pronounced common features, characterized by an equivalent barotropic circulation anomaly over northern East Asia and a meridional vertical overturning circulation over the tropical region. Meanwhile, they display some distinct characteristics, especially over the tropics. The circumfluent anomalies are more robust for the first change than for the second one. Related amplitude asymmetry is partly attributed to a weakening trend in the EASM. Moreover, SST change in the SIO, featuring a decadal warming since the 1980s and a cooling after 1993, may contribute to both of these inter-decadal changes. Cold SST anomaly induces anomalous mid-tropospheric descent over the western SIO and ascent extending from the eastern SIO to western Australia and over the equatorial Indian Ocean. The accompanying upper-tropospheric divergent flows from western Australia and equatorial Indian Ocean to the Philippines lead to anomalous descent and an anomalous lower-tropospheric anticyclone over the South China Sea–Philippines. Warm SST anomaly induces opposite changes in above regions. The possible influence of SST anomaly in the SIO is further confirmed by numerical experiments.

123

Impacts of the Indian Ocean Dipole on the summer water vapour transport into the South China Sea region Dai, Zejun1, Zhang, Jianqi1, Ye, Chengzhi1, Chen, Jingjing1, Mo, Ruping2

Presenting author’s e-mail: [email protected]

1Hunan Meteorological Service, Changsha, Hunan, China 2Environment and Climate Change Canada, Vancouver, BC, Canada

Session 2.4 – February 6, 2018, 1215-1230

Impacts of the Indian Ocean dipole (IOD) on the southwesterly monsoonal airflow bringing moist air from the tropical Indian Ocean into the South China Sea (SCS) in the boreal summer season are investigated in this study, using data from the NCEP/NCAR Reanalysis and an atmospheric general circulation model (GCM) simulation. Our results indicate that water vapour transport through the southwest flow into SCS is stronger when the IOD is in the positive phase when the sea surface temperatures (SSTs) are warmer in the western tropical Indian Ocean and cooler off the Sumatra. This pattern of anomalous SSTs affects the eastward propagation of the Madden-Julian Oscillation (MJO) along the equator and strengthens its meridional propagation off the equator, leading to stronger convective activities with deep cumulus clouds over the Bay of Bengal. A secondary circulation driven by the latent heat of convection enhances the subtropical high in the western Pacific and forces it to locate at higher latitudes. This situation is beneficial to the establishment and strengthening of the moisture transport through the southwesterly monsoonal flow into the SCS. In addition, stronger convective activities over the Bay of Bengal and the Indochinese Peninsula with cooler SSTs off the Sumatra lead to a stronger reverse-Hadley circulation with a strong cross-equatorial southerly flow to reinforce the moisture transport into the SCS. During the negative phase of IOD, the MJO signal is stronger over the eastern tropical Indian Ocean, and its eastward propagation strengthens the easterly flow on the southern blank of the subtropical high in western Pacific, which in turn acts to suppress the moisture transport by the southwest monsoon into the SCS.

124

Australian-Asian monsoon under BoM-CMA collaborative research: progress and prospects Zhang, Huqiang1, Moise, Aurel1, Ye, Chengzhi2, Dong, Guangtao3, Liang, Ping3, Xu, Ying4

Presenting author’s e-mail: [email protected]

1Australian Bureau of Meteorology, VIC 3001, Australia 2Hunan Provincial Meteorological Service, China Meteorological Administration, Hunan, China 3Shanghai Regional Climate Center, China Meteorological Administration, Shanghai, China 4National Climate Center, China Meteorological Administration, Beijing, China

Session 2.4 – February 6, 2018, 1430-1445

The Australian-Asian (A-A) monsoon plays a key role in governing the weather and climate in the Australia-Asian region, yet it remains a challenge to skilfully predict its variations in current and future climate which operate across a range of temporal and spatial scales. In the last decade or so, there have been a series of collaborative research projects in this area under the bilateral cooperation agreement between Australian Bureau of Meteorology (BoM) and China Meteorological Administration (CMA). In this presentation, we will highlight some achievements in studying the A-A monsoon including: (i) the monsoon interactions at monthly and seasonal time scales in which we showed the impacts of Asian winter monsoon on the tropical Australia climate through enhanced cross-equatorial flows; (ii) the diagnosis of monsoon onset/retreat in current and future climate using large-scale wind and moisture indices; and (iii) the results from a series of ACCESS numerical experiments exploring uncertainty in our projection of potential changes in the A-A monsoon in warmed climate. Some current and future activities will also be discussed, including the diagnosis of tropical-extratropical interactions and atmospheric river analysis in the region, and monsoon prediction at intra-seasonal and seasonal time scales over the Australian and Asian region. We demonstrate the great benefits of such collaborations which lead to better understanding of the weather and climate in the region.

125

Characteristics of water vapour transport and atmospheric river analysis in Asian-Australian Region: A CMA-BoM bilateral project Ye, Chengzhi1, Zhang, Huqiang2, Moise, Aurel2, He, Weiwei3, Chen, Deqiao3

Presenting author’s e-mail: [email protected]

1Hunan Meteorological Service, Changsha, Hunan, China 2Bureau of Meteorology, Melbourne, Victoria, Australia 3Meteorological Observatory of Hengyang City, Hunan, China

Session 2.4 – February 6, 2018, 1445-1500

Under a cooperation agreement between China Meteorological Administration (CMA) and the Australian Bureau of Meteorology (BoM), we have established a bilateral project to study the characteristics of atmospheric water vapour transport in the Australia-Asian monsoon region using “atmospheric river (AR)” diagnosis. AR refers to long and narrow bands of enhanced water vapour transport in the lower troposphere, often forming over warm oceans with the potential of producing heavy precipitation over the land. Studies have shown they are instructive in studying extreme rainfall events, but limited research has been conducted in the Australia-Asian region. In this presentation, we will give an overview of the project, highlight some preliminary results so far and discuss future activities.

Using the JRA 55-year reanalysis, the CPC Merged Analysis of Precipitation, and some other circulation indices and climate data, we show that a strong East Asian monsoon is accompanied by a weaker subtropical high in the western Pacific and a stronger low pressure trough over the Bay of Bengal. The weaker subtropical high is located further to the north and to the east as compared with its normal position. The associated Mei-Yu front is also weaker. A deeper trough over the Bay of Bengal leads to stronger moisture transport from the South Asia into the South China Sea, and the onshore flows carry moist air to northern China. By comparison, a strong Australian summer monsoon is accompanied by a deeper monsoon trough over northern Australia and a stronger Mascarene high in the southern Indian Ocean. This anomalous circulation pattern leads to strong moisture transport into northern and eastern Australia, resulting in heavier rainfall in these areas. Detailed AR analysis will reveal some different characteristics of atmospheric moisture transport in the Asian and Australian monsoon regions. Particular attention will also be paid to explore how the Indian Ocean moisture is transported into the Australian continent during different IOD phases and the linkage between AR and the Northwest Cloud Band (NWCB) affecting rainfall in the Australian region. Finally, we also investigate the combined impacts of weakened monsoon circulations but enhanced moisture source from warmed tropical oceans under global warming on the ARs in the Australian-Asian monsoon region and how that affects its rainfall variations.

126

Continental atmospheric rivers over China and Australia: two case studies Chen, Jingjing1, Ye, Chengzhi1, Zhang, Huqiang2, Moise, Aurel2, Mo, Ruping3

Presenting author’s e-mail: [email protected]

1Hunan Meteorological Service, Changsha, Hunan, China 2Bureau of Meteorology, Melbourne, Australia 3Environment and Climate Change Canada, Vancouver, BC, Canada

Session 2.4 – February 6, 2018, 1500-1515

Atmospheric rivers (ARs) are long and narrow bands of enhanced water vapour transport in the lower troposphere, often forming over the oceans with the potential of producing heavy precipitation during their landfalls. In this CMA-BoM collaborative study, we compare detailed structures and evolutions of two ARs events: one over East Asia and the other one over the Australian continent. An AR was developed over China during 17-21 July 2016. It was initiated by a Lee low forming to the east of the Taihang Mountains. A low level jet associated with the quasi-stationary low pressure system brought warm, moist air from the South China Sea and southern China to the North China Plain. It eventually transformed into a powerful AR which can be clearly identified on the charts of integrated water vapour transport (IVT). Strong moisture convergence occurred along a cold front and near the mountains where the AR was blocked. The combined effect of the warm and moist air and orographic uplift associated with the mountain slopes caused torrential rains in North China. The other continental AR event analysed in this study occurred over Australia during 27-31 August 2016. It began with an developed over the southern Indian Ocean region southwest of the Australia. This low pressure system, interacting with systems in the tropics, was capable of pumping up moist air from the tropical Indian Ocean to form a trans-Australia AR, as evident from the animation of a series of IVT maps. This AR event produced an impressive rain belt across Australia, although the rainfall amounts were not excessively high. Moisture backward trajectory analysis has been used to identify the moisture sources for these events. We also further contrast some detailed features of these two ARs and their associated rainfall generations.

127

An analysis of atmospheric rivers embedded in the monsoonal flows and associated heavy rainfall events over China and Australia Xu, Lin1, Fu, Chenghao1, Chen, Hongzhuan1, Mo, Ruping2

Presenting author’s e-mail: [email protected]

1Hunan Meteorological Service, Changsha, Hunan, China 2Environment and Climate Change Canada, Vancouver, BC, Canada

Session 2.4 – February 6, 2018, 1515-1530

During 17-21 June 2016, heavy rainfall occurred in the Yangtze-Huai River Basin of China and in some areas of Australia. The moisture origins and the moisture transport leading to these heavy precipitation events are analyzed in this study. It is shown that some of these heavy precipitation events can be attributed to atmospheric rivers (ARs), which appeared as narrow corridors of strong water vapor transport embedded in the monsoonal airflows. In the first stage of this period, moisture in the tropical Pacific Ocean was transported into the South China Sea and was then carried by onshore flow to feed an AR over eastern China. This inland AR produced a long band of heavy precipitation along the Yangtze River Basin. Moisture in the tropical Pacific also flowed southward to form an AR on the East Coast of Australia, leading to heavy precipitation in Queensland and New South Wales during 18-19 June. In the second stage starting from 20 June, the Indian monsoon system split into two moist branches, with one entering South China Sea and then flowing onshore to support the inland AR over eastern China, and the other travelling southward to form an AR across Australia. The AR over China produced heavy precipitation in Anhui Province on the 20th and in Jiangsu Province on the 21st of June. The trans-Australia AR only triggered some moderate precipitation events in western and eastern Australia. It is demonstrated that high water vapor content and strong moisture convergence are critical for the heavy rainfall generation over the complex terrain of eastern China. Our study indicates that the conceptual model of AR has the potential to improve our scientific understanding and operational prediction of heavy precipitation events in the Australian-Asian monsoon region.

128

Tempo-spatial distributions and variations of atmospheric rivers affecting Australia and East Asia Wu, Xianyun1, Chen, Jingjing2, Xu, Lin2, Ye, Chengzhi2, Mo, Ruping3

Presenting author’s e-mail: [email protected]

1Hunan Climate Center, Changsha, Hunan, China 2Hunan Meteorological Service, Changsha, Hunan, China 3Environment and Climate Change Canada, Vancouver, BC, Canada

Session 2.4 – February 6, 2018, 1530-1545

Atmospheric rivers (ARs) are narrow corridors of enhanced water vapour transport in the troposphere with the potential to trigger extreme precipitation in geographically favourable locations. Based on the Japanese 55-year Reanalysis data, the spatial distributions and temporal variations of ARs affecting Australia and China over the 1977-2016 period are examined and compared in this study. ARs are detected using a criterion of 500 kgm-1s-1 of integrated water vapour transport. Over this 40-year period, there were about 200 ARs in the Australian region accompanied by band-shaped precipitation. These Australian AR events usually lasted for 24 to 120 hours, with the longest ones persisting over 10 days. They occurred most frequently in the 1980s and early 1990s, becoming less frequent in the period 1995-2005, and showing an increasing trend in the recent years. The months with most ARs are May and July, and these ARs mainly affect southern Australia. ARs also frequently occur in October and December and often affect northern and eastern Australia. The moisture sources of the Australian ARs and the connection with Northwest Cloud Band are also analysed in this study. The ARs affecting China often occur in the period between April and September. They usually appear as a southwest-to- northeast moisture corridor across eastern China. There are two major moisture sources for these Chinese ARs: 1) moisture in the Bay of Bengal flowing across the Indochinese Peninsula and then into China; 2) moisture in the tropical Pacific flowing westwards along the southern frank of the subtropical high and making landfall on the Chinese coastline. A strong subtropical high in summer could force an AR penetrating inland into northern China. Comparison of different AR features in the Australian and Asian regions helps us better understanding of the role of moisture transport in extreme rainfall generations in the monsoon region.

129

Atmospheric river analysis: diagnosing heavy precipitation based on the convergence of integrated water vapour flux and a column saturation index Mo, Ruping1, Xu, Lin2, Ye, Chengzhi2

Presenting author’s e-mail: [email protected]

1Environment and Climate Change Canada, Vancouver, BC, Canada 2Hunan Meteorological Service, Changsha, Hunan, P. R. China

Session 2.4 – February 6, 2018, 1645-1700

Atmospheric Rivers (ARs) are long, narrow bands of enhanced water vapour transport in the lower troposphere. They are responsible for most of the poleward moisture transport at mid-latitudes and can produce extreme precipitation events under favourable geographical conditions. A basic AR analysis usually involves examination of the vertically Integrated Water Vapour (IWV) and/or Integrated water Vapour Transport (IVT). However, neither IWV nor IVT can be directly correlated with precipitation. It is the moisture convergence that makes a major contribution to the heavy precipitation in an AR scenario.

In this study, some methods for diagnosing AR-induced heavy precipitation are proposed. It is shown that the precipitation rate is determined primarily by the convergence of IVT, which can be used to define an Equivalent Precipitation Rate (EPR) for a rough estimate of precipitation intensity. Since only a fraction of the converged moisture is condensed out as precipitation (the remaining fraction is stored and acts to increase the humidity of the air column), the accuracy of EPR as a proxy of actual precipitation rate depends crucially on the degree of saturation of the column. A more accurate method for estimating the precipitation rate can be obtained by combining the EPR with a column saturation index, which can be defined as the ratio of IWV and its maximum value calculated from a fully saturated column. An empirical scheme for calculating the so-called “Pseudo-Precipitation Rate” (PPR) is proposed. The usefulness of PPR as an estimate of the actual AR-induced precipitation rate is demonstrated in a case study with data collected from observations and model predictions of the ARs occurring on 7 November 2016 over China and on the west coast of Canada.

130

Sensitivity of future Australian summer monsoon rainfall to emission scenario Brown, Josephine R.1, Colman, Robert1, Moise, Aurel1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 2.4 – February 6, 2018, 1700-1715

Future simulations of Australian summer monsoon rainfall from climate models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) show a multi-model mean projection of little change, but with large uncertainty. Under the high emission Representative Concentration Pathway (RCP8.5) scenario, the model spread includes large increases and decreases. Previous work has found that those models simulating reduced monsoon rainfall tend to have larger biases in sea surface temperatures in the western equatorial Pacific, and are therefore less credible. In the lower emission RCP4.5 scenario, the influence of non-greenhouse gas forcing, including anthropogenic aerosols, becomes more important. The prescribed decline in aerosols over the 21st century produces a rainfall response that differs spatially from the greenhouse gas response, and leads to fewer models simulating large increases in rainfall over northern Australia in this scenario. The changes in mean summer monsoon rainfall under RCP4.5 and RCP8.5 scenarios are compared, and the relative roles of aerosols and greenhouse gas forcing are identified. Changes in the strength of the South Asian and East Asian winter monsoons are also examined, and the role of modified cross-equatorial circulation in altered Australian summer monsoon strength is quantified.

131

Impact of recent deforestation on the climate of South-East Asia Syktus, Jozef1, Salazar, Alvaro2, Thatcher, Marcus3, McAlpine, Clive2

Presenting author’s e-mail: [email protected]

1The University of Queensland, Global Change Institute, QLD, Australia 2The University of Queensland, School of Earth and Environmental Sciences, QLD, Australia 3CSIRO Marine and Atmospheric Research, Vic, Australia

Session 2.4 – February 6, 2018, 1715-1730

Globally, deforestation continues at alarming rates. From 1990–2015, 129 Mha (3.13%, or an annual rate of 0.13%) of the world’s forests were converted to agriculture, biofuels, mining and urban land uses, or lost due to other causes such as fires and drought. Estimates using high resolution satellite data show that 230 Mha of tree cover was lost globally between 2000 and 2012. The most extensive loss was in the humid tropics which experienced a 62% acceleration in net deforestation from the 1990s to the 2000s. Deforestation in the Amazon basin has long been the focus of international concern, with annual rates in the Brazilian Amazon of 0.1–0.7% per annum from 1988–2015. However, Southeast Asia also has experienced high levels of deforestation in recent decades, particularly in Indonesia, Myanmar and Cambodia. From 1990–2010, the humid forests of insular Southeast Asia had one of the highest global rates of deforestation at around 1% per annum. Since 2000, Indonesia has lost over 6 Mha of primary forest. In 2012, the area of annual loss in Indonesia was nearly twice that of Brazil, with nearly all clearance occurring in lowland forests (51%) or peat swamp forests (43%).

Forests play a critical role in the carbon, water and energy cycles which regulate the Earth’s global and regional climate. Forests are well recognised for their potential to mitigate climate change through carbon sequestration. At a regional scale, forest cover also influences land-surface properties, including evapotranspiration, albedo and surface roughness, which affect the magnitude and form of energy transfer to the atmosphere. By altering the fluxes of heat, momentum and moisture exchanges between the land surface and the lower atmosphere, forests affect climate. Deforestation therefore has the potential to influence regional climates far more rapidly than changes in the global carbon cycle.

The aim of this research is to assess how deforestation may affect the regional climates of Southeast Asia through biophysical processes. We use Conformal Cubic Atmospheric Model (CCAM) developed by CSIRO at 25 km resolution over SE Asian domain to simulate impact of deforestation on regional climate. Two land use and land cover scenarios were used. The first land use scenario represented land use and land cover representative of 1980s and the second of 2010s. Four-member ensemble for each land use scenario was competed for period 1980-2010 using ERA-Interim and 3 selected CMIP5 models (ACCESS1.3, MPI-ESM-LR and HadGem2-CC) as the boundary conditions for the simulations. We will show key changes in simulated surface climate and circulation in the region resulting from different level of deforestation.

132

The anthropogenic contribution to Asia–Australia monsoon system changes Ying, Xu1

Presenting author’s e-mail: [email protected]

1National Climate Center, China Meteorological Administration, Beijing 100081, China

Session 2.4 – February 6, 2018, 1730-1745

In recent years, the climate change research community has become highly interested in describing the anthropogenic influence on different climate system and extreme weather events, commonly termed “event attribution.” In present, large ensembles of high-resolution simulations can be generated under factual observed conditions and counterfactual conditions that might have been observed in the absence of human interference; These can be used to estimate the change in probability of the given event due to anthropogenic influence. The Asia–Australia monsoon system, which has an impact on the climate change over Asia and Australia regions and even the world, plays an important role in the global monsoon. In this work, we estimate the year-to-year variability in calculations of the anthropogenic contribution to Asia–Australia monsoon system and investigate the inter-decadal changes and interaction of the East Asian winter monsoon (EAWM) and Australian summer monsoon (AuSM) and their link to onsets of different types of El Niño under anthropogenic and nature factor contribution based on large ensembles of atmospheric model simulations (CAM5.1 global atmosphere/land climate model). On the other hand, our research both quantify the magnitude of year-to-year variability and categorize the degree to which conclusions of attribute able risk are qualitatively affected by exploring extreme temperature and precipitation events for the China and Australia.

133

2.5 Large-scale atmospheric and climate dynamics of the Southern Hemisphere Exploring the tropical drivers of the Antarctic atmosphere Barrett, Bradford1, Henderson, Gina1

Presenting author’s e-mail: [email protected]

1United States Naval Academy, Maryland, USA

Session 2.5 – February 5, 2018, 1100-1115

Intraseasonal tropical variability has important implications for the mid- and high- latitude atmosphere, and in recent studies has been shown to modulate a number of weather processes in the Northern Hemisphere. In such studies, the extratropical atmosphere has tended to associate with tropical convection of the leading mode of intraseasonal variability, the Madden-Julian Oscillation (MJO), with a time lag of approximately seven days. The time lag between the MJO and the Antarctic atmosphere has been found to vary between less than seven and greater than 20 days. This study builds on previous work by further examining the time-lagged response of Southern Hemisphere tropospheric circulation to tropical MJO forcing, with specific focus on the latitude belt associated with the Antarctic Oscillation, during the months of June (Austral winter) and December (Austral summer) using NCEP-DOE Reanalysis 2 data for the years 1970-2016. The primary findings are: (1) that the time lag with strongest height anomalies depends on both the location of the MJO convection (e.g., the MJO phase) and the season, and (2) that the lagged height anomalies in the Antarctic atmosphere are fairly consistent across different vertical levels and latitudinal bands. In addition, certain MJO phases in December displayed lagged height anomalies indicative of blocking-type atmospheric patterns, with an approximate wavenumber of 4, whereas in June most phases were associated with more progressive height anomaly centers resembling a wavenumber-3 type pattern.

134

Split Jet variability in the South Pacific Winter Patterson, Matt1, Woollings, Tim1

Presenting author’s e-mail: [email protected]

1Subdepartment of Atmospheric Oceanic and Planetary Physics, University of Oxford, Oxford, United Kingdom

Session 2.5 – February 5, 2018, 1115-1130

The winter southern hemisphere lower and upper tropospheric zonal wind fields are both zonally asymmetric. In the lower troposphere there is a contrast between strong winds over the Indian Ocean and more variable winds in the South Pacific region, while at upper levels the wind field is dominated by a strong subtropical jet stretching from the west of Australia into the Pacific. This is in contrast to the Summer, where the absence of a strong subtropical jet leads to a more symmetric wind field.

The winter South Pacific also sometimes exhibits a ‘split’ jet stream, one branch being found in the subtropics and the other at middle or polar latitudes, while at other times during this season these branches are merged. Part of the split jet’s separation is explained by the two distinct mechanisms which drive jet streams - angular momentum transport by the Hadley cell and momentum flux convergence from the generation of synoptic-scale eddies in mid-latitudes.

However, a split jet can sometimes be seen in the lower troposphere, even though the Hadley cell only transports momentum to the upper troposphere. A possible cause of this lower level split is related to atmospheric blocking events, where a high-pressure system redirects the flow of air to the north and south of itself.

An observational study is presented examining the causes of variability in winter South Pacific jet streams. We develop indices to represent the variations in the strength of eddy and Hadley cell driving and show how these affect the zonal wind field. We also study the effect of blocking events in the South Pacific on the jet.

135

Understanding the seasonal cycle of tropical precipitation: a convective quasi- equilibrium model Singh, Martin1

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia

Session 2.5 – February 5, 2018, 1130-1145

Monsoon circulations are a source of precipitation for a large fraction of the world's population. However, our understanding of the physical factors determining the strength, latitudinal extent, and seasonal evolution of monsoons remains incomplete. Here, we use an idealised general circulation model to investigate the behaviour of the seasonal cycle of tropical precipitation across a wide range of climates and planetary parameters. The location and timing of seasonal precipitation maxima in the idealised model are found to correspond to regions in which the curvature of the boundary-layer entropy distribution is large. These results are interpreted using a theory of tropical precipitation based on convective quasi-equilibrium, in which large-scale overturning circulations are predicted to exist whenever the boundary-layer entropy curvature exceeds a critical value. By combining this theory with a simple energy balance model that represents atmospheric transport by down-gradient diffusion of moist static energy, we develop a predictive model for tropical precipitation within the quasi-equilibrium framework. This model shown to provide insight into the mechanisms driving changes in the phasing of the seasonal cycle under global warming, and its potential applicability to Earth's monsoons in current and future climates is discussed.

136

Changes in southern hemisphere explosive storms in a warming climate Osbrough, Stacey1,2, Frederiksen, Jorgen1,2

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, VIC, Australia 2Monash University, VIC, Australia

Session 2.5 – February 5, 2018, 1145-1200

Changes in the southern hemisphere circulation have significant impact on the properties of weather systems associated with mid-latitude storms and heavily influence Australian rainfall. One of the primary causes of the Australian Millennium Drought is the reduction in the growth rates of leading storm track modes and a southward deflection of some storms south of the Australian continent. During this period, some of Australia’s driest years on record were undoubtedly intensified by the occurrence of a strong El Nino event in 1997. The drought was finally broken due to a rapid transition to a wet La Nina in 2010 when record rainfalls were observed across south east Australia.

Here, a new data analysis method is employed to extract growth rates and structures of growing and decaying storms, using six hourly observational data, focusing on explosive systems. Changes in the variance of storms in different growth rate bands are determined and principal oscillation pattern (POP) and empirical orthogonal function (EOF) analyses are used to summarise the changing structures. We investigate the properties of rapid storm development in the late 20th and early 21st century and describe the effects of the ENSO cycle on the location and variance of explosive storms in a warming climate.

137

Monsoon depressions in southern Africa: The Angola Low Howard, Emma1

Presenting author’s e-mail: [email protected]

1School of Geography and the Environment, University of Oxford, United Kingdom

Session 2.5 – February 5, 2018, 1200-1215

The Angola Low has been proven to have an important modulating role on tropical and subtropical southern African precipitation. However, the Angola Low is not a well understood feature of southern African climate. The exact mechanism with which it forms and evolves during the summer months - over which it ebbs and wanes frequently - is unknown. The Angola low exhibits a marked transition in December where it shifts from dry to moist convection.

This work aims to characterise the synoptic expression of the Angola Low. We diagnose the mechanism of these systems by considering the relative vorticity budgets of reanalysis datasets and atmospheric models.

We find that the Angola Low is made up of a combination of dry and moist convective systems, which generate its seasonal transition. The dry systems are heat lows, while the moist systems show similarity to monsoon lows and depressions. These moist systems are more important to Southern African precipitation than the heat lows. The unique topography of Southern Africa allows mesoscale atmospheric features to play an important role in setting up the Angola Low.

While not always considered to be a true monsoon, summer circulation in tropical southern Africa shares many aspects with the climates of monsoon regions. Southern Africa provides a valuable case study of conditions required for a monsoon circulation, as it exists on the fringe of the parameter space.

138

Intraseasonal periodicity in the southern hemisphere circulation on synoptic spatial scales Thompson, David W. J.1, Crow, Brian R.1, Barnes, Elizabeth A.1

Presenting author’s e-mail: [email protected]

1Department of Atmospheric Science, CSU, Fort Collins, CO USA

Session 2.5 – February 5, 2018, 1215-1230

Various measures of Southern Hemisphere extratropical storm activity exhibit periodicity on time scales of 20–25 days. The periodicity is readily apparent in hemispheric averages of eddy kinetic energy and precipitation. In this talk, I will explore the signature of the periodicity on synoptic spatial scales.

The ~20-25 day periodicity in Southern Hemisphere storm activity derives from out-of-phase anomalies in wave activity that form in association with extratropical wave packets as they propagate to the east. In the upper troposphere, the out-of-phase anomalies in wave activity form not along the path of extratropical wave packets, but in their wake. The out-of-phase anomalies in wave activity give rise to periodicity not only on hemispheric scales, but also on synoptic scales when the circulation is sampled along an eastward path between ~5 and ~15 m/s. Analyses with a simple model suggest that the projection of the periodicity onto synoptic scales derives from 1) two-way interactions between the heat fluxes and baroclinicity in the lower troposphere and 2) the contrasting eastward speeds of the source of the periodicity in the lower troposphere and wave packets in the upper troposphere.

139

2.6 Atmospheric – general Meteorological controls on atmospheric particulate pollution during hazard reduction burns Di Virgilio, Giovanni1, Hart, Melissa Anne1,2, Jiang, Ningbo3

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, University of New South Wales, Sydney, 2052, Australia 2Australian Research Council Centre of Excellence for Climate System Science, University of New South Wales, Sydney, 2052, Australia 3New South Wales Office of Environment and Heritage, Sydney, 2000, Australia

Session 2.6 – February 8, 2018, 1700-1715

Internationally, wildfires are an escalating problem likely to worsen given projected changes to climate. Hazard reduction burns (HRB) are used to suppress wildfire occurrences, but they generate considerable emissions of atmospheric fine particulate matter, which depending upon prevailing atmospheric conditions, can degrade air quality. Our objectives are to improve understanding of the relationships between meteorological conditions and air quality during HRBs in Australia. We identify the primary meteorological covariates linked to high PM2.5 pollution (particulates <2.5μm diameter) and quantify differences in their behaviours between HRB days when PM2.5 remained low, versus HRB days when PM2.5 was high. Generalised additive mixed models were applied to continuous meteorological and PM2.5 observations for 2011-2016 at four sites across Sydney. The results show that planetary boundary layer height (PBLH) and total cloud cover were the most consistent predictors of elevated PM2.5 during HRBs. During HRB days with low pollution, the PBLH between 00:00 and 07:00h (local time) was 100-200m higher than days with high pollution. The PBLH was similar during 10:00-17:00h for both low and high pollution days, but higher after 18:00h for HRB days with low pollution. Cloud cover, temperature and wind speed reflected the above pattern, e.g. mean temperatures and wind speeds were 2°C cooler and 0.5 m s-1 lower during mornings and evenings of HRB days when air quality was poor. These cooler, more stable morning and evening conditions coincide with nocturnal westerly cold air drainage flows in Sydney, which is associated with reduced mixing height and vertical dispersion, leading to the build-up of PM2.5. These findings indicate that air pollution impacts may be reduced by altering the timing of HRBs by conducting them later in the morning (by a matter of hours). Our findings support location-specific forecasts of the air quality impacts of HRBs in Sydney and similar regions elsewhere.

140

Regime based evaluation of present day GCM cloud simulations using self organizing maps Schuddeboom, Alex1, McDonald, Adrian1, Morgenstern, Olaf2, Harvey, Mike2, Parsons, Simon1

Presenting author’s e-mail: [email protected]

1University of Canterbury, Christchurch, New Zealand 2National Institute of Water and Atmospheric Research, Wellington, New Zealand

Session 2.6 – February 8, 2018, 1715-1730

Modern climate models have long standing issues related to cloud representation over the Southern Ocean. To investigate these issues, cloud regimes from satellite data are compared to model output. The observational data used in this research includes cloud properties from the Moderate Resolution Imaging Spectroradiometer (MODIS) collection 6 and radiative fluxes from CERES SYN1deg Edition 3A. While the model data is sourced from CFMIP Observation Simulator Package (COSP) output of the New Zealand Earth System Model (NZESM).

Cloud top pressure - cloud optical thickness joint histograms, from MODIS, are clustered using a machine learning technique known as self organizing maps (SOMs). This leads to the identification of 12 different clusters, each one corresponding to a representative cloud regime. The relative frequency of occurrence (RFO) of a cluster and the geographic distribution of RFO are calculated, allowing us to connect our regimes directly to specific regional phenomena such as stratocumulus cloud decks west of South America. The cloud radiative effect (CRE) is calculated from the CERES data and linked to each of the regimes, describing the effect a particular regime has on the transmission and reflection of radiation.

The MODIS derived regimes are then applied to the COSP joint histograms allowing for the clustering of the NZESM data. The geographic distribution of RFO and the CRE of the NZESM regimes are then compared to the MODIS regimes, allowing for the identification of differences in representation. For example, the regime associated with high cloud is identified as having large discrepancies in terms of both occurrence rate and radiative effect. We also see that the radiative bias over the Southern Ocean region is also directly tied to a few regimes.

141

Testing a new hypothesis that increasing use of irrigation water is causing global warming Kennedy, Ivan1

Presenting author’s e-mail: [email protected]

1Sydney Institute of Agriculture, University of Sydney, NSW, Australia

Session 2.6 – February 8, 2018, 1730-1745

The 4-6 year El Nino cycles result in a global mean temperature range of about 1 C, with a peak gradient also near 1 C per year. This is regarded as a result of accelerated evaporation of seawater from a warm Pacific Ocean surface, elevating the maritime atmosphere and reducing the outgoing longwave radiation (OLR) to space by up to one-third. By contrast, global warming of only 1 C per century is attributed to of the trend of increasing greenhouse gases (GSG) in the atmosphere; in climate models, water is assigned a secondary though important amplifying role, but solely as a positive feedback from an atmosphere previously heated by other GHGs. However, this conclusion ignores the elevating tropospheric effects of the increasing use of water to grow crops for the human population, particularly in regions with dryer soil and lower humidity. Rates of irrigation worldwide have increased by around 1.5% annually between 1960 and 2000, declining somewhat since. Importantly, the evaporation of this additional water is dynamically focussed on a small proportion of the Earth's surface, intensifying its potential to elevate the troposphere and reduce the regional OLR, in contrast to the well-mixed tropospheric carbon dioxide. An analysis using the virial theorem to establish temperature gradients suggests that this extra water could locally elevate the atmosphere on a daily basis, reducing the regional OLR sufficiently to steadily warm the Earth, although at a rate only 1-2% that of the El Nino-La Nina cycle. Fortunately, this hypothesis can be tested, using, for example, the satellite data on OLR acquired since 1980, relating this to local trends of increasing irrigation. If this hypothesis is found consistent with the data, current proposals to mitigate climate change by limiting combustion of fossil fuels may prove futile.

142

Theme 3: Climate 3.1 Changes in atmospheric circulation and Southern Hemisphere regional climate A novel investigation of the impact of anthropogenic forcing on the high- latitude southern hemisphere circulation Pope, James1, Marshall, Gareth1, Orr, Andrew1, Abraham, Luke2

Presenting author’s e-mail: [email protected]

1British Antarctic Survey, Cambridge, UK 2National Centre for Atmospheric Science-Chemistry, University of Cambridge, UK

Session 3.1 – February 6, 2018, 1100-1115

We examine the impact of the individual and combined effects of three anthropogenic forcings on high-latitude Southern Hemisphere circulation through a novel suite of climate model simulations. Using the UK Met Office Unified Model (UM) coupled to the UK Chemistry and Aerosols (UKCA) interactive climate-chemistry model, we investigate the circulation response due to ozone depletion, and increases in both greenhouse gases and anthropogenically-produced aerosols.

A suite of experiments, comprising a ‘control’ and seven further ‘perturbed’ runs, covering all possible individual and combinations of the three different forcings, were run for a period of 56 years, and the final 30 years used to produce a climatology. The control-run was forced by pre-industrial concentrations of greenhouse gases, ozone depleting substances, and aerosols, while the perturbed experiments comprised the control simulation plus fixed present-day values of one or more of the forcings. In order to properly separate the effect of the individual forcings, we applied a modification to the standard UM-UKCA configuration to partition the UM radiation scheme and the UKCA chemistry scheme: therefore, the chemical effects from greenhouse gases and the radiative forcing effects from ozone depleting substances are independent of each other within simulations having ozone and greenhouse gas perturbations.

We focus our results on the effect of the forcing(s) on the Southern Hemisphere Annular Mode (SAM), which is the principal mode of atmospheric variability at southern high latitudes, although we also analyse changes in meridional circulation around Antarctica, which play a major role in driving climate variability across the continent. Individual forcing responses in our model are consistent with previous studies. However, in contrast to some other studies, we find that the effect of the individual forcings are not linear when compared to the simulation combining all three forcings. Aerosols appear to play the largest role in driving this non-linearity.

143

Activity of the Southern Annular Mode during 2015-2016 El Niño event and its impact on Southern Hemisphere climate anomalies Osman, Marisol1, Vera, Carolina1

Presenting author’s e-mail: [email protected]

1Departamento de Ciencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera (CIMA), Instituto Franco-Argentino del Clima y sus Impactos (UMI-IFAECI) /CNRS, CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina

Session 3.1 – February 6, 2018, 1115-1130

In this work we analyzed the strong positive phase of the Southern Annular mode (SAM) observed during the El Niño event of 2015-2016 (EN15-16) and its impact on climate anomalies in the western portion of the Southern Hemisphere. Previous studies documented that El Niño (EN) events are in general associated with negative phases of the SAM. However, despite EN15-16 was one of the three strongest events ever recorded, it was associated with SAM positive phases of extreme intensity. Furthermore, while the negative linear relationship between ENSO and SAM during the most recent period (1986-2014) was significant and associated with a narrow uncertainty band, the combined condition of both climate patterns in the EN15-16 event was an outlier. In addition, while SAM anomalies during 2015 austral spring (September-October-November) can be attributed to the extreme negative ozone anomalies in the Southern Hemisphere (SH), the reasons for the strong positive anomalies in austral summer (December-January-February) are still unclear.

The EN15-16 influence on the austral summer circulation anomalies at the extratropical and polar regions of the SH was considerably altered by the strong SAM positive phase, which was evident not only at the troposphere but also at the stratosphere. The analysis of the geopotential heights anomalies at 200hPa reveals that in the EN15-16 event, large negative anomalies were well discernible over the Antarctica, that are typical of SAM positive phases. In addition, negative centers located over central and eastern portions of the south Pacific middle latitudes and the positive center extended to the west of the Antarctic Peninsula are shifted equatorward in the EN15-16 than in the other EN composites. Such circulation changes resulted in unusual regional impacts, like negative anomalies of surface air temperature in western Antarctic Peninsula, and negative precipitation anomalies in southeastern South America, ever recorded for previous strong EN events.

144

Changes in the mean meridional circulation and its impact on the climate of Victoria Lucas, Chris1, Dowdy, Andrew1, Nguyen, Hanh1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 3.1 – February 6, 2018, 1130-1145

The mean meridional circulation (MMC) is the planetary-scale circulation that acts to transport the excess of solar energy received in the equatorial regions to higher latitudes. An isentropic analysis of the MMC using data from the ERA-Interim reanalysis indicates that the MMC has been changing since at least 1979, particularly in the Southern Hemisphere (SH). The downward branch of the Hadley Cell (HC) has been moving poleward at a rate of about 0.5° decade-1 since that time; the HC in the SH is intensifying, concurrent with greater latent heating in the deep tropics and enhanced radiative cooling in the subtropics. Further, the portion of the MMC associated with the mid-latitude storm track has shown significant multi-year variability, with a strong drop in intensity in 1997 and a gradual return to its earlier strength by the mid-2010s. These changes are hypothesized to be caused by a combination of Antarctic ozone depletion, increased greenhouse gas concentration and natural variability.

Over the same period, the climate of Victoria has undergone large-scale change and episodic periods of strong variability. Events include the record dry of the Millennium Drought and the extreme seasonal precipitation events of 2010/11 and 2016. A long-term trend towards increasingly severe fire weather and the general drying of the climate in Victoria have resulted in issues around the management of land and water resources.

In this presentation, the relation between these broad-scale changes in the MMC and the regional climate of Victoria will be explored. How do the larger-scale changes drive the regional climate? This will be explored through an examination of the observed synoptic weather variability and the parameters of the MMC. The co-variability of these factors with other dominant modes of climate variability will be considered to isolate the effects of the changing MMC on the regional climate.

145

Detecting surface climate changes due to ozone change using ‘weather@home’ Nistor, Benjamin1, Rosier, Suzanne2, Renwick, James1

Presenting author’s e-mail: [email protected]

1Victoria University of Wellington, New Zealand 2National Institute of Water and Atmospheric Research, Wellington, New Zealand

Session 3.1 – February 6, 2018, 1145-1200

Stratospheric ozone depletion has been shown to influence the surface climate of the Southern Hemisphere during the austral summer season. Previous studies commonly describe the induced changes in terms of the documented strong association to Southern Annular Mode variability. This study utilises the power of distributed computing to assess if surface climate changes can be detected and attributed to ozone depletion in the ‘weather@home’ model. Very large ensembles of simulations are analysed for three scenarios: the anthropogenic world (all forcings appropriate to 2013), the anthropogenic world with prescribed ozone fields appropriate to 1959, and an estimate of the natural world (natural atmospheric forcings with removal of an estimate of the anthropogenic warming in SSTs). All of the scenarios are simulated using the global Hadley Centre Atmospheric Model HadAM3P with a higher resolution regional model (HadRM3P) embedded over the Australasian domain. During the austral summer, ozone changes appear be a major contributor to changes in mid-latitude climate, inducing significant changes in patterns of both tropospheric circulation and precipitation. Recovery of the ozone hole is however likely to work against the effects of anthropogenic warming on Southern Hemispheric mid-latitude circulation.

146

An energetic perspective into the variability of atmospheric circulations Boschat, Ghyslaine1,2, Simmonds, Ian1, Purich, Ariaan2,3, Graversen, Rune4

Presenting author’s e-mail: [email protected]

1School of Earth Sciences, University of Melbourne, VIC, Australia 2ARC Centre of Excellence for Climate Extremes 3CSIRO Oceans and Atmosphere, Aspendale, VIC, Australia 4The Arctic University of Norway, Tromsø, Norway

Session 3.1 – February 6, 2018, 1200-1215

The atmosphere and the ocean play a critical role in maintaining the Earth’s energy balance by transporting energy from the equator to the poles. In the atmosphere, processes are occurring on very different scales in space and time to ensure a ‘seamless’ transfer of energy: in the tropics most of the energy is transported poleward by the Hadley circulation, while eddies dominate the transports in mid-to-high latitudes.

This study aims to improve our understanding of the behaviour of atmospheric circulations, by providing a new estimate of energy transports and determining the relative role of large-scale and synoptic circulations in the global energy redistribution. Using 6-hourly outputs from ERA-Interim and CMIP5 model simulations, we examine the spatial contrasts in the transport of sensible heat, latent heat, potential and kinetic energy fields, and diagnose how these may have been changing on seasonal to inter-annual timescales. These contributions are further partitioned into mean meridional circulations and (stationary and transient) eddy activities, to explore the complementary variations occurring between high latitude synoptic systems and mean tropical cells. This energetic decomposition allows us to explore tropical-extratropical interactions within a “unifying” framework which takes into account the links between different atmospheric scales (both in space and time). It also provides new insights into the variability and trends of atmospheric circulations and how these are projected to change under a global warming scenario.

147

3.2 Tropical Indo-Pacific variability: dynamics, teleconnections and impacts Pacific meridional modes and tropical decadal variability: past and future Di Lorenzo, Emanuele1, Zhao, Yingying1, Liguori, Giovanni1, Joh, Youngji1

Presenting author’s e-mail: [email protected]

1Georgia Institute of Technology, GA, USA 2National Marine Fisheries Service, National Oceanographic and Atmospheric Administration, CA, USA

Session 3.2 – February 5, 2018, 1100-1115

Meridional Modes (MMs) are coupled ocean-atmosphere disturbances that are energized in the sub- tropics through the wind-evaporation-sea surface temperature (WES) thermodynamic feedback. In the Pacific, the growth and propagation of the MMs from the extra-tropics to the equatorial latitudes is recognized as an important mechanism for triggering El Niño Southern Oscillation (ENSO) and energizing ENSO-like decadal variability. Using observational and climate modeling data, we show that MMs propagating from both the southern and northern hemisphere explain a large and independent fraction of tropical decadal variance over the historical period 1940-2017. As the mean state of the tropics warms under anthropogenic forcing, the nonlinear relationship between sea surface temperature (SST) and evaporation amplifies the Wind-Evaporation-SST (WES) thermodynamic feedback, which in turn leads to more energetic MMs, stronger ENSO-like decadal variability, and a tighter coupling between tropics and extra-tropics. Consistent with this trend, MMs have played a key role in recent record-breaking anomalies associated with the North Pacific marine heatwave of 2014- 15 and the 2015-16 El Niño. Given that amplification of the WES is also predicted for other oceanic basins under a warming climate, the increase in ocean-atmosphere thermodynamic coupling may provide a robust physical framework to explore future changes in climate variability on global scales.

148

Understanding ENSO event precursors Neske, Sonja1,2, McGregor, Shayne1,2

Presenting author’s e-mail: [email protected]

1School of Earth, Atmosphere and Environment, Monash University, Clayton, Australia 2ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, Australia

Session 3.2 – February 5, 2018, 1115-1130

Our study examines the dynamics that drive changes in equatorial Pacific warm water volume (WWV), the metric which is thought to underlie the predictability of ENSO. A wind-forced oceanic shallow- water model for the period 1980-2016 is used to decompose the WWV signal into two components: (i) the adjusted response, which is found by letting the model evolve unforced for three months (after any wind excited Kelvin wave has reached the eastern boundary); and (ii) the instantaneous response, which is the instantaneous WWV change due to Ekman transports. For the pre-2000 period, both the instantaneous and adjusted responses have a similar influence on the WWV recharge and discharge processes. During the post-2000 period, however, the influence of the adjusted response on the discharge weakens and vanishes totally on the recharge. This leads to the dominance of the instantaneous response in the post-2000 period, which explains the shortening of the correlation lead time between WWV and ENSO SST from the pre- (~6-9 months) to the post-2000 (~3 months) period. Moreover, a strong lagged anti-correlation between WWV and ENSO SST was found for the pre-2000 period similar to that displayed by the adjusted response/ENSO SST lag correlation; however, this lagged correlation was missing for the post-2000 period due to the dominance of the instantaneous influence. These results support both, the self-sustained cyclic view of ENSO provided by theory and the view of ENSO as a series of event like disturbances that operate around a stable background; and suggests both are operating all the time. However, the relative role of each mechanism can vary through time, and appears to have changed to a regime more prominently driven by event like disturbances since the year 2000. This may explain the decrease in the predictability of ENSO events that has been reported during this recent period.

149

Global warm-to-cold ocean heat transport controlled by the Eastern Pacific Cold Tongue Holmes, Ryan M.1,2, Zika, Jan D.2, England, Matthew H.1

Presenting author’s e-mail: [email protected]

1ARC Centre of Excellence for Climate System Science and the Climate Change Research Centre, University of New South Wales, NSW, Australia 2School of Mathematics and Statistics, University of New South Wales, NSW, Australia

Session 3.2 – February 5, 2018, 1130-1145

The rate at which the ocean moves heat from the tropics towards the poles, and from the surface towards depth, depends on diabatic processes associated with surface forcing and diffusive mixing. Here, we use a global ocean sea-ice model at two horizontal resolutions (1/4° and 1/10°) to quantify the transport of heat across temperature classes (i.e. the diathermal ocean heat transport). Such an approach removes the effects of adiabatic advection and isolates the competition between surface forcing, which acts to increase temperature contrasts within the ocean, and the homogenisation of ocean temperatures through diffusive mixing. By examining the spatial and temporal structure of the diathermal processes, we find that much of the global net flux of heat across temperature classes between 15°C and 25°C is driven by intense mixing in the eastern equatorial Pacific during austral spring. This region, covering less than 2% of the ocean's surface area, is a hot spot for ocean heat uptake due to a large air-sea heat flux, a shallow, intense thermocline and strong wind- and shear- driven turbulence. These results have implications for the role of small-scale processes in global climate and the variability of ocean heat uptake over interannual and decadal time-scales.

150

Inability of CMIP5 climate models to simulate recent multi-decadal temperature change in the pacific Power, Scott1, Delage, François1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Australia

Session 3.2 – February 5, 2018, 1145-1200

Future changes to both year-to-year climatic variability in the Pacific linked to ENSO, and changes in long-term average climate about which the variability will occur, are projected in response to “business-as-usual” increases in greenhouse gas emissions. While mean-state and variability changes have been studied separately, very little is known about their combined impact or relative importance. Studies of projected changes in ENSO have also tended to focus on changes in, or adjacent to, the Pacific. Here we examine projected changes in both climatic conditions during El Niño and La Niña years relative to 20th century mean-state conditions, and in ENSO-driven precipitation variability about 21st century mean-state conditions. We examine changes over the globe, derived from 36 CMIP5 models forced according to the RCP8.5 scenario in which there are large, unmitigated increases in greenhouse gas concentrations during the 21st century. We show that precipitation variability associated with ENSO is projected to increase in the tropical Pacific. However, while increases are evident in many regions away from the Equatorial Pacific, the increases are modest, and are robust in only a handful of regions. We also show that projected changes in the magnitude of El Niño-driven climatic anomalies in the regions analysed are much smaller than projected changes in average climate in nearly all locations.

151

“Statistical Challenges in Climatology”: Outcomes from a joint Bureau of Meteorology/ACEMS workshop Grainger, Simon1, Frederiksen, Carsten1,2

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia 2Monash University, VIC, Australia

Session 3.2 – February 5, 2018, 1200-1215

For understanding the impact of tropical teleconnections on regional climate, a useful conceptual model is to consider climate variables as comprising of quickly- and slowly-varying components, respectively climate “noise” and a potentially predictable “signal”. Here, we apply this conceptual model to first estimate the potential predictability of Australian winter (June-July-August) mean rainfall, and then to relate the potential predictability to major processes responsible for interannual climate variability.

Winter rainfall for the period 1957-2015 is obtained for a sub-sample of 800 stations from the Bureau of Meteorology’s observation network. The stations are long-term sites (most have more than 50 years of data), and are as evenly distributed as the full network allows. Interannual variability of the seasonal mean is separated into intraseasonal (“noise”) and slowly-varying (“signal”) components. Potential predictability is defined as the ratio of the signal variability to the total interannual variability. It is found that the highest winter rainfall potential predictability is over central Australia, and extending to the southeast.

The station time series are then coupled with atmospheric fields from reanalysis data to describe the related teleconnections. The dominant mode in the signal component shows a downward trend in southern Australian rainfall, coupled to circulation changes reflecting the extratropical response to tropical thermal expansion. The second mode is strongly related to extremes in Australian mean rainfall. High (low) mean rainfall is shown to be connected to high (low) sea surface temperatures in the Maritime Continent, and consequent enhanced (reduced) onshore flow from northwestern Australia. A third mode related to the meridional Indian Ocean dipole has a secondary effect on enhancing potential predictability.

The utility of the conceptual model is demonstrated by considering the Australian winter rainfall for 2016 and 2017.

152

Multi-year ENSO prediction Luo, Jing-Jia1, Nguyen, Hanh1, Hendon, Harry1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 3.2 – February 5, 2018, 1445-1500

El Niño and La Niña strongly affect the year-to-year variability of Australian climate, which exerts intense pressure on water resources and environmental management. Well-known examples include the severe floods in 2010-11 and 1998-2000 in association with multi-year persistent La Niña events, and strong drought in 2002 in association with El Niño. Growing evidence suggests that some ENSO events may be predictable at lead times beyond one to two years, which is longer than the forecasts currently issued by most operational forecast centres worldwide. However, it is still unclear how well ENSO can be predicted at multi-year time scales and what essential dynamics underpins such multi- year predictability. In collaboration with Sydney Water and the UK Met Office, three sets of ensemble multi-year hindcasts were produced using the high-resolution ocean-atmosphere coupled model, ACCESS-S. The first set of experiments contain 30-member ensemble predictions of 16 target months starting 1 November for every year during the period 1980-2014. The second set of experiments consist of 10-member ensemble predictions of 66 target months starting 1 November every 2-3 years during the period 1960-2014. The third set of experiments involves using 23 ensembles of 36-month predictions to examine the multi-year predictability of the back-to-back La Niña during 1998-2001 and the 2002-03 central-Pacific El Niño event. Results suggest that, despite considerable model bias in simulating the annual cycle of the Indo-Pacific climate, ENSO over the past 35 years can be skilfully predicted out to 16 months ahead consistently. Some ENSO events can be well predicted with a 3- year lead. In addition, the results also show good skill in predicting global warming related signals at multi-year timescales. Without any downscaling, the high-resolution model also displays encouraging skill in predicting both climate mean states and anomalies around the Sydney Water basin at multi- annual timescales.

153

Future changes in Extreme El Nino events modulated by North Tropical Atlantic variability Ham, Yoo-Geun1, Kug, Jong-Seong2, Yang, Woo-Hyun2, Cai, Wenju3

Presenting author’s e-mail: [email protected]

1Faculty of Earth Systems and Environmental Sciences, Chonnam National University, Gwangju, South Korea 2School of Earth Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, South Korea 3CSIRO Marine and Atmospheric Research, Aspendale, Victoria 3195, Australia

Session 3.2 – February 5, 2018, 1500-1515

The extraordinarily strong El Nino events, such as those of 1982/83, 1997/98, and 2015/16 are known to cause critical socio-economic impacts world-wide by disrupting global weather patterns, cyclones, drought/floods, and ecosystems. Therefore, it is a critical question how often such extreme El Nino will take place in a future. Athough many climate models tend to simulate more frequency extreme El Nino under the greenhouse warming, there is a large inter-model diversity, with a range as large as the multi-model averaged change. The cause for this inter-model uncertainty is not known. Here we show that the North Tropical Atlantic (NTA) mean precipitation plays a significant role in controlling changes in the extreme El Nino frequency under global warming; that is, much frequent extreme El Nino events under the greenhouse warming will be observed in the models whose climatological precipitation over the NTA is largely decreased. Relatively drier climatology over the NTA can induce a wetter climatology over the equatorial eastern Pacific through an atmospheric teleconnection, and it provides background condition that the El Nino-related convective responses is amplified to push the El Nino to the extremes.

154

Causes and predictability of the negative Indian Ocean Dipole and its impact on La Niña during 2016 Lim, Eun-Pa1, Hendon, Harry1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 3.2 – February 5, 2018, 1515-1530

In the second half of 2016, Australia and Indonesia experienced extreme wet conditions and East Africa suffered extreme dry conditions, which were largely attributed to the occurrence of strong negative Indian Ocean dipole (IOD) and weak La Niña. This study is aimed at exploring the causes and predictability of the strong negative IOD and its impact on development of La Niña in 2016 by analysing atmosphere and ocean reanalyses and conducting forecasts sensitivity experiments using the Australian Bureau of Meteorology’s dynamical seasonal forecast system. The results show that the strong negative IOD of 2016 peaked in July to September, and the key drivers of its development were the subsurface ocean wave dynamics and anomalous westerly wind bursts in April to June in the tropical Indian Ocean. However, the long-term trend over the last 55 years in sea surface and subsurface temperatures in April, which is characterised by warming of the tropical Indian and western Pacific and cooling in the equatorial eastern Pacific, contributed positively to the extraordinary strength of this IOD event. This strong negative IOD appears to have been a key promoter of the weak La Niña of 2016. Without the remote forcing from the negative IOD, this weak La Niña may not have eventuated, despite encouraging subsurface and wind conditions that were set up by the extraordinarily strong El Niño of 2015-16.

155

Regional changes to the remote impacts of the El Niño-Southern Oscillation Perry, Sarah1,2,3, McGregor, Shayne2,3, Sen Gupta, Alex1,3, England, Matthew1,3

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2Monash University, VIC, Australia 3ARC Centre of Excellence for Climate System Science

Session 3.2 – February 5, 2018, 1530-1545

Climate variability in the tropical Pacific Ocean associated with the El Niño-Southern Oscillation (ENSO) effects remote regions around the world through atmospheric teleconnections. Under twentieth century climate conditions, ENSO’s modulation of interannual climate has contributed to significant and sometimes severe societal impacts. Whether the remote effects of ENSO will change as the climate continues to warm in the coming decades is therefore an important component of regional climate change projections.

Here we investigate how ENSO’s temperature and precipitation teleconnections are projected to change in the high-emission RCP8.5 simulations of 40 CMIP5 models.

Our recent study has shown that there is robust intermodel agreement on an increase in the spatial extent of ENSOs teleconnections over land areas globally. However, when comparing the magnitude of historical and future teleconnections in the regions which show the strongest intermodel agreement, the models don’t show a consistent change in the teleconnection strength in the latter half of the 21st century. Instead, we will show that the models project both strengthening, weakening, and no change, of ENSOs teleconnections occurring at different regions with strengthened teleconnections occurring in Australia, central and eastern Africa, and South America. We further explore the changes in atmospheric dynamics in the individual models that may be giving rise to these changes in the magnitude of ENSOs teleconnections.

156

ENSO diversity in CMIP5 models and its relation to co-varying dynamics Wengel, Christian1, Dommenget, Dietmar2, Bayr, Tobias1, Latif, Mojib1,3

Presenting author’s e-mail: [email protected]

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany 2School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria, Australia 3University of Kiel, Kiel, Germany

Session 3.2 – February 5, 2018, 1645-1700

Model simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) show large diversity in the strength of El Niño/Southern Oscillation (ENSO) variability, which is, surprisingly, unrelated to ENSO growth rate as defined by the Bjerknes Stability (BJ) index, a measure of sea surface temperature anomaly growth rate. Here we show that this peculiarity is due to co-variations of ENSO dynamics in the linear recharge oscillator model, i.e. between the growth rate of sea surface temperature anomalies (T) and upper ocean heat content anomalies (h), coupling between T and h and stochastic noise forcing of T and h. The co-varying dynamics modulate ENSO amplitude and span a broad range of ENSO behaviour. We show that the combined effect of the co-varying dynamics helps to understand ENSO amplitude diversity in the CMIP5 models. These results also explain why the BJ index must not necessarily correlate with ENSO amplitude and that it may not serve as a reliable tool to investigate ENSO amplitude diversity in a multi-model ensemble.

157

Has El Niño changed its flavour? Recent changes in a multi-century context Freund, Mandy1,2, Henley, Benjamin J.1,2, Karoly, David J.1,2

Presenting author’s e-mail: [email protected]

1School of Earth Sciences University of Melbourne, Melbourne, VIC, Australia 2ARC Centre of Excellence for Climate System Science

Session 3.2 – February 5, 2018, 1700-1715

El Niño-Southern Oscillation (ENSO) is a central feature of the climate system, with severe impacts on ecosystems and human societies. In particular, anomalously warm (El Niño) conditions in the tropical Pacific are associated with changes in atmospheric circulation, with associated changes to global teleconnection patterns. Recent studies have suggested major possible changes are under way with respect to the frequency and intensity of ENSO events. Under greenhouse warming scenarios an increase in frequency of extreme El Nino and La Nina events is projected. El Niño events can differ substantially in their spatial pattern, amplitude, temporal evolution and therefore its impacts. Recent work has identified different ‘flavours’ of ENSO, for example, classical cold-tongue ENSO events and non-conventional El Niño definitions like the Central Pacific, Modoki and warm pool El Niño events. Large uncertainties still persist on how individual flavours of El Niño could be affected under climate change. A critical question is to understand the sequence, relative frequency and dynamics of ENSO events prior to the instrumental period. Model studies suggest that with continued greenhouse warming, Eastern Pacific El Niño events will become less frequent, and central Pacific El Niño events will increase. This has been observed in instrumental records. However, short instrumental records, pronounced decadal variability and a high degree of diversity in climate model projections limit our ability to contextualise recent changes and evaluate possible future changes under global warming.

Here we use a network of seasonally-resolved coral data to reconstruct El Niño event types several centuries into the past. Comparison with instrumental observations and existing ENSO reconstructions exhibits high agreement on interannual timescales and highlights the merit of seasonally-resolved proxies in studying ENSO dynamics. The reconstructions are used to explore the multi-centennial context of recent changes in the relative frequency of ENSO flavours.

158

The impact of strong El Niño events on east Australian spring rainfall van Rensch, Peter1,2,3, Arblaster, Julie1,4,5, Gallant, Ailie1, Cai, Wenju2, Nicholls, Neville1

Presenting author’s e-mail: [email protected]

1Earth, Atmosphere and Environment, Monash University, Victoria, Australia 2CSIRO, Aspendale, Victoria, Australia 3ARC Centre of Excellence for Climate Systems Science, Australia 4National Center for Atmospheric Research, Colorado, USA 5ARC Centre of Excellence for Climate Extremes, Australia

Session 3.2 – February 5, 2018, 1715-1730

El Niño typically leads to less than average springtime rainfall in eastern Australia, but at times the rainfall totals have not scaled with El Niño intensity. This is highlighted by the near average east Australian spring rainfall during the 1997 strong El Niño, when less than average rainfall was expected. Here we examine 50-member ensembles of SST-forced ACCESS 1.3 experiments to examine the teleconnection of strong El Niño events to east Australian rainfall. We find that the impact of strong El Niño on east Australian spring rainfall are highly dependent on the precise location of SST forced pressure anomalies to the south of Australia, and at times, their interaction with other adjacent pressure anomalies. For example, the 1997 El Niño event was associated with a high pressure anomaly to the south of Australia, typical of El Niño, however this event was also associated with a significant pressure anomaly to the north of Australia. These two high pressure anomalies interacted, causing a near average pressure gradient over eastern Australia, promoting an average circulation conducive to near average rainfall in the region. During the 1982 strong El Niño, a significant spring rainfall deficit was observed in east Australia, which we attribute to significant southeasterly wind anomalies over the region. The southeasterly wind anomalies were influenced by the location of the south of Australia high pressure anomaly, and also influenced by significantly cool SSTs to the northeast of Australia. A spring rainfall deficit was also seen during the 2015 El Niño event, but the mechanism appears more stochastic in origin. The 2015 model ensemble mean could not match the observed circulation pattern, whereas the ensemble mean could reproduce the 1982 and 1997 patterns. This suggests that the circulation – and therefore rainfall – during the 2015 event are unlikely of SST origin.

159

A potential for La Nina-like climate change in the ENSO Recharge-Oscillator framework Dommenget, Dietmar1, Vijayeta, Asha1

Presenting author’s e-mail: [email protected]

1Monash University, School of Earth, Atmosphere and Environment, Clayton, Australia

Session 3.2 – February 5, 2018, 1730-1745

Current projections of climate change suggest an El Nino like climate change with a weakening and eastward shift of the Walker circulation. While, the models do have some agreement on this, it does disagree with the observed changes, it is not understood why the model do this and it needs to be noted that current state-of-the-art climate models have common biases that may support an El Nino like warming bias. In this study, we present analysis of ENSO changes in the recharge oscillator (ReOsc) frame work. Using the ReOsc framework we will illustrate that CMIP model changes suggest significant changes in the ENSO dynamics. We will further illustrate that the ENSO ReOsc model within a fully complex atmosphere model will respond to global warming by a strong La Nina like cooling due to enhanced easterly wind forcings.

160

3.3 Maritime Continent earth system science for improved understanding and prediction of its local variability and global impact Intraseasonal variation in convective and stratiform rain in the Maritime Continent Vincent, Claire1, Lane, Todd1

Presenting author’s email: [email protected]

1ARC Centre of Excellence for Climate System Science and School of Earth Sciences, the University of Melbourne, Parkville, Australia

Session 3.3 – February 8, 2018, 1445-1500

Recent focus on changes in the diurnal precipitation cycle with the propagation of the MJO have motivated attempts to understand the physical feedbacks between mesoscale and intraseasonal scale variability in the Maritime Continent. The diurnal precipitation cycle, however, reflects the aggregate contributions of convective and stratiform processes, each with a qualitatively different signature of diabatic heating. In this work, we consider the distinct evolution of convective and stratiform rain over the Maritime Continent, both from convection-permitting simulations from the Weather Research and Forecasting (WRF) model and TRMM satellite observations.

Although there is no explicit separation of convective and stratiform rainfall in the WRF model, convective and stratiform processes exist and can be separated by consideration of surface rain-rates, updraft strengths, precipitation top heights and elevated rain water mixing ratio. Implementation of a convective-stratiform separation algorithm yields convincing profiles of latent heating pertaining to both deep and shallow convective and stratiform precipitation. WRF latent heating profiles are compared with analogous profiles from the TRMM spectral latent heating product.

Analysis of both simulated and observed latent heating profiles indicates that area averaged latent heating from convective precipitation reaches a maximum 1-2 phases ahead of that from stratiform rain, consistent with the observed peak in the diurnal precipitation cycle over the land ahead of the main MJO envelope. The analysis indicates a greatly enhanced role of stratiform processes over the sea to the north and south of Sumatra during the MJO active phases relative to the inactive phases. These result provide evidence that the aggregate diabatic processes that sit at the nexus of mesoscale and intraseasonal scale interactions rely on a correct partitioning between convective and stratiform precipitation.

161

Sea surface salinity variations in the Maritime Continent region and the relationships with monsoon, El Nino, and ocean currents Lee, Tong1, Fournier, Severine1

Presenting author’s e-mail: [email protected]

1Jet Propulsion Laboratory, California Institute of Technology, California, USA

Session 3.3 – February 8, 2018, 1500-1515

Variations of sea surface salinity (SSS) in the Maritime Continent (MC) region have important implications to ocean circulation and potentially to air-sea interaction. Systematic monitoring of salinity changes in the MC region has been extremely challenging due to the complicated geometry and other factors. This has hindered our understanding of freshwater changes in the MC region, the relationships with climate variability and the water cycle, and the potential implications to climate prediction from sub-seasonal to interannual time scales. NASA’s Soil Moisture Active Passive (SMAP) satellite has been providing sea surface salinity (SSS) measurements at 40-km spatial resolution and 8-day repeat cycle since April 2015. Here we examine seasonal-to-interannual variations of SSS in the MC region using SMAP SSS in relation to other satellite observations, including surface currents, precipitation, and soil moisture. The analysis results illustrated the relationships of SSS variations with monsoonal forcing in the northern and southern parts of the MC region, the effects of the 2015-16 El Nino and the consequence on the exchange between the MC and the Pacific, and observational evidence for the upper-ocean “freshwater plug” effect on the Indonesian throughflow.

162

Diurnal cycle of convection and circulation: weather-climate processes over the Maritime Continent Chen, Shuyi1, Savarin, Ajda1, Kerns, Brandon1

Presenting author’s e-mail: [email protected]

1University of Washington, Seattle, WA, USA

Session 3.3 – February 8, 2018, 1515-1530

It has been well documented that the diurnal maximum of convection and precipitation is observed during the morning hours (AM) over the ocean, whereas the maximum is during the afternoon hours (PM) over land. However, the difference between AM and PM precipitation in the coastal/adjacent seas over the Maritime Continent (MC) is 2-3 times larger than anywhere else in the tropics. This study explores the effects of varying diurnal surface forcing on the convection and circulation on various time scales over the MC. A high-resolution coupled atmosphere-ocean model is used to investigate the physical processes associated with variations of landmass, topography, and sea surface temperature. Coupled model experiments are conducted with flattened islands, removal of landmasses, and varying upper ocean temperatures mimicking conditions of climate change.

163

Assessing the impacts of coupling frequency on rainfall over the western Maritime Continent Li, Yue1, Jourdain, Nicolas C.2,3, Taschetto, Andréa S.1, Holland, Greg4, Done, James4, Sen Gupta, Alex1

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, NSW, Australia 2Centre National de la Recherche Scientifique, LGGE, F-38041 Grenoble, France 3Univ. Grenoble Alpes, LGGE, F-38041 Grenoble, France 4NCAR Earth System Laboratory, Mesoscale and Microscale Meteorology Division, Regional Climate Research, Boulder, CO, U.S.

Session 3.3 – February 8, 2018, 1645-1700

The Maritime Continent (MC) is sited within tropical western Pacific warming pool, where considerable latent heat associated with massive convective activities has profound influence on global circulations. Numerous previous studies have found that local air-sea interaction in MC plays an important role in large-scale circulation, yet it is recently recognised that high-frequent air-sea exchange can be important to rectification of longer timescale variation.

To quantify the effect of air-sea interaction on rainfall variability, we conducted a set of simulations in the MC region by changing coupling frequency (CF) of model. Results show that CF has significant influence on mean state and diurnal cycle of rainfall over the western MC during Indian monsoon season. Reducing CF can cause the increase of mean SST along the southwest off Sumatra by ~2°C in five consecutive months from June to October. It is speculated to be associated with deepening of thermocline along the coast due to anomalous downwelling equatorial Kelvin waves triggered by westerly anomaly along eastern equatorial Indian Ocean. In the meantime, the mean of rainfall in that area is largely increased. Although the CF has barely impacts on timing of diurnal cycle, it shows considerable influence on amplitude of diurnal cycle with decreased (increased) amplitude over North (South) Sumatra during Indian monsoon season when decreasing CF.

164

Maritime Continent land-sea breeze structure revealed by scatterometer data Short, Ewan1, Vincent, Claire1, Lane, Todd1

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia

Session 3.3 – February 8, 2018, 1700-1715

The land-sea breeze circulation (LSBC) plays a significant role in convection, particularly in the tropics where the weak Coriolis force allows land and sea breezes to propagate hundreds of kilometers both inland and offshore. Convection in the Maritime Continent is especially sensitive to the LSBC due to the large number of islands present and the high topography of many of these islands. In previous work it has been argued that the underrepresentation of these features in coarse resolution climate models leads to significant heating and rainfall biases which affect circulation throughout the tropics and mid-latitudes. Moreover, higher resolution mesoscale models are known to exhibit errors in the timing and intensity of the diurnal precipitation cycle and LSBC in this region. In this study I have investigated the LSBC throughout the whole Maritime Continent region using four satellite scatterometer datasets which span 2012-2017. Scatterometers are remarkable instruments capable of inferring ocean surface winds by emitting a spectrum of microwave radiation and analysing the backscatter off the ocean surface for constructive interference with wind-induced capillary waves. Variations with season and MJO phase have also been examined, and comparisons with the Weather Research and Forecasting Model, and the Tropical Rainfall Measurement Mission data have been performed. The study reveals fascinating observed variation in the timing, intensity and offshore extent of the LSBC across different parts of the Maritime Continent – results that have hitherto relied on high-resolution numerical simulations. The results build on previous work on the diurnal cycle of tropical precipitation, and how this diurnal cycle interacts with the MJO.

165

Intraseasonal oscillations and embedding convection-coupled disturbances in South China Sea and surrounding areas Sui, Chung-Hsiung1, Lin, Po-Hsiung1

Presenting author’s e-mail: [email protected]

1National Taiwan University, Taipei, Taiwan

Session 3.3 – February 8, 2018, 1715-1730

We made special observations in December 2016 and May-June 2017 in the South China Sea (SCS) in preparation for the SCS Two-Island Monsoon Experiment (SCSTIMX). Combining the special data and existing reanalysis and satellite data, we are analyzing the Evolution of diurnal to intraseasonal scale of oscillations over the SCS and Maritime Continent (MC) and the embedding convective processes. A systematic analysis of the December 2016 shows evolution of Kelvin waves (KW), equatorial Rossby waves (ER), mixed Rossby-gravity/TD-type (MRG/TD) waves in a La Nina climate background with warmer SST and enhanced convection over western Pacific, MC, and eastern Indian Ocean. Interaction between tropical waves, synoptic scale weather systems and topography is evident and may leads to formation or intensification of other systems, like KW, tropical storm Nock-ten and Yvette, and others. Propagation of the Kelvin Wave coincides with Australian summer monsoon onset in mid-December. Besides the analysis of December 2016, we also carry out a composite analysis of moisture static energy budget in the Indian Ocean, SCS, and western Pacific areas based on reanalysis data. The budget analysis show that low-level moisture advection (Kelvin wave dynamics) and horizontal moisture advection are all important for the propagation of instraseasonal oscillations (ISO), and longwave radiation and air-sea flux at surface tend to destabilize ISOs. In addition, northward propagation for boreal summer ISOs is primarily contributed by moisture advection and boundary layer convergence produce by vortex twisting.

166

Predictable patterns of rainfall and atmospheric circulation over the Maritime Continent and adjacent regions: role of air-sea interaction and seasonal dependence Yang, Song1, Zhang, Tuantuan1, Huang, Bohua2, Kinter, James2, Laohalertchai, Charoon3

Presenting author’s email: [email protected]

1Sun Yat-sen University, Guangzhou, China 2George Mason University, Virginia, USA 3Thai Meteorological Department, Bangkok, Thailand

Session 3.3 – February 8, 2018, 1730-1745

Prediction skills of rainfall and atmospheric circulation over the Maritime Continent and adjacent regions (MCAR) are studied using the reforecasts from the NCEP CFS and the Minerva project. A maximum signal-to-noise empirical orthogonal function (MSN EOF) analysis indicates that the most predictable patterns of MCAR climate are associated with the developing and maturing phases of ENSO. The other predictable processes are more seasonally dependent. For winter and spring, the second most predictable patterns are associated with the ENSO decaying phase, and the monthly evolution of the patterns is characterized by a southward shift of westerly anomalies, generated by the interaction between the annual cycle and ENSO signals. In summer, the second predictable patterns are associated with the western North Pacific monsoon in short leads and with ENSO in longer leads. The second predictable patterns in fall are mainly associated with tropical Indian Ocean Dipole.

Intra-ensemble variability shows a large seasonality that affects different predictable patterns in different seasons. The dominant patterns of ensemble spread initialized in May bear some resemblance to the predictable monsoon patterns in summer and the ENSO patterns in fall, reflecting the noise-induced differences in the evolution of predictable signals among ensemble members. The noise patterns for initialization in November are dominated by northern extratropical atmospheric perturbations from winter to spring, expanding southward through a coupled footprinting mechanism to perturb ENSO evolution in different ensemble members. The extratropical perturbations in the Southern Hemisphere, most significant in early months with May-initialized predictions, are less effective in affecting tropical circulation.

The MCAR climate is more predictable during the dry season than during the wet season. The prediction skill is higher for the eastern MC than for the western MC. The regional feature of prediction skill is related to the relative importance of ENSO forcing and local air-sea interaction.

167

3.4 South American climate variability, change and predictability Testing for collective significance of temperature trends Huth, Radan1,2, Dubrovský, Martin2,3

Presenting author’s e-mail: [email protected]

1Charles University, Prague, Czechia 2Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, Czechia 3Global Change Research Institute, Brno, Czechia

Session 3.4 – February 6, 2018, 1645-1700

A common way of assessing long-term trends in climate elements at individual sites (stations or gridpoints) is to conduct separate local significance tests at each site, without any attempt to evaluate whether the number of individual local tests that are found significant could (or could not) occur by chance at a given significance level. That is, the issue of collective (global, field) significance in the context of testing for climatic trends has been overlooked almost completely. Additionally, insignificant local (station) trends are often ignored in climate change detection studies, which results in a considerable loss of potentially useful information.

In order to avoid this gap, we evaluate several tests for field significance on synthetic datasets, generated by multi-site stochastic generator SPAGETTA (SPatial GEneraTor for Trend Analysis). These tests are based on: (i) counts of locally significant tests, (ii) lowest p-value of all local tests (Walker test), (iii) false discovery rate (generalization of the Walker test); (iv) generalized Mann-Kendall test; and (v) counts of positive and negative trends regardless their local significance (which has been proposed and developed by us). The evaluation is conducted on synthetic data defined on a regular grid with various values of spatial and temporal autocorrelation and for various values of trend, which are all spatially uniform. The sensitivity of results of statistical testing to the length of the series and to the proportion between autocorrelation distance and the density of the station network / grid is assessed.

The tests are then applied to real temperature data in Southern Hemisphere, both station and gridded. The tests of collective significance confirm that temperature trends were positive since the half of the 20th century.

168

Rainfall variability over South America associated with SST anomalies in South Pacific and South Atlantic oceans Eidt, Renata T.1, Cavalcanti, Iracema F. A.1

Presenting author’s email: [email protected]

1National Institute for Space Research - INPE, SP, Brazil

Session 3.4 – February 6, 2018, 1700-1715

Sea surface temperature (SST) anomalies influence atmospheric circulation and contribute to changes in weather and climate around the globe. It is already known that precipitation over continental areas can be associated with SST variability in the tropics. However, the importance of extratropical oceans is still not completely understood. The aim of this study is to investigate the influence of extratropical SST anomalies to rainfall variability, focusing on South America, and the oceanic and atmospheric processes involved. The period from 1981 to 2010 was studied in a monthly scale, using SST and precipitation data obtained from NOAA datasets (ERSST-v5 and GPCP, respectively), and atmospheric data from CFSR reanalysis. Singular Value Decomposition (SVD) showed connectivity between SST variations in extratropical oceans and rainfall variability over southeastern South America, an important agricultural area. Extreme wet and dry events over this region were identified using the Standardized Precipitation Index (SPI), to a further evaluation of the oceanic conditions associated with these episodes. Empirical Orthogonal Functions (EOF) and SVD were applied for the identification of principal modes of variability. Dipoles of SST were identified in South Pacific and South Atlantic oceans. Two areas of opposite signs were observed in western (~25°S) and southern (~55°S) South Pacific Ocean, regions of atmospheric blocking and the South Pacific Convergence Zone (SPCZ). Positive SST anomalies in the southern area are related to precipitation increase over southeastern South America. The southern oceanic area is also associated with a dipole of precipitation over Southeast Asia and central Pacific Ocean. A dipole signal was also noticed in western South Atlantic Ocean, mainly from September to December, varying in position and intensity near South America. The results obtained showed that extratropical oceans have an important role for precipitation variability in remote regions, and the oceanic areas identified can contribute to climate monitoring.

169

Air-sea interactions in the Western South Atlantic and regional climate impacts Goes, Marlos1,3, Siqueira, Leo2, Foltz, Greg3, Kirtman, Ben2

Presenting author’s e-mail: [email protected]

1University of Miami/CIMAS, FL, USA 2University of Miami/RSMAS, FL, USA 3NOAA/AOML, FL, USA

Session 3.4 – February 6, 2018, 1715-1730

This study examines the role of increased ocean resolution and air-sea interaction in the western South Atlantic using observations and two 150-year climate model simulations with identical atmospheric resolution but contrasting ocean resolutions. Regardless of the differing ocean resolution, both models were able to reproduce the observed DJF rainfall variability over Subtropical South America as well as the leading modes of coupled SST/high cloud anomalies. The large-scale teleconnections from the Pacific to the western South Atlantic are broadly consistent between the two simulations. However, many of the regional details, particularly associated with local air-sea interactions and the Brazil Current, are markedly different. Specifically, anomalous dry and wet areas along the coast in the ocean eddy-resolving coupled model are not linked to the large-scale atmospheric forcing, but rather to anomalous SST associated with variability in the strength of Brazil Current. The dominant differences include a large reduction in convective precipitation along the subtropical shelf due to colder near-coastal SSTs and reduced turbulent heat fluxes during periods when the western South Atlantic is anomalously warm due to ENSO teleconnections. Ocean temperature sections near the coast also show large differences, with the eddy-resolving model in better agreement with observational estimates. Finally, we examine the coupled air-sea mechanisms in the western South Atlantic regarding the most efficient processes to drive atmospheric convection and precipitation.

170

Impact of atmospheric blocking on South America in austral summer Rodrigues, Regina1, Woollings, Tim2

Presenting author’s e-mail: [email protected]

1Federal University of Santa Catarina, Florianopolis, Brazil 2AOPP, University of Oxford, Oxford, United Kingdom

Session 3.4 – February 6, 2018, 1730-1745

In this study, we investigate atmospheric blocking over east South America in austral summer for the period of 1979-2014. Our results show that blocking over this area is a consequence of propagating Rossby waves that grow to large amplitudes and eventually break anticyclonically over subtropical South America (SSA). The SSA blocking can prevent the establishment of the South Atlantic Convergence Zone (SACZ). As such, years with more blocking days coincide with years with fewer SACZ days and reduced precipitation. Convection mainly over the Indian Ocean associated with Madden- Julian Oscillation (MJO) phases 1 and 2 can trigger the wave train that leads to SSA blocking whereas convection over the western/central Pacific associated with phases 6 and 7 is more likely to lead to SACZ events. We find that MJO is a key source of long-term variability in SSA blocking frequency. The wave packets associated with SSA blocking and SACZ episodes differ not only in their origin but also in their phase and refraction pattern. The tropopause-based methodology used here is proven to reliably identify events that lead to extremes of surface temperature and precipitation over SSA. Up to 80% of warm surface air temperature extremes occur simultaneously with SSA blocking events. The frequency of SSA blocking days is highly anti-correlated with the rainfall over southeast Brazil. The worst droughts in this area, during the summers of 1984, 2001 and 2014, are linked to record high numbers of SSA blocking days. The persistence of these events is also important in generating the extreme impacts.

171

3.5 Climate of the tropical Pacific Islands Diurnal variations of rainfall in surface and satellite observations at a summer monsoon coast Chen, Guixing1, Lan, Ruoyu1, Zeng, Wenxin1, Pan, He1, Li, Weibiao1

Presenting author’s e-mail: [email protected]

1Center for Monsoon and Environment Research, School of Atmospheric Sciences, and Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, China.

Session 3.5 – February 7, 2018, 1130-1145

The complex features of rainfall diurnal cycles at South China coast are examined using hourly rain- gauge data and satellite products (CMORPH and TRMM-3B42) during 1998–2014. It is shown that morning rainfall is pronounced near the coasts and windward mountains with high rainfall in the summer monsoon season, while afternoon rainfall is dominant on land and nocturnal rainfall occurs at northern inland sites. Both satellite products report less morning rainfall and more afternoon rainfall than rain-gauge data, and they also miss the midnight rainfall minimum. These errors are mainly attributable to an underestimation of morning moderate/intense rains at coasts and an overestimation of afternoon–evening light rains on land. With a correction of systematic bias, satellite products faithfully resolve the spatial patterns of normalized rainfall diurnal cycles related to land-sea contrast and local terrains, suggesting an improved data application for regional climate studies. In particular, they are comparable to rain-gauge data in showing the linear reduction of morning rainfall from coasts to inland regions. TRMM is marginally better than CMORPH in revealing the overall features of diurnal cycles, while higher-resolution CMORPH captures more local details. All three datasets also present that morning rainfall decreases from May–June to July–August especially on land; it exhibits pronounced interannual variations and a decadal increase in 1998–2008 at coasts. Such long-term variations of morning rainfall are induced by the coastal convergence and mountain liftings of the monsoon shear flow interacting with land breeze, which is mainly regulated by the monsoon southwesterlies in the northern part of the South China Sea.

172

Modelling extreme precipitation in the tropical South Pacific: A case study over New Caledonia Brown, Andrew1,2, Nguyen, Hanh1, Peltier, Alexandre3, Vincent, Claire4,5, Bellon, Gilles2

Presenting author’s e-mail: [email protected]

1Australian Bureau of Meteorology, VIC, Australia 2University of Auckland, New Zealand 3Météo-France, New Caledonia 4The University of Melbourne, VIC, Australia 5ARC Centre of Excellence for Climate System Science

Session 3.5 – February 7, 2018, 1145-1200

New Caledonia is among the largest and most populated islands in the tropical South Pacific. As is typical for South Pacific islands, it is regularly subjected to short-lived periods of extreme rainfall. These events are due to an interaction between large scale variability and complex topography, as well as local atmospheric circulations. It is important that high resolution atmospheric models, used in weather prediction services and regional climate studies, are able to capture the physical processes leading to extreme rainfall, although this is not always the case.

We investigate three models' ability to replicate extreme precipitation over New Caledonia, by undertaking a case study of an event which occurred on 21 November 2016. This event created major flooding in New Caledonia, leading to loss of life. The models chosen are the Weather Research and Forecasting model (WRF), the Application of Research to Operations at Mesoscale (AROME, Météo- France) and the regional version of the Australian Community Climate and Earth System Simulator (ACCESS-R, Bureau of Meteorology). Each model is able to simulate observed orographic rainfall, as long as topography is reasonably represented. However, there is significantly less modelled rainfall produced due to organised processes. Organisation within the models is shown to be highly sensitive to initial atmospheric conditions and sea surface temperatures, which highlights the stochastic nature of these events and the challenge to accurately predict them.

173

Recent changes in mean and extreme temperature and rainfall in the western Pacific McGree, Simon1, Herold, Nicholas2, Schreider, Sergei1, Kuleshov, Yuriy1, Alexander, Lisa2

Presenting author’s e-mail: [email protected]

1School of Science, RMIT University, GPO Box 2476, Melbourne, VIC 3001, Australia 2Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, NSW, 2052, Australia.

Session 3.5 – February 7, 2018, 1200-1215

The character and severity of impacts from climate extremes depend not only on the extremes themselves but also on exposure and vulnerability. While the western Pacific Islands vary in their geography, climate, culture and stage of economic development, they have many common characteristics which highlight their exposure and vulnerability, particularly as it relates to sustainable development and climatic change. As such it is imperative that a sound understanding of past and likely future changes in western Pacific climate be attained, to stand the best chance of sustaining life on these islands in the coming century and beyond.

We describe the development of daily homogenous rainfall and temperature datasets and associated annual and seasonal analyses of these data. Mean warming trends are spatially homogenous and dominate across the region with annual mean warming 0.14 °C per decade over the last 65 years. Trends in total rainfall are spatially heterogeneous and largely non-significant over the same period. Only in the subtropics is there a drying trend, consistent with broader trends seen in parts of southern and eastern Australia.

We have also analysed a suite of indices defining a range of climate extremes which have been developed by the World Meteorological Organization Expert Team on Sector-Specific Climate Indices. In this way the current research fits into an existing global framework, building on an international effort to improve understanding of extreme climate variability and trends. Homogeneous warming exists in station-level temperature extremes for over 30 stations. In some cases the frequency of warm nights/days has increased more than four fold over the last 65 years, which in contrast the number of cool nights/day has decreased dramatically, with these becoming rare in the most recent period.

174

On the relationship between Indian Ocean Sea Surface Temperature Variability and Tropical Cyclogenesis in the Southwest Pacific Magee, Andrew1, Verdon-Kidd, Danielle1

Presenting author’s e-mail: [email protected]

1Environmental and Climate Change Research Group (ECCRG), School of Environmental and Life Sciences, Faculty of Science, University of Newcastle, Australia

Session 3.5 – February 7, 2018, 1215-1230

In the Southwest Pacific (SWP) tropical cyclones (TCs) account for 76% of the regions natural disasters and have substantial economic, physical and environmental impacts on people and places. Therefore, information is needed to better understand when and where TCs are likely to occur, as this can aid in preparedness and planning. While there is a well-established relationship between Pacific Ocean sea surface temperature (SST) variability and tropical cyclogenesis (TC genesis) in the SWP, it does not fully explain the historical spatial and temporal variability observed. Therefore, this study aims to look beyond the Pacific and establish a new relationship between Indian Ocean SST variability and SWP TC genesis. This is achieved by statistically relating indices of Indian Ocean SST variability to SWP TC genesis positions. The physical mechanisms driving these observed relationships are then established by studying changes in the environmental conditions conducive to TC genesis. This analysis shows that Indian Ocean SST variability significantly modulates the clustering of SWP TC genesis, where warmer (cooler) SSTs in the eastern and western regions of the Indian Ocean result in a statistically significant north/east (south/west) migration of TC genesis by up to 950km. Importantly, this relationship is shown to be consistent when the El Niño/Southern Oscillation (ENSO, the dominant Pacific mode) is in an inactive phase (ENSO Neutral). Favourable TC genesis parameters including warm SSTs, increased relative humidity, anomalously negative 700hPa vorticity, anomalously negative and low absolute 200hPa-850hPa vertical wind shear account for the observed shift in clustering. Further, we show that the combined effect of ENSO/Indian Ocean SST variability results in varying risk profiles for island nations of the region, with the two climate modes either enhancing or suppressing individual impacts. Significantly, the findings from this study provide an opportunity for meteorological agencies to improve seasonal SWP TC outlooks.

175

Impact of low-frequency oscillations on rainfall in French Polynesia Laurent, Victoire1

Presenting author’s e-mail: [email protected]

1Météo-France, Tahiti, French Polynesia

Session 3.5 – February 7, 2018, 1230-1245

From series of precipitation, this study describes the impact of low frequency oscillations on the Polynesian climate. Several modes are involved, from interdecadal to intraseasonal time steps. The Empirical Orthogonal Functions (EOFs) and time spectral analysis are used to characterize climate pattern of rainfall in French Polynesia and its variability. The results are based on the rainfall observed on the archipelagos of Marquesas, Tuamotu, Society and Austral. In Marquesas, the seasonal cycle is significant and strongly affected by phases of ENSO (El Niño Southern Oscillation). The 30-60 days peaks related MJO (Madden and Julian Oscillation) in the rainfall spectra show a preference for positive ENSO. It is also on that archipelago where the IPO (Interdecadal Pacific Oscillation) signal has been strongly detected. Northern Tuamotu is influenced at the same time by the Marquesas and the Society climate. But the analysis didn’t show significant signal over center and south Tuamotu. On the islands of Society the seasonal cycle dominates. Only the 14-30 days peaks related variability of SPCZ (South Pacific Convergence Zone) and the 30-60 days peaks bring a small fluctuation. Finally, in Austral islands the interannual variability mainly related ENSO and intraseasonal variability linked with subtropical anticyclones modulations dominate the seasonal cycle in the same way. The SAM (Southern Annular Mode) 5-21 days peaks is explored in order to define its link with disturbances of cold season that affects the southern coasts of the Southern islands. A key component of the ENSO impact in French Polynesia, in cold phase like in warm phase, would be the presence or not of the Inter Tropical Convergence Zone (ITCZ) in the south of the equator, close to Marquesas. Even in cold phase (Niña), the formation of the ITCZ in the South of the equator induces an El Niño-like limited to French Polynesia.

176

Effect of ENSO and IPO on rainfall in the Pacific Islands Weir, Tony1, Kumar, Ravind2

Presenting author’s e-mail: [email protected]

1Fenner School of Environment and Society, Australian National University, Canberra ACT 2Fiji Meteorological Service, Nadi, Fiji

Session 3.5 – February 7, 2018, 1245-1300

We examine the effect of the El Nino Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO) on rainfall in the Pacific Islands using records from the few stations in Vanuatu, Fiji and Cook Islands that have records extending over 100 years, and compare the results to those from Australia. Our analysis uses correlations between annual averages of SOI and rainfall, calculated over ‘ENSO years’ (i.e. May-April), as the impacts of ENSO are most marked in the southern summer. We focus especially on those years which have marked El Nino or La Nina events.

Our results confirm that there is a significant influence of ENSO on rainfall in these islands, and that the correlations may depend in differing ways on the state of the IPO. These effects relate to the movement of the South Pacific Convergence Zone, which is subject to independent shifts in El Nino events and with IPO, and therefore differ from those in Australia.

177

3.6 Modelling, prediction and projections of climate variability and change Preparing ACCESS for CMIP6 Marsland, Simon1, Bi, Dave1, Bodman, Roger2, Chamberlain, Matt3, Karoly, David2, Dix, Martin1, Dobrohotoff, Peter1, Fiedler, Russell3, Rashid, Harun1, Law, Rachel1, Sullivan, Arnold1, Ziehn, Tilo1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, VIC, Australia 2University of Melbourne, VIC, Australia 3CSIRO Oceans and Atmosphere, TAS, Australia

Session 3.6 – February 6, 2018, 0930-0945

“Preparing ACCESS for CMIP6” is an underpinning project of the National Environmental Science Programme (NESP) Earth System and Climate Change (ESCC) Hub. The Australian Community Climate and Earth System Simulator (ACCESS) is Australia’s global climate model, which provided climate simulations for IPCC’s Fifth Assessment. Given its importance to Australia’s climate preparedness and resilience, ACCESS needs to be an internationally benchmarked, world-class global climate modelling capability that is significantly more accurate than other global climate models for the Australasian and Southern Hemisphere region. Participation in the World Climate Research Programme Climate Model Intercomparison Project (CMIP) provides this benchmarking. It also supports Australia’s effective management of climate risks and opportunities, and engagement with future climate assessments. This project addresses these outcomes by preparing the current ACCESS model for participation in the CMIP (CMIP6) to benchmark ACCESS’s performance and suitability for application across the NESP ESCC Hub. An overview is given of the ACCESS model version, status, plans and timelines for the CMIP6 submission.

178

Earth System Model development under the Deep South National Science Challenge Morgenstern, Olaf1, Williams, Mike1, Behrens, Erik1, Bowen, Melissa2, Dennison, Fraser1, Smith, Inga3, Langhorne, Pat3, Varma, Vidya1, McDonald, Adrian4, Williams, Jonny1

Presenting author’s e-mail: [email protected]

1NIWA, Wellington, New Zealand 2Dept. of Physics, U. Auckland, New Zealand 3Dept. of Physics, U. Otago, Dunedin, New Zealand 4Dept. of Physics and Astronomy, U. Canterbury, Christchurch, New Zealand

Session 3.6 – February 6, 2018, 0945-1000

Climate models used for the 5th Assessment Report of the Intergovernmental Panel in Climate Change are characterized by some pervasive problems specific to southern high latitudes. These problems affect projections of climate change derived from these model simulations. Amongst them are a common failure to adequately simulate sea ice; difficulties with simulating Antarctic bottom water formation, a key component of the global ocean circulation; widespread underestimation of cloud cover over the Southern Ocean leading to large errors in radiation fluxes; and for those models that use interactive ozone, large inaccuracies with the simulation of the ozone layer and particularly the Antarctic ozone hole. The problems are caused by a variety of factors including incomplete understanding of the underlying physics, difficulties with representing small-scale processes in coarse- resolution climate models, and the inability to devote sufficient computational resources to those processes. The difficulties are compounded by the coupled nature of the system, whereby problems with the simulation of one aspect of the climate system have implications for the simulation of others.

The Deep South National Science Challenge is the New Zealand Government’s response to these issues. Under the Challenge, the NZ science community is charged with developing a “New Zealand Earth System Model” that improves on this situation. Joining forces with the UK Met Office and its partners, under the Challenge we are conducting research towards improving the simulation of clouds in the model, we are working on adding new physics on sea ice formation and loss, we are experimenting with new ways to better capture Antarctic bottom water formation, and we are advancing the formulation of stratospheric ozone chemistry. Several projects in this domain comprise both an observational and a model development component, reflecting that we aim to base our model development on recent, novel observations of high-latitude physical processes.

179

Preliminary results of the ACCESS-CM2 Pre-industrial Spin-up for CMIP6 Experiments Bi, Daohua1, Dix, Martin1, Dobrohotoff, Peter1, Sullivan, Arnold1, Marsland, Simon1, Rashid, Harun1, O’Farrell, Siobhan1, Yan, Hailin2, Bodman, Roger3

Presenting author’s e-mail: [email protected]

1Climate Science Centre, CSIRO Ocean and Atmosphere, Aspendale, Australia 2Bueau of Meteorology, Melbourne, Australia 3University of Melbourne, Parkville, Australia

Session 3.6 – February 6, 2018, 1000-1015

ACCESS-CM2, a new generation of the ACCESS coupled model, has been developed at the Climate Science Centre, CSIRO Ocean and Atmosphere for the purpose of global climate and climate change research and applications. It contains the UK Met Office atmospheric model (UM10.6/GA7.1) coupled to CSIRO land surface model CABLE2, the GFDL ocean model (MOM5), the Los Alamos sea ice model (CICE5.1), and a numerical coupler (OASIS3-MCT). The CMIP6 version of this coupled system is configured with horizontal resolution of N96 UM atmosphere (with land surface model Jules/CABLE) and 1-degree ocean-sea ice. A multi-century spin-up simulation with pre-industrial forcing has been conducted, and the result is presented in this talk to assess the overall performance of ACCESS-CM2 in simulating the global pre-industrial climate and climate variability.

180

Selecting a climate model subset to optimise key ensemble properties Herger, Nadja1, Abramowitz, Gab1, Knutti, Reto2,4, Angélil, Oliver1, Lehmann, Karsten3, Sanderson, Benjamin M.4

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2ETH Zurich, Zurich, Switzerland 3Satalia, Berlin, Germany 4National Center for Atmospheric Research, Colorado, USA

Session 3.6 – February 6, 2018, 1015-1030

Large multi-model ensembles, whose composition and size are often arbitrarily determined, are commonly used for climate projections. They are an indispensable tool to learn about initial condition, boundary condition, parameter as well as structural uncertainties. Because of a lack of agreed-on alternatives, the equally weighted multi-model ensemble mean is often used as a best estimate. However, due to the presence of duplicated code and shared development history, different climate model simulations cannot necessarily be regarded to be truly independent and the “one-model, one- vote” paradigm seems inappropriate. Here, we present an efficient and versatile method that finds a CMIP5 model subset which optimises certain key properties from the full ensemble. We apply it to both mean state climate variables by minimising regional climatology biases and to climate extremes by reducing biases in the shape of temperature and precipitation distributions. This process is essentially a calibration exercise, where the cost function being optimised, the metric, choice of variables and region need to be carefully tailored based on the use-case of interest. Calibrating on one application does not guarantee skill in another one.

181

What climate sensitivity measure is most useful for projections? Grose, Michael1, Gregory, Jonathan2, Colman, Rob3, Andrews, Timothy4

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, TAS, Australia 2University of Reading, Reading, UK 3Bureau of Meteorology, VIC, Australia 4UK MetOffice, Exeter, UK

Session 3.6 – February 6, 2018, 1100-1115

Indices of climate sensitivity attempt to quantify the magnitude of climate response for a given forcing, so could potentially be useful for quantifying and understanding ranges of change in climate projections from different models. Temperature change for the 21st Century under the representative concentration pathways (RCPs) represents climate change not at equilibrium, so it was previously assumed that transient climate sensitivity (TCR) or transient climate response at 140 years (T140) would explain more variance between climate models than equilibrium climate sensitivity (ECS). Here we look at projections of global and regional temperature under the RCPs, and examine the variance between models that these sensitivity indices explain. For change in global mean surface air temperature (∆GMSAT) from pre-industrial, indices of transient response do indeed explain more of the spread in models than ECS, until ECS is comparable near 2100. This is perhaps expected given how the indices are estimated. However, there is a more complex situation for projections over shorter sub-periods within pre-industrial and 2100. Trends over 50 or 100 years correlate more closely with transient indices in historical periods, but ECS actually explains more variance between models than TCR or T140 in future projections to 2100 (e.g. 1986-2005 to 2080-2099), which is perhaps less expected given the indices. This result is consistent across RCPs, suggesting it is not a result of the balance between greenhouse gas aerosol forcing. It is not clear why these relationships change through time, and it appears to depend on the rate of change and the duration since forced change has commenced. More work and possibly the analysis of different model simulations are needed to understand and quantify the specific reasons for these relationships. We also find that the ability of sensitivity indices to describe the range of temperature projections of the 21st Century also varies considerably in space, with all indices failing to explain more than two thirds of the variance in many regions.

182

Does ENSO change under anthropogenic forcing? Maher, Nicola1,2, Matei, Daniela1, Marotzke, Jochem1

Presenting author’s e-mail: [email protected]

1Max-Planck Institude for Meteorology, Hamburg, Germany 2Alexander von Humboldt Foundation, Germany

Session 3.6 – February 6, 2018, 1115-1130

There is little consensus in the literature as to how the El Niño Southern Oscillation (ENSO) may change under future greenhouse gas warming, with climate models showing a large range of future projections. This project utilises the large ensemble of the MPI-ESM-LR climate model to address the range of internal variability in the system and determine whether ENSO changes under a variety of anthropogenic warming scenarios.

The large ensemble allows us to quantify the ENSO pattern and how it changes over time. Here, an EOF analysis is applied over the ensemble dimension. We find that the pattern can change under strong warming scenarios. The ensemble also allows the identification of the influence of internal variations on future projections. Here, the variability is large and may explain why projections from different models have such a large range and show little consensus. We also show that changes in ENSO variability over the last 25 years are well within internal variations produced by the model. Finally, we find that the precipitation patterns during ENSO events change under anthropogenic forcing, which could have wide ranging impacts.

183

On the choice of ensemble mean for estimating the forced signal in the presence of natural variability Frankcombe, Leela1, England, Matthew1, Kajtar, Jules2, Mann, Michael3, Steinman, Byron4

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2University of Exeter, Exeter, UK 3Pennsylvania State University, Pennsylvania, USA 4University of Minnesota Duluth, Minnesota, USA

Session 3.6 – February 6, 2018, 1130-1145

In this presentation we use synthetic data to examine various options for the calculation of the forced signal in climate model simulations, and the impact these choices have on the estimates of internal variability. We find that an ensemble mean of runs from a single climate model (a single model ensemble mean, or SMEM) provides a good estimate of the true forced signal even for models with very few ensemble members. When applied to models with only a single ensemble member, however, the SMEM is in general out-performed by the scaled ensemble mean from all available climate model simulations (the multi-model ensemble mean, or MMEM). We therefore recommend that a scaled MMEM is used as an estimate of the forced signal for observations, rather than estimates from single models. The MMEM method does lead to increasing errors further into the future, as the different climate sensitivities of the models causes their trajectories to diverge. We therefore apply the SMEM method to those few models with a sufficient number of ensemble members to estimate the change in the amplitude of internal variability under a future forcing scenario. We find that on average the SAT variability decreases at higher latitudes, particularly over the ocean along the sea ice margins, while variability in precipitation increases on average, particularly at high latitudes.

184

On the Improved Turbulent Kinetic Energy Spectrum in ACCESS via Stochastic Backscatter Injection Dobrohotoff, Peter1, Kitsios, Vassili2, Frederiksen, Jorgen1, Dix, Martin1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Aspendale, VIC, Australia 2CSIRO Oceans and Atmosphere, Hobart, TAS, Australia

Session 3.6 – February 6, 2018, 1145-1200

We have demonstrated that the appropriate injection of stochastic backscatter in the Australian Community Climate and Earth System Simulator (ACCESS) can improve the realism of the turbulent kinetic energy (TKE) spectrum. By preferentially injecting energy over a suitable range of high wavenumbers, we have produced more realistic TKE spectra within the inertial wavenumber range of the atmosphere. This in effect mitigates the artificial numerical dissipation associated with the interpolation used in semi-Lagrangian time stepping and other physical parameterisations. We have also demonstrated the "tail wagging the dog" effect, where injecting stochastic backscatter at high wavenumbers results in lower kinetic energy at low wavenumbers. This is consistent with Fjørtoft's theorem. We present the impact that such an injection into the small scales has on the large-scale flow, in particular the structure of the hemispheric jets. Previous studies have shown that more physically realistic TKE spectra produce improved predictability and a more accurate representation of large-scale phenomena.

185

Conceptual understanding of the large-scale hydrological cycle with a globally resolved energy balance model Stassen, Christian1, Dommenget, Dietmar1

Presenting author’s e-mail: [email protected]

1Monash University, ARC COE for Climate System Science, VIC, Australia

Session 3.6 – February 6, 2018, 1200-1215

Much of our understanding about the large scale hydrological cycle and how it may change under global warming we gain from coupled general circulation models (CGCMs). They are the most sophisticated and complex tools available. Nevertheless, they do have substantial biases and uncertainties that limit their skills. Furthermore, it is difficult to understand the interactions leading to the large-scale hydrological cycle, the origin of uncertainties and its change under global warming based on CGCMs due to the high complexity of these models.

We will illustrate that the large-scale hydrological cycle can be simulated in a Globally Resolved Energy Balance (GREB) with similar skill as in CGCM simulations. We further, show how to mimic the climate mean state of different CMIP models using GREB. The results show that the GREB model is able to reproduce simulated biases in the hydrological cycle in the annual mean and seasonal cycle of CMIP models. By decomposing these biases in the CMIP models into different contributions we illustrate the origin of large-scale hydrological cycle problems in CMIP models.

186

3.7 Decadal climate prediction session The CAFE EnKF system for coupled data assimilation and forecast initialisation in the seasonal to multi-year space Sandery, Paul1, O’Kane, Terence2, Sakov, Pavel1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, TAS, Australia 2CSIRO Marine and Atmospheric Research, TAS, Australia

Session 3.7 – February 5, 2018, 1100-1115

The Climate Analysis Forecast Ensemble (CAFE) EnKF system runs a 96 member ensemble of the GFDL coupled model CM2.1 on a 30 day sequential cycle. It carries out coupled data assimilation using covariances between the atmospheric and ocean models to analyse, initialise and forecast the coupled state. The system carries out asynchronous data assimilation where the model is compared to observations each day within the cycle and this information is used to calculate coupled analysis increments and verification statistics. An EnKF SST bias detection and correction scheme is included to reduce the negative impact SST bias has on other variables in the multivariate system. The system assimilates all ocean observations typically available for ocean forecasting, RADS altimetry, SST from NavOceano, AMSR-E, AMSR-2, Pathfinder, VIIRS and Himaware-8, surface salinity from Aquarius and SMOS and in-situ temperature and salinity from Argo, CTD, PIRATA, TAO, CARS31 and MMT. A coupled reanalysis is performed from 2002 up until present. Results show that the CAFE EnKF system has meaningful spread-error relationships and constrains both the atmosphere and ocean to modes relevant for multi-year climate forecasting. The behaviour of CAFE EnKF is in agreement with theoretical studies using the Lorenz 3-equation coupled model that illustrate the EnKF has the ability to constrain the relevant longer time-scale modes of predicability in the atmosphere and ocean through assimilating ocean observations only.

187

Decadal climate predictability in the southern Indian Ocean captured by SINTEX- F using a simple SST-nudging scheme Morioka, Yushi1, Doi, Takeshi1, Behera, Kumar Swadhin1

Presenting author’s e-mail: [email protected]

1Application Laboratory, JAMSTEC, Yokohama, Japan

Session 3.7 – February 5, 2018, 1115-1130

Decadal climate variability in the southern Indian Ocean has great influences on southern African climate through modulation of atmospheric circulation. It exhibits a clear bi-decadal (18-20 yr) variation and the rainfall increase over southern Africa on decadal timescale is strongly associated with warm sea surface temperature (SST) and high sea level pressure (SLP) anomalies in the southern Indian Ocean. Although several studies attempted to understand physical processes leading to predictability of the decadal climate variability, the internally generated variability independent from external atmospheric forcing remains poorly understood. This study investigates predictability of the decadal climate variability in the southern Indian Ocean using a coupled general circulation model, called SINTEX-F. The ensemble members of the decadal retrospective forecasts were initialized with a simple SST-nudging scheme in which the model SST is strongly relaxed to the observation by adding negative feedback to the surface heat flux. It is found that the observed positive and negative peaks during late 1990s and late 2000s are well reproduced in the re-forecasts initiated from March 1st in 1994 and 1999, respectively. The re-forecasts initiated from March 1st in 1994 successfully capture warm SST and high SLP anomalies propagating from the South Atlantic to the southern Indian Ocean. Also, some other re-forecasts initiated from March 1st in 1999 skilfully predict a distinct phase change from a positive to negative peak. These results suggest that the SST-nudging initialization, though a simple scheme, has the essence to capture the predictability of the internally generated decadal climate variability in the southern Indian Ocean.

188

Model under-representation of decadal Pacific wind trends due to tropical Atlantic biases McGregor, Shayne1,2, Stuecker, Malte F.3,4, Kajtar, Jules B.5, England, Matthew H.2,6, Collins, Mat5

Presenting author’s e-mail: [email protected]

1School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria, Australia. 2ARC Centre of Excellence for Climate System Science, Australia 3Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA. 4Cooperative Programs for the Advancement of Earth System Science (CPAESS), University Corporation for Atmospheric Research (UCAR), Boulder, Colorado, USA. 5College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK 6Climate Change Research Centre, University of New South Wales, Sydney, Australia

Session 3.7 – February 5, 2018, 1130-1145

Pacific Trade Winds displayed unprecedented strengthening in recent decades. This Trade Wind acceleration has been associated with sea surface cooling in the eastern Pacific, rapid sea-level rise in the western Pacific, the early 21st Century slowdown in global surface warming, amongst a host of other substantial impacts. State of the art climate models produce decadal wind trends that are roughly half the magnitude of this observed trend, suggesting that the models underestimate internal variability in the Pacific Ocean and therefore impacting the variability of global mean surface temperatures. Recent progress in determining the cause of this Pacific Trade Wind acceleration has identified inter-basin links, highlighting an increasingly prominent connection between the Pacific and Atlantic basins. However, the details of why models appear to drastically underestimate the magnitude of Pacific decadal trends remain unknown. Here we analyze a series of targeted climate model experiments to show that when the recent Atlantic sea surface temperature warming trend is combined with the typical climatology bias in climate models, the Pacific Trade Wind acceleration and eastern Pacific Ocean cooling remains dramatically underestimated. This result highlights the importance of the climatological background states role in correctly representing trans-basin climate variability, and also the potential benefits of flux-corrected methods.

189

Dynamical downscaling of CanSIPS climate forecasts over North America Merryfield, William1

Presenting author’s e-mail: [email protected]

1Canadian Centre for Climate Modelling and Analysis, Victoria, Canada

Session 3.7 – February 5, 2018, 1145-1200

The Meteorological Service of Canada’s operational seasonal forecasts are provided by the Canadian Seasonal to Interannual Prediction System (CanSIPS). CanSIPS is a multi-model ensemble consisting currently of two global climate models, CanCM3 and CanCM4, having relatively coarse horizontal spatial resolutions of ~250 km in the extratropics. This has motivated the exploration of dynamical downscaling over a limited-area domain as a means for enhancing spatial detail and representing orographic influences that are absent in the global forecasts. This presentation will describe methodologies and results of this effort, including evidence for added value in a set of hindcasts downscaled to 25 km resolution in the CORDEX North America domain using the CanRCM4 regional climate model.

190

The CSIRO Climate Analysis Forecast Ensemble system O’Kane, Terence1, Sandery, Paul2, Sakov, Pavel2, Chamberlain, Matt1

Presenting author’s e-mail: [email protected]

1CSIRO, Hobart, TAS, Australia 2Bureau of Meteorology, Docklands, VIC, Australia

Session 3.7 – February 5, 2018, 1200-1215

CSIRO have recently commenced research and development of a Climate Analysis Forecast Ensemble (CAFÉ) system to investigate predictability of the ocean-atmosphere-ice-biogeochemical state at multi-year time scales. The approach is to develop a probabilistic forecast system for timescales beyond a season, based on generalising theoretical concepts from modern weather prediction whose mathematical principles are common to the problem of prediction in general high dimensional multi- scale systems. A model ensemble is a set of forecast runs that differ from a control simulation by the introduction of small perturbations into each ensemble member forecast. An initialised forecast will eventually depart from the true system as errors in the forecast grow. The rate at which the forecast diverges from the truth is a key indicator of transitions between climate regimes – e.g. periods of flood or drought. The requirement of a successful ensemble prediction system is to track and slow the growth of error modes ensuring more skillful forecasts. This is a mathematically complex task but one that is now potentially possible given the expansion of ocean observing systems, more realistic climate models and new theoretical advances. In this talk we describe the current system (CAFEv1) and next generation data assimilation and ensemble prediction components (CAFEv2). We contrast results from ensembles of general circulation models with those from idealized paradigm models discussing the theoretical underpinnings of the system and future directions.

191

Initialized decadal prediction for transition to positive phase of the Interdecadal Pacific Oscillation and resumption of larger rates of global warming Meehl, Gerald A.1, Hu, Aixue1, Teng, Haiyan1

Presenting author’s e-mail: [email protected]

1National Center for Atmospheric Research, Colorado, U.S.A.

Session 3.7 – February 5, 2018, 1215-1230

The negative phase of the Interdecadal Pacific Oscillation (IPO), a dominant mode of multi-decadal variability of sea surface temperatures (SSTs) in the Pacific, contributed to the reduced rate of global surface temperature warming in the early 2000s. A proposed mechanism for IPO multidecadal variability indicates that the relative magnitude of decadal timescale upper ocean heat content in the off-equatorial western tropical Pacific could provide conditions for an interannual El Niño/Southern Oscillation (ENSO) event to trigger a transition of tropical Pacific SSTs to the opposite IPO phase. Evidence is presented from a set of initialized hindcasts with CCSM4 to show this role for El Niño in the 1970s transition to positive IPO, and for La Niña in the late 1990s transition to negative IPO. A decadal prediction initialized in 2013 shows that the Niño3.4 SSTs qualitatively tracked the observations through 2015. The year 3-7 average prediction (2015-2019) from the 2013 initial state shows a transition to the positive phase of the IPO from the previous negative phase, and a resumption of larger rates of global warming over the 2013-2022 period consistent with a predicted positive IPO phase.

192

Assessing the predictability of ENSO using historical climate forecasts from the CAFE system Matear, Richard1, O’Kane, Terence1, Chamberlain, Matt1, Stevens, Lauren1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Australia

Session 3.7 – February 5, 2018, 1445-1500

A climate forecast dataset from the 2005 to 2016 period has been generated using the Climate Analysis, Forecast, Ensemble (CAFE) system. We first use this dataset to assess the potential predictability of ENSO. Second, we evaluate the ability of our forecast ensemble to predict El Nino and La Nina events. We show that initialising the climate state with ocean observations improves our forecast skill. Finally, we discuss the future improvements of the CAFE system to design to help realise potential predictability of ENSO.

193

On the dynamics of extreme rainfall in Tasmania Tozer, Carly1, Risbey, James1, O’Kane, Terence1, Monselesan, Didier1, Pook, Mike1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans & Atmosphere, Hobart, Australia

Session 3.7 – February 5, 2018, 1500-1515

Although small in size, the island State of Tasmania is Australia’s largest producer of renewable electricity from hydropower. The hydropower storages are located in the west of the State and given the sensitivity of the industry to rainfall (and subsequently streamflow) variability and extremes, it follows that skilful climate forecasts may assist in water resources and hydropower planning. The skill of rainfall forecasts lies in the ability of forecast models to simulate the climate processes that influence the rainfall variability in the region at relevant timescales. Climate in western Tasmania is unique from both eastern Tasmania and indeed the rest of Australia, due to local topographical influences and its location in the path of the prevailing high-latitude westerly winds. Beyond this knowledge there is a limited understanding of the synoptic and dynamic processes influencing rainfall variability and extremes. This study addresses this gap through characterisation of rainfall extremes in the region and the construction of atmospheric flow composites around these extreme events. Data from both a reanalysis product and a coupled climate model simulation are used in the analysis, which will ultimately help to evaluate and interpret forecast models.

194

Diagnosis of the extent of balance in the JRA-55 reanalysis via a normal mode function expansion Kitsios, Vassili1, O’Kane, Terence1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, TAS, Australia

Session 3.7 – February 5, 2018, 1515-1530

In the context of multi-year simulations of the atmosphere and ocean, the goal of data assimilation is to both shift the simulations toward physical observations, and attempt to achieve a balanced state. Normal mode functions (NMFs) can be used to determine to what extent a given flow field is balanced or unbalanced. We demonstrate this with application to the Japanese 55-year Reanalysis (JRA-55).

Daily flow fields of the reanalysis are decomposed into a series of NMFs of varying vertical and horizontal scale. The NMFs are the eigensolutions of a primitive equation model on a sphere. For a specified static stability profile the NMFs simultaneously represent the fluctuations in the mass and velocity fields. Note, in comparison spherical harmonics are the eigenvectors of the global barotropic vorticity equation and hence represent a simplified physical view of the atmosphere. Each NMF is characterised by a zonal wavenumber, meridional wavenumber, and vertical mode number. From the properties of the eigenvectors, the NMFs are additionally classified as being either balanced modes, westerly travelling inertial gravity waves, or easterly travelling inertial gravity waves. The balanced modes are slower evolving and potentially predictable. The inertial gravity modes have much faster time scales and dominate the prediction error growth. The NMF calculations are performed using the MODES code developed at the National Center for Atmospheric Research by Žagar and co-workers.

We diagnose to what extent each flow field in the JRA-55 reanalysis is balanced, by comparing the contribution of the balanced and unbalanced modes to the time varying kinetic energy spectra as a function of horizontal and vertical scale. In future work the NMFs will be used to filter out the inertial gravity waves in the initial conditions of the CSIRO Climate Analysis Forecast Ensemble (CAFE) decadal prediction system, to ensure that each ensemble member starts from a balanced state.

195

Inter-basin sources for two-year predictability of the multi-year La Niña event in 2010-2012 Luo, Jing-Jia1, Hendon, Harry1, Alves, Oscar1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 3.7 – February 5, 2018, 1530-1545

Multi-year La Niña events often induce persistent cool and wet climate over global lands, altering and in some case mitigating regional climate warming impacts. The latest event lingered from mid-2010 to early 2012 and brought about intensive precipitation over many land regions of the world, particularly Australia. This resulted in a significant drop in global mean sea level despite the background upwards trend. This La Niña event is surprisingly predicted out to two years ahead in a few coupled models, even though the predictability of El Niño-Southern Oscillation during 2002-2014 has declined owing to weakened ocean-atmosphere interactions. However, the underlying mechanism for high predictability of this multi-year La Niña episode is still unclear. Experiments based on a climate model that demonstrates a successful two-year forecast of the La Niña support the hypothesis that warm sea surface temperature (SST) anomalies in the Atlantic and Indian Oceans act to intensify the easterly winds in the central equatorial Pacific and largely contribute to the occurrence and two-year predictability of the 2010-2012 La Niña. The results highlight the importance of increased Atlantic-Indian Ocean SSTs for the multi-year La Niña's predictability under global warming.

196

3.8 Regional climate projections and applications Developing the Conformal Cubic Atmospheric model for CORDEX regional climate projections Thatcher, Marcus1, Katzfey, Jack1, McGregor, John1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, VIC, Australia

Session 3.8 – February 6, 2018, 1430-1445

The Conformal Cubic Atmospheric Model (CCAM) is being developed by CSIRO to simulate the climate at regional scales and to produce regional climate projections. Since CCAM is based on a variable resolution, global cubic grid, it can be used to dynamically downscale atmospheric models without employing lateral boundary conditions. As a consequence, CCAM is flexible in how it can be used to produce regional climate projections such as those created for the CORDEX intercomparison project. This talk outlines the downscaling method used by CSIRO to produce regional projections for CORDEX and some of the implications of the CCAM approach. For CORDEX an ensemble of six CMIP5 Global Climate Models (GCMs) was downscaled to 50 km resolution from 1960 to 2100 (ACCESS1-0, CCSM4, CNRM-CM5, GFDL-CM3, MPI-ESM-LR and NorESM1-M), as well as downscaling ERA-Interim from 1980-2010. We bias-correct the mean and variance of the Sea Surface Temperatures predicted by the CMIP5 GCMs, which significantly improves the CCAM simulated present day-climate. The simulations included a prognostic aerosol model with direct and indirect effects, an original convection parameterisation, as well as the Australian community land-surface model, CABLE. Some of the predicted changes in Australian climate for temperature and rainfall will be discussed, together with some analysis of extreme rainfall. Future plans for CCAM’s CORDEX simulations will also be described, including a new 25 km resolution global simulation, the inclusion of basic predictions of surface hydrology, as well as exploring the benefits of using an atmosphere-ocean coupled version of CCAM.

197

Can bias correction of regional climate model lateral boundary conditions improve low-frequency rainfall variability? Rocheta, Eytan1, Evans, Jason2, Sharma, Ashish1

Presenting author’s e-mail: [email protected]

1School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW, Australia 2Climate Change Research Centre and ARC Centre of Excellence for Climate Extremes, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia

Session 3.8 – February 6, 2018, 1445-1500

Global climate model simulations inherently contain multiple biases which, when used as boundary conditions for regional climate models, have the potential to produce poor downscaled simulations. Removing these biases before downscaling can potentially improve regional climate change impact assessment. In particular, reducing the low-frequency variability biases in atmospheric variables as well as modelled rainfall is important for hydrological impact assessment, predominantly for the improved simulation of floods and droughts. The impact of this bias in the lateral boundary conditions driving the dynamical downscaling has not been explored before. Here the use of three approaches for correcting the lateral boundary biases including mean, variance, and modification of sample moments through the use of a Nested Bias Correction (NBC) method that corrects for low-frequency variability bias is investigated. These corrections are implemented at the 6-hourly time scale on the global climate model simulations, to drive a regional climate model over the Australian CORDEX domain. The results show that the most substantial improvement in low-frequency variability after bias correction is obtained from modifying the mean field, with smaller changes attributed to the variance. Explicitly modifying monthly and annual lag-1 autocorrelations through NBC does not substantially improve low-frequency variability attributes of simulated precipitation in the regional model over a simpler mean bias correction. These results raise questions about the nature of bias correction techniques that are required to successfully gain improvement in regional climate model simulations and show that more complicated techniques do not necessarily lead to more skillful simulation.

198

Future climate projections for the Australian Alps Ji, Fei1, Evans, Jason2, Di Luca, Alejandro2, Beyer, Kathleen1, Macadam, Ian1

Presenting author’s e-mail: [email protected]

1Office of Environment and Heritage, NSW, Australia 2University of New South Wales, NSW, Australia

Session 3.8 – February 6, 2018, 1500-1515

The Australian Alps is the highest mountain range in Australia. It comprises only about 0.16% of Australia in size, however, it is an important zone for ecosystem, biodiversity, energy generation and winter tourism. Observations have shown a general warming and a decrease of the snowpack over the Australian alpine region suggesting that climate changes related with the increase of greenhouse gases might be already occurring.

In this study, we used outputs of 12 historical and future Regional Climate Model (RCM) simulations (each with three time periods: 1990-2009, 2020-2039, and 2060-2079) from the NSW/ACT Regional Climate Modelling (NARCliM) project to investigate future changes in climate variables such as rainfall, natural snow cover and depth, temperature, snowmaking condition, and climate extremes.

The results show that there are substantial changes in regional climate for the Australian Alps, which will dramatically impact local natural systems. More assessments are required to quantify potential impacts of climate change and provide potential adaptation pathways.

199

Climate change projections and implications for decision making in the Wellington Region Pezza, Alex1, Pearce, Petra2, Tait, Andrew2, Mullan, Brett2

Presenting author’s e-mail: [email protected]

1Greater Wellington Regional Council & Victoria University of Wellington, Wellington, New Zealand 2National Institute of Water and Atmospheric Research, Wellington, New Zealand

Session 3.8 – February 6, 2018, 1515-1530

The effects of climate change are being felt all over the world. There is immense pressure for governments to act and deal with the problem before it is too late. In New Zealand, local government is at the frontline of the problem, having to deal with community and stakeholder’s expectations, and interpreting the Resource Management Act’s requirements on climate change consideration with limited support from central government. In August 2017, the Greater Wellington Regional Council released one of the most detailed climate change reports ever produced in New Zealand (commissioned by the council and written by NIWA). The report has been publicly released and is available online, after a launch event with mayors from all regional Territorial Authorities that aimed to promote climate leadership in the region. High resolution climate change projections for 2040 and 2090 are available for all Fifth Assessment RCPs for the southern end of the North Island. Projections are based on the dynamical downscaling using the HadRM3P regional climate model (27km resolution). This RCM is forced by sea surface temperature and sea ice from six AR5 models regarded as representative of the range of variability across New Zealand. A further statistical downscaling to the RCM to a final 5x5km horizontal resolution shows an emergence of topographic influence considerably better than any earlier attempts. Sole statistical downscaling of temperature and precipitation was also applied to all 41 AR5 models, allowing for a better understanding of the spread/uncertainty involved. The results highlight significant increases in drought risk in key farming areas east of the ranges (Wairarapa area), where the average year of the end of the century may look like the worst drought of the present, with a concomitant significant increase in heavy rainfall everywhere. Impacts on biodiversity, biosecurity, health, flood and Land Management are also discussed.

200

Impact of CMIP5 SST biases on the South Pacific Convergence Zone response to climate warming Cyril, Dutheil1, Bador, Margot2, Lengaigne, Matthieu3, Lefevre, Jérôme1, Jourdain, Nicolas4, Jullien, Swen5, Vialard Jérôme3, Peltier, Alexandre6, Menkes, Christophe1

Presenting author's e-mail: [email protected]

1IRD (Institut de Recherche pour le Développement )-Sorbonne Universités (UPMC, Université Paris 06)-CNRS-MNHN-IPSL, LOCEAN Laboratory, IRD Nouméa BP A5, 98848 Nouméa cedex, New Caledonia 2Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, School of BEES, University of New South Wales, Sydney, New South Wales, Australia 3LOCEAN-IPSL, Sorbonne Universités, UPMC, Université Paris 06, CNRS-IRD-MNHN, Paris, France. 4CNRS, LGGE, F-38402 Grenoble, France 5Ifremer, Univ. Brest, CNRS, IRD, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Plouzané, France 6Météo France, Nouvelle Calédonie

Session 3.8 – February 6, 2018, 1530-1545

The South Pacific convergence zone (SPCZ) is poorly represented in global climate models, with trademark biases such as the “double ITCZ” or related cold tongue biases. These biases may impact the SST anomalies between future and present climates. Such biases decrease also our confidence in climate change projections of precipitation for this region. In this study, we design a number of sensitivity experiments with the regional WRF atmospheric simulations to characterize how these biases modify the future SPCZ.

We first show that a 1°x1° regional configuration captures the SPCZ mean state and ENSO variability well over the 1980-2016 period. We then perform two climate change experiments. In the first experiment we classically add the RCP8.5, 2080-2100 CMIP5 multi-model seasonal boundary anomalies to the present conditions. The main impact is a significant rainfall increase of 65 % in the central and eastern equatorial Pacific. This result contrast with previous studies based on CMIP5 simulations that suggest a much weaker equatorial Pacific wettening (~35%). The rainfall response in the SPCZ is similar to what is found in CMIP5 with a drying of southeastern Pacific of ~15%. In the second experiment, we correct the projected CMIP5 SST anomalies with a « observation constraint » method based on Li et al (2016). This simulation yields a significant rainfall decrease in the southwestern pacific (~40%). Such drying is much stronger than the one deduced by Li et al. from CMIP5 outputs, and contrasts with the results of the first experiment. This strong drying in southwestern Pacific in this experiment can be tracked down to the correction of the projected CMIP5 SST anomalies biases. The process leading to that strong drying is dominated by dynamical responses where humidity transport to the SPCZ is reduced compared to the experiment with the orignal CMIP5 SST biases.

201

South Atlantic Ocean precipitation associated with extratropical cyclones Reboita, Michelle1, da Rocha, Rosmeri2, Ambrizzi, Tércio2

Presenting author’s e-mail: [email protected]

1Universidade Federal de Itajubá, Minas Gerais, Brazil 2Universidade de São Paulo, São Paulo, Brazil

Session 3.8 – February 6, 2018, 1645-1700

This study assesses the annual total precipitation over the South Atlantic Ocean (SAO) associated with the extratropical cyclones in the present (1997-2005) and future (2070-2098) climates. Cyclones were identified and tracked in the CFSR reanalysis and in a projection based on the Regional Climate Model (RegCM4) which was nested in the HadGEM2-ES global climate model outputs, considering future greenhouse gases scenarios (RCP8.5). For present climate, precipitation data were obtained from the Global Precipitation Climatology Project (GPCP), which produces daily accumulations centred on 12:00 UTC in a horizontal grid with 1º x 1º. The methodology used to quantify the precipitation associated with the cyclones follows the steps: a) the position of all cyclones at 12:00 UTC during their entire lifecycle is selected; b) a radius is traced considering the centre of the cyclone (here we used 8 degrees) and c) for each position of the cyclone at 12:00 UTC, the precipitation in the area delimited by the radius is added. The cyclones in the CFSR reanalysis (and using GPCP precipitation) contribute to approximately 80% of the annual total precipitation in the sector around 40o S and 40o W. RegCM4 simulates a higher contribution of the cyclones to the precipitation (90%) and displaces the maximum of precipitation eastward compared with CFSR. In the future, the contribution of the cyclones for the annual total precipitation decreases more than 15% around 45o S and 35o W. This is the first work that evaluated the cyclones contribution to the precipitation over the SAO.

202

Integrating climate modelling into hydrological modelling at regional scale: a review of studies in Brazil Borges, Pablo de Amorim1, Chaffe, Pedro Luiz Borges1

Presenting author’s e-mail: [email protected]

1Universidade Federal de Santa Catarina, SC, Brazil

Session 3.8 – February 6, 2018, 1700-1715

Studies about the regional impacts of climate change on water resources have grown substantially in the last two decades worldwide; however, little is known about them in the Brazilian territory. The aim of this review is to identify how the scientific community has been dealing with the subject ‘integration of climate models into hydrological models’ in Brazil. The study is based on a meta- analysis of available peer-review literature. We propose a method for the evaluation of the degree of evidence of the impact studies, which is based on: i) theoretical foundation; ii) data used and iii) sophistication of the modelling procedure (climate modelling, regionalization and hydrological modelling). In addition, the most relevant conclusions of the collection of documents are synthesized according to the impacts. The assessment shows that the topic has grown substantially in this decade reaching 57 documents so far. The socioeconomic sectors under highest concern are drinking water supply and hydropower. The synthesis of the studies reveals likely impacts of climate change, such as: i) decreasing minimum streamflow in the Amazônica hydrographic region, and ii) changes in the seasonality in the Paraná, wherein the hydropower sector is the most affected. In terms of evidence level, the application of regionalization techniques and hydrological models is reasonably consistent with the current state-of-the-art, but the use of several climate model outputs (multi-model ensemble) is neglected in most of the studies. The results suggest a lack of technical support and infrastructure to access and assimilate climate data. At the same time, similar studies in the same region are limited, facts which compromise the confidence level of the summary messages. Nevertheless, the evaluation of the degree of evidence of the set of studies proved to be a valuable tool for guiding actions to improve the topic not only in Brazil but elsewhere.

203

Downscaling future climate scenarios to vineyard scale, examples from France and New Zealand Le Roux, Renan1, de Rességuier, Laure2, Sturman, Andrew3, Katurji, Marwan3, Zawar-Reza, Peyman3, Quénol, Hervé1, van Leeuwen, Cornelis2

1LETG, UMR 6554 CNRS, Université de Rennes 2, Place du Recteur Henri Le Moal, Rennes, France 2EGFV, Bordeaux Sciences Agro, INRA, Univ. Bordeaux, ISVV, F-33140 Villenave d’Ornon,France 3Centre for Atmospheric Research, University of Canterbury, Christchurch, New Zealand

Session 3.8 – February 6, 2018, 1715-1730

The IPCC has created climate scenarios to provide the basis for evaluating the impacts of climate change. All agricultural sectors should be concerned about such impacts, but particularly wine production, as temperature has a key role in grapevine development. Temperature variability can be significant at vineyard scale, and climate change models are not accurate enough to take into account such fine scale temperature variability. This study proposes a method for downscaling future climate scenarios to vineyard scale.

The study focuses on two vineyard areas, Saint-Émilion (France) and Marlborough (New Zealand). Eighteen weather stations recording temperature have been established in Marlborough. At Saint- Émilion, a network of 90 data loggers were used to collect air temperatures inside the vine canopy. These sets of measurements are used to create fine scale geostatistical models of temperature variation for the seasons 2013-2015 (March/October in France and September/April in New-Zealand). Temperature data for these periods are also available at lower resolution, from regional climate models for France (at 9 km resolution) and New Zealand (at 5 km resolution), while climate change model data (RCP scenarios) are also available at these scales.

For the selected growing seasons, temperature patterns at regional scale were identified by using a classification algorithm. Fine scale maps of daily average temperature were associated with categorized nodes, and then for each day of the future scenarios, the same regional patterns are identified and associated with the corresponding fine scale maps, creating fine scale maps for each day of the period 2005 – 2100 for scenarios. The results demonstrate, in agreement with the large- scale future scenarios, a rise of daily average temperature over both study sites. However, the spatial distribution of temperature is similar to that of the training period (2012-2015) for both the mid- (2031-2050) and longer term (2081-2100) predictions, whatever the scenario used.

204

Exploring the future change space for fire weather in southeast Australia Clarke, Hamish1,2, Evans, Jason3

Presenting author’s e-mail: [email protected]

1Centre for Environmental Risk Management of Bushfires, University of Wollongong, NSW, Australia 2Hawkesbury Institute for the Environment, Western Sydney University, NSW, Australia 3Climate Change Research Centre and ARC Centre of Excellence for Climate Extremes, University of New South Wales, NSW, Australia

Session 3.8 – February 6, 2018, 1730-1745

High resolution projections of climate change impacts on fire weather conditions in southeast Australia out to 2080 are presented. Fire weather is represented by the McArthur Forest Fire Danger Index (FFDI), calculated from an objectively designed regional climate model ensemble. Changes in annual cumulative FFDI vary widely, from -337 (-21%) to +657 (+24%) in coastal areas and -237 (-12%) to +1143 (+26%) in inland areas. A similar spread is projected in extreme FFDI values. In coastal regions, the number of prescribed burning days is projected to change from -11 to +10 in autumn and -10 to +3 in spring. Across the ensemble the most significant increases in fire weather and decreases in prescribed burn windows are projected to take place in spring. Partial bias correction of FFDI leads to similar projections but with a greater spread, particularly in extreme values. Partially bias corrected FFDI performs similarly to uncorrected FFDI compared to observed annual cumulative FFDI (ensemble root mean square error spans 540 to 1583 for uncorrected output and 695 to 1398 for corrected) but is generally worse for FFDI values above 50. This emphasizes the need to consider inter-variable relationships when bias-correcting for complex phenomena such as fire weather. There is considerable uncertainty in the future trajectory of fire weather in southeast Australia, including the potential for less prescribed burning days and substantially greater fire danger in spring. Selecting climate models on the basis of multiple criteria can lead to more informative projections and allow an explicit exploration of uncertainty.

205

3.9 Climate extremes in a warmer world – detection and attribution and implications of global warming thresholds Exploring the scalability of a suite of extreme indices in the context of the Paris low-warming targets Tebaldi, Claudia1, Armbruster, Alex2

Presenting author’s e-mail: [email protected]

1Climate and Global Dynamics Laboratory, NCAR, Boulder, CO, USA 2Georgetown University, Washington DC, USA

Session 3.9 – February 8, 2018, 1445-1500

Following the Paris agreements of 2015, which asserted the cogency of limiting warming well below 2 degrees to 1.5C above pre-industrial, NCAR performed ensemble simulations with the NCAR/DOE Community Earth System Model targeting specifically these low-warming levels. Besides their obvious direct relevance for impact research, these simulations, together with other large ensemble experiments previously performed with the same model under RCP4.5 and RCP8.5 offer the opportunity of testing the performance of well established emulation techniques, like pattern scaling. These techniques have been long tested and applied for traditional transient scenarios but have less frequently been applied to strongly mitigated, stabilized trajectories. Besides the scientific curiosity of testing the linear behaviour as a function of global average temperature of climate variables under these scenarios (an hypothesis at the basis of pattern scaling) results from these performance tests are of value to the wider community that might want to emulate low-warming scenarios using models other than NCAR’s.

In this talk I will present results from testing emulation techniques on a suite of 10 ETCCDI indices of extremes. The suite addresses the behaviour of daily minimum and maximum temperature and precipitation, synthesizing annual values of extremes. As to be expected, the performance of the emulation techniques varies among the indices and, for a given index, across space and across time, but in general the approximation works surprisingly well across many aspects of this validation exercise.

206

Evaluating simulated climate change in support of extreme weather event attribution Angélil, Oliver1, Donat, Markus1, Stone, Dáithí2

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2Laurence Berkeley National Lab, CA, U.S.A

Session 3.9 – February 8, 2018, 1500-1515

The field of event attribution aims to identify how the characteristics of climate extremes have changed due to anthropogenic climate change. One popular method to characterise the anthropogenic contribution to specific events involves calculating the probability change between two scenarios: climate model simulations forced with and without anthropogenic influences. Here we evaluate the long-term regional temperature and rainfall response to radiative forcing in five Atmosphere-only Global Climate Models (AGCMs), using two different approaches. We first make comparisons of changes during the recent historical period (1961-2012) between the AGCMs, reanalysis and observations. This analysis documents some regional differences in temporal changes of mean and extreme temperatures and precipitation, for example over the eastern US. Secondly, we investigate the response of regional temperatures to CO2 concentration changes. We find for most regions there is a linear relationship between CO2 concentrations and temperatures, and use this empirical relationship to extrapolate the climate under pre-industrial CO2 concentrations. These extrapolated ``natural'' temperatures are reasonably consistent over many regions with the simulations of a ``natural'' climate without anthropogenic influences. However, we also find considerable inconsistencies between these two estimates of natural climate in regions where early industrialisation took place, such as Europe and North America. These uncertainties can substantially bias attribution statements. We therefore highlight the need for more rigorous and more appropriate model evaluation, and to better account for those potential biases, to make responsible use of climate model simulations when estimating regional climate change and related occurrence probabilities of extreme weather and climate events.

207

Land use implications for climate extremes in low emission scenarios: Results from HAPPI-LAND Hirsch, Annette1, Guillod, Benoit P.1,2, Beyerle, Urs1, Boysen, Lena3, Brovkin, Victor3, Davin, Edouard L.1, Doelman, Jonathan C.4, Kim, Hyungjun J.5, Mitchell, Dann6, Nitta, Tomoko5, Seneviratne, Sonia I.1, Shiogama, Hideo7, Sparrow, Sarah8, Stehfest, Elke4, van Vuuren, Detlef P.4,9, Wilson, Simon10

Presenting author’s e-mail: [email protected]

1Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland 2Institute for Environmental Decisions, ETH Zurich, Switzerland 3The Land in the Earth System, Max Planck Institute for Meteorology, Hamburg, Germany 4PBL Netherlands Environmental Assessment Agency, Den Haag, the Netherlands. 5Institute of Industrial Science, University of Tokyo, Tokyo, Japan 6School of Geographical Sciences, University of Bristol, Bristol, UK 7Center for Global Environmental Research, National Inst. for Environmental Studies, Japan 8Oxford e-Research Centre (OeRC), University of Oxford, Oxford, UK 9Copernicus Institute for Sustainable Development, Utrecht University, The Netherlands 10Met Office Hadley Centre, Exeter, UK

Session 3.9 – February 8, 2018, 1515-1530

The impacts of land use and land management have been shown to have considerable influence on local climate, particularly in the context of extremes. With the recent commitment to limit global warming to well below 2˚C, emission reductions need to be ambitious and could involve major land- use change (LUC). These mitigation efforts to curb emissions growth involving substantial LUC include increasing terrestrial carbon sequestration through reforestation, transitioning away from fossil fuels towards bioenergy or changes in residue management to minimise carbon loss from soil disturbance. All of these activities have an impact on local climate through biophysical feedbacks associated with changes in albedo, roughness and evapotranspiration that accompany LUC. However, there is considerable uncertainty on how important these feedbacks are for half a degree of warming. Resolving this uncertainty was the motivation for HAPPI-LAND: the Half a degree Additional warming, Prognosis and Projected Impacts – LAND use scenario experiment, an extension to the existing HAPPI multi-model experiment. Using four Earth System Models we present the first multi-model results from HAPPI-LAND and demonstrate that the land-use scenario has a critical influence on regional climate extremes for low emission scenarios. In particular, regional changes in temperature extremes depend on whether mitigation efforts prioritise reforestation or the adoption of bioenergy crops. This highlights the need to consider how land use influences regional climate in the development of climate mitigation and adaptation pathways.

208

Changing frequency of flooding in Bangladesh: Is the wettest place on Earth getting wetter? Haustein, Karsten, Uhe, Peter F, Rimi, Ruksana H, Islam, AKM Saiful, Otto, Friederike E.L.

Session 3.9 – February 8, 2018, 1530-1545

Human influence on the Asian monsoon is exerted by two counteracting forces, (1) anthropogenic warming due to the influence of increasing Greenhouse Gas (GHG) emissions and (2) radiative cooling due to increased amounts of anthropogenic aerosols. GHG emissions tend to intensify the water cycle and increase monsoon precipitation, whereas aerosols are considered to have the opposite effect. Apart from the radiative cooling, aerosols may be responsible for meridional circulation anomalies on larger scales. Associated with it is tendency for a drier monsoon season that compensates a tendency towards wetter conditions in a purely GHG-driven scenario. On regional scales, aerosols weaken the thermal contrast between land and ocean which acts to inhibit the monsoon too.

As a result, neither observations nor model simulations that consider all human influences suggest clear changes in extreme precipitation at present. In reality, however, we are already “committed” to more rainfall extremes by virtue of the presence of aerosols. Eventually, pollution levels will come down, all the while GHG concentrations continue to rise due to further emissions. Thus we argue that it is crucial to assess the risk related to removing anthropogenic aerosols from the current world as opposed to standard experiments that use projected climate scenarios.

We present results from on analysis of extreme precipitation that led to the Bangladesh floods in summer 2016. Since the Meghalaya Hills are the major contributor to flood waters in Bangladesh, we focus on this particular region. In addition, we analyze the grid point representing Cherrapunji, also known to be the wettest place on Earth (situated on the southern flank of Meghalaya Hills), in an attempt to quantify the changing odds of future rainfall extremes in one of the most extreme environments in that respect. For our analysis, we use the well-established weather@home framework based on the HadRM3P model with 50km spatial resolution.

Our model results generally support the notion that rainfall extremes in Cherrapunji might have become more likely already. Mean rainfall is slightly lowered, but 21-day maximum rainfall under current “allforcing” conditions has occurred more often compared to the counterfactual world. While the 2016 rainfall event was not extreme, our results indicate that such flood-inducing rainfall is likely become more frequent without aerosols in the future. In other words, mean rainfall trends could reverse, with considerably increased risks for more flooding in the region.

209

Extreme rainfall in New Zealand and associated flooding events: using science to estimate attributable financial costs. Rosier, Suzanne1, Frame, Dave2, Carey-Smith, Trevor1, Dean, Sam1, Black, Mitchell T.3, Sparrow, Sarah4

Presenting author’s e-mail: [email protected]

1NIWA, Wellington, New Zealand 2Victoria University of Wellington, New Zealand 3University of Melbourne, Australia 4Oxford e-Research Centre, University of Oxford, U.K.

Session 3.9 – February 8, 2018, 1645-1700

Human-induced changes to climate are affecting rainfall patterns, leading to increased frequency and/or intensity of the most extreme events in many parts of the world, including New Zealand. Using large ensembles of model simulations of rainfall from the ‘weather@home ANZ’ experiment, both with and without anthropogenic forcing, estimates of the Fraction of Attributable Risk (‘FAR’) are made for the whole country. The most highly attributable rainfall changes are seen on the West Coast of the South Island in winter, corresponding to an increase in the prevailing westerly flow there, although coherent patterns of ‘attributability’ are also evident for many other regions as well. Combining attribution estimates with costs (and benefits) associated with climate change has long been discussed. Here we present a recent pathfinder study in which estimates of financial losses associated with twelve recent extreme rainfall events are combined with estimated values of FAR for those events. This permits an estimation of the fraction of costs attributable to anthropogenic climate change.

210

Anthropogenic and natural influences on atmospheric circulation during heatwaves in Melbourne and Perth D’Alessandro, Adrian1, King, Andrew1, Karoly, David1, Black, Mitchell1

Presenting author’s e-mail: a.d’[email protected]

1ARC Centre of Excellence for Climate System Science, School of Earth Sciences, University of Melbourne, VIC, Australia.

Session 3.9 – February 8, 2018, 1700-1715

There have been several studies investigating the roles of human-induced climate change and natural variability in Australian heat events. In contrast, the relative influences of climate change and variability on atmospheric circulation during these heat events is less well understood.

Heatwaves in Melbourne and Perth are both commonly associated with circulation patterns that cause air flow from the inland. Using indices of surface pressure gradients relevant to those locations and indicating these flow patterns, we study relationships with observed heat waves using station data and ERA-Interim reanalyses to establish the nature of the observed circulation-temperature relationship.

We then use several sets of Weather@Home-ANZ regional model simulations to analyse the relative influences of anthropogenic climate change and El Niño-Southern Oscillation (ENSO) on the frequency and magnitude of heat extremes in Melbourne and Perth. We compute the same pressure gradient indices in the model and compare between our groups of model simulations (with and without anthropogenic forcings, and under El Niño, La Niña, and neutral conditions). The Weather@Home- ANZ model ensembles are generated using volunteers’ spare computer time and provide thousands of realisations representing each of our scenarios of interest. These very large numbers of model simulations allow us to make robust statements on the roles of human-induced climate change and ENSO-related variability in both the heatwaves and the circulation associated with the heatwave events.

Our findings suggest that the Weather@Home-ANZ model performs very well in simulating both the summer temperatures in Perth and Melbourne, and the circulation associated with heatwave conditions at these locations, when compared with station data and ERA-Interim. Perth appears to have a more significant change due to anthropogenic forcings than Melbourne in both the frequency of extreme temperatures and the associated pressure indices. The role of the different ENSO phases is still being investigated.

211

The effect of increasing CO2 on the extreme September 2016 rainfall across south eastern Australia Hope, Pandora1, Lim, Eun-Pa1, Hendon, Harry1, Wang, Guomin1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Vic, Australia

Session 3.9 – February 8, 2018, 1715-1730

In 2016 Australia experienced extreme, widespread rainfall, with flooding and wild weather impacting some agriculture and power generation. It was particularly wet through winter and into early spring, with the wettest September for eastern Australia ever recorded.

Extreme rainfall on a range of timescales is expected to become more intense in a warmer world, so did increasing levels of atmospheric CO2 mean that this event was wetter than it might otherwise have been?

Using the Australian Bureau of Meteorology's seasonal forecast system, we focus on two weeks when the large-scale drivers were forecast well. The event was forecast as the second wettest of this September fortnight in the hindcast period. The event was then re-forecast using low atmospheric CO2, initialised with initial conditions from which the influence of the last 55 years of increasing CO2 had been removed. Three measures of the 'local' ingredients required for heavy rainfall were assessed – the precipitable water, the moisture divergence and the vertical static stability.

During the event the precipitable water was extremely high, the moisture convergence was high and static stability was low. However, the effect of increasing atmospheric CO2 on the extreme September 2016 rainfall across south eastern Australia was minimal, with little change in precipitable water over eastern Australia, and with changes in circulation and static stability driving a tendency towards drier conditions.

212

Severe drought in southern Australia in a warming world Henley, Benjamin J.1, King, Andrew D.1, Peel, Murray C.2, Nathan, Rory J.2, Ballis, Natasha2,1, Karoly, David J.1

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia, School of Earth Sciences 2University of Melbourne, VIC, Australia, Department of Infrastructure Engineering

Session 3.9 – February 8, 2018, 1730-1745

Severe and prolonged droughts, lasting up to one or more decades, cause significant stress on social, economic and natural systems. In particular, the reliable supply of water to large urban populations and agriculture is under threat in many parts of the world. Climate model simulations often underestimate the occurrence of persistent precipitation deficits associated with severe prolonged droughts.

In this study, we combine approaches from water resources engineering and climate modelling to infer projected changes in drought risk in southern Australia. We use stochastic rainfall-runoff modelling to represent the influence of mean state changes in temperature and precipitation on water supply drought risk. We overlay these estimates with CMIP5-simulated changes in mean rainfall and temperature in 1.5 and 2 degree warmer worlds. Our results illustrate how drought risk is projected to change under the policy-relevant targets of the Paris agreement and will inform future water planning in southern Australia.

213

3.10 Climate extremes and impacts Effects of climate variability and change on damaging hail risk Andreas, Prein F1, Holland, Greg J1

Presenting author’s e-mail: [email protected]

1National Center for Atmospheric Research, Colorado, USA

Session 3.10 – February 7, 2018, 0930-0945

A single hailstorm can cause multi-billion dollar losses if it occurs over a densely populated area. A representative example is the Sydney hailstorm of April 14th, 1999, with an estimated damage of A$2.3 billion. Despite the high impact of these storms there remains considerable uncertainty concerning the risk of damaging hail in urban areas and how this risk is effected by climate variability and change. Here we use atmospheric reanalysis data and hail observations from Australia, the conterminous United States (CONUS), and Europe within the period 1979-2015 to define environmental conditions that are favorable for damaging hail development. These favorable conditions are used to develop a synthetic hail model, which is able to capture the annual cycle and interannual variability of observed hail reports. Based on this model we present a global assessment of hail risk and its dependency on historic climate variability. By using theory and climate model data we also will discuss potential impacts of climate change on damaging hail risk.

214

Extreme rainfall characteristics in central-southern Chile and its relationship with atmospheric rivers Valenzuela, Raul1,2, Garreaud, René1,2, Viale, Maximiliano1,3

Presenting author’s e-mail: [email protected]

1Department of Geophysics, University of Chile 2Center for Climate and Resilience Research, University of Chile 3Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET, Mendoza, Argentina

Session 3.10 – February 7, 2018, 0945-1000

Central-southern Chile is the narrow strip of land along the west coast of South America, bounded to the east by the Andes cordillera. Precipitation is largely produced by mid-latitude storms, ranging from ~100 mm/year around 30°S to more than 2000 mm/year around 41°S. Extreme events have a disproportionally large impact in this region given its complex topography.

In this study, we employ 67 years of daily rainfall observations (1950-2016) between 30°S and 41°S to examine the temporal and spatial characteristics of extreme rainfall (using 90th or larger percentiles) in this region. Climate Forecast System Reanalysis (CFSR) products between 1979-2011 allow us to assess the relationship between extreme daily rainfall events, integrated water vapor transport (IVT), and atmospheric rivers (ARs) making landfall along the Chilean coast.

Monthly average number of extreme rainy days (RD) increase significantly southward but the extreme rain intensity (RI) has a peak around 36°S. There is a seasonal cycle in RD with a peak in austral wintertime, whereas RI shows no seasonal cycle. Extreme rainfall at selected reference stations (SRS) is relatively homogenous within ~100-250 km of radius. The joint distribution of CFSR-derived zonal- and meridional-IVT and daily rainfall indicates that no straightforward relationship between extreme rainfall and IVT can be established.

The mean spatial structure of IVT for all extreme rainfall days at SRS shows that AR-like structures are present during these events. However, mean AR structures from northward locations are composed by extreme days with both AR and NO-AR structures, while southward locations include almost exclusively AR structures. Since ARs are coupled with cold-frontal dynamics, these results suggest that extreme rainfall in northward locations is likely associated with IVT from AR and non-AR sources (e.g. cut off lows), while southern locations are more frequently associated with ARs from landfalling cold fronts.

215

What causes multi scaling relationships in extreme rainfalls? Johnson, Fiona1

Presenting author’s e-mail: [email protected]

1UNSW Sydney, NSW, Australia

Session 3.10 – February 7, 2018, 1000-1015

Characterising the statistical properties of hydrologic extremes is difficult due to short record lengths, poorly sited gauges and data errors. Understanding and fitting multi-duration relationships may help to strengthen the characterisation and here the duration-scaling properties of Australian annual maximum series rainfall are considered for durations from 5 minutes to 7 days.

It is found in general that the relationship between the moments of the annual maxima data and the rainfall duration generally follows two simple scaling relationships, with a common slope for durations from 5 minutes to around 30 minutes and a separate relationship evident for durations from 60 minutes to 7 days. There are some interesting spatial variations in the scaling exponents with steeper scaling relationships found close to the coast and in the southern parts of Australia.

The causes of these scaling relationships have been further investigated by relating the rainfall statistics with temperature, wind speed and other climatic variables in an attempt to explain the causative mechanisms for such patterns. This information could be useful for extrapolating extreme rainfall relationships into the future taking into account the effects of anthropogenic climate change.

216

Changes in daily temperature extremes relative to the mean and their drivers in observations and CMIP5 models Gross, Mia1, Donat, Markus1, Alexander, Lisa1

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, NSW, Australia

Session 3.10 – February 7, 2018, 1015-1030

The importance of understanding changes in extreme temperatures and how they may change in the future is underpinned by their potential to cause significant impacts on humankind. Recent studies have found that for some parts of the globe, extreme temperatures have been warming at a faster rate than the mean temperature. Here, we show that this is especially true for Northern Hemisphere extra-tropical regions. In particular, the shoulder seasons, that is, March through to May, and September through to November, show the most striking features of changes in cold extremes relative to the mean for the period 1950 - 2014. This regionally accelerated warming of cold extremes is robust across most CMIP5 models and observations. It is crucial to understand what might be driving extreme temperatures in these regions to gain insight into their behaviour in the future. Here, we investigate changes in snow cover and temperature advection in relation to changes in cold extremes relative to the mean. We find the strong warming in cold extremes in the shoulder seasons is related to decreases in snow cover and reduced cold air advection. This study provides greater understanding into extreme temperatures and temperature variability in the shoulder seasons.

217

Global climate in 2017 Trewin, Blair1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Australia

Session 3.10 – February 7, 2018, 1030-1045

The year 2017 has been very warm globally. The global mean temperature for January to July 2017 was 0.78°C above the 1961-90 mean, ranking as the second-warmest such period, behind 2016. It is likely that 2017 will rank alongside 2016 and 2015 as the world’s three warmest years, despite the lack of any significant signal in 2017 from the El Niño-Southern Oscillation (ENSO), which remained in a neutral state throughout the year. Greenhouse gas concentrations, meanwhile, continue to reach record levels.

Major heatwaves affected many parts of the world in 2017. These included Chile and eastern Australia in the 2016-17 southern hemisphere summer. During the northern hemisphere summer, southwest Asia, the southwestern United States, parts of eastern China and southern Europe also experienced significant heatwave events. Major bushfires associated with several of these heatwaves, especially in Chile, Australia, southern Europe and western North America, and significant fires also occurred in regions where they are less common, including New Zealand, Ireland and Greenland.

A major drought continued to affect parts of east Africa, especially Somalia and Kenya, with significant humanitarian consequences, but long-term drought eased early in the year in southern Africa. Italy, and parts of neighbouring countries, also suffered significant drought. In contrast, there was substantial flooding early in the year in western South America, associated with coastal warming not usually seen outside a basin-wide El Niño, whilst other regions experienced major flood impacts included Sri Lanka, Texas (associated with Hurricane Harvey), and parts of southern China.

Antarctic sea ice extent was at or near record low levels for the time of year during most of the January-August period. Arctic sea ice extent was also at record low levels during the early part of 2017, but a relatively slow summer melt season led to a seasonal minimum staying well above the 2012 record.

218

Heatwave and heat-humidity index simulation skill in Australian cities with global climate models Goldie, James1, 2, 3, Alexander, Lisa1, 2, Lewis, Sophie2, 3, Sherwood, Steven1, 2

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, UNSW Australia, Sydney, NSW, Australia. 2ARC Centre of Excellence for Climate System Science, UNSW Australia, Sydney, NSW, Australia. 3Fenner School of Environment & Society, Australian National University, Acton, ACT, Australia.

Session 3.10 – February 7, 2018, 1045-1100

A wide body of literature now establishes the harm of extreme heat on human health, and work is now emerging on the projection of future health impacts.

However, heat-health relationships vary across different populations (Gasparrini et al. 2015), so accurate simulation of regional climate is an important component of joint health impact projection.

Here, we evaluate the ability of nine Global Climate Models (GCMs) from CMIP5 to reproduce a selection of 15 health-relevant heatwave and heat-humidity indices over the historical period (1990– 2005) using the Perkins skill score (Perkins et al. 2007) in five Australian cities. We explore the reasons for poor model skill, comparing these modelled distributions to both HadISD weather station observations and gridded reanalysis data from the Australian Water Availability Project (AWAP).

Finally, we show changes in the modelled distributions from the highest-performing models under RCP4.5 and RCP8.5 greenhouse gas scenarios and discuss the implications of simulated heat stress for future climate change adaptation.

References:

Gasparrini, Antonio, Yuming Guo, Masahiro Hashizume, Eric Lavigne, Antonella Zanobetti, Joel Schwartz, Aurelio Tobias, et al. “Mortality Risk Attributable to High and Low Ambient Temperature: A Multicountry Observational Study.” The Lancet 386, no. 9991 (July 31, 2015): 369–75. doi:10.1016/S0140-6736(14)62114-0.

Perkins, S. E., A. J. Pitman, N. J. Holbrook, and J. McAneney. “Evaluation of the AR4 Climate Models’ Simulated Daily Maximum Temperature, Minimum Temperature, and Precipitation over Australia Using Probability Density Functions.” Journal of Climate 20, no. 17 (September 1, 2007): 4356–76. doi:10.1175/JCLI4253.1.

219

Recent and future changes of dry spells in Croatia Marinović, Ivana1, Cindrić, Ksenija1, Güttler, Ivan1, Pasarić, Zoran2

Presenting author’s e-mail: [email protected]

1Meteorological and Hydrological Service, Zagreb, Croatia 2Geophysical Department, Faculty of Science, University of Zagreb, Zagreb, Croatia

Session 3.10 – February 7, 2018, 1130-1145

Drought in Croatia causes the highest economic losses inflicting serious damages, especially in agricultural sector. Present study performs a systematic analysis of dry spells (DS) in Croatia. DS are defined as consecutive sequences of days having daily precipitation less than a given precipitation- per-day threshold. Here, a commonly used threshold in climate and agriculture practice, that of 5 mm is used. Daily precipitation data from a dense national rain-gauge network (forming seven climatological regions) and spanning the time period 1961–2015 are employed. First, the spatial and temporal characteristics of mean and maximum seasonal and annual DS are analyzed using the empirical orthogonal functions. Recent changes in DS are investigated with the trend estimations by means of Kendall’ tau method.

Additional period 1971–2000 is defined. For this period both observation based DS and regional climate models’ based DS analysis is performed. Regional climate models (RCMs) in the present study originate from the EURO-CORDEX initiative and are forced at their boundaries by the CMIP5 global climate models. They cover European domain at the 12.5-km horizontal resolution, resulting in a realistic orography and land-sea structures over Croatia. For the 1971–2000, RCMs’ systematic errors in terms of the DS statistics will be examined. Finally, projections and future changes in the DS statistics will be based on the RCM simulations under the high and medium greenhouse gases concentration scenarios (i.e., RCP8.5 and RCP4.5) with the focus on the climate change signal between 1971–2000 and two future periods, 2011–2040 and 2041–2070.

220

Tropical cyclone tracking in a future climate Rafter, Tony1

Presenting author’s e-mail: [email protected]

1CSIRO Climate Science Centre, VIC, Australia

Session 3.10 – February 7, 2018, 1145-1200

Tropical cyclones present one of the most hazardous natural phenomena, with their associated extreme winds, heavy rainfall, and coastal inundation through storm surge and wave action all potentially leading to catastrophic outcomes. As such, there is a great deal of interest in understanding how the distribution and intensity of tropical cyclones might respond to the enhanced warming we are facing in our future climate.

One of the most important tools we can use for projecting future climate are global climate models, such as those in the CMIP model archives. These models are, generally speaking, too coarse to accurately represent tropical cyclones, so to detect their presence we must develop detection and tracking techniques to leverage all the evidence available that can confidently indicate the presence of these storms.

Tropical cyclone detection and tracking methods have been developed over many years that use a combination of atmospheric indicators to locate these storms within coarse resolution climate models. I will show how these techniques enable us to examine the possible future climatology of tropical cyclones in the Australian region and globally; how they help to expose some shortcomings in recent generations of global models; how they have been used to create climate projection products for Australia and the Pacific region; and how we plan to utilise them in novel ways through a new Tropical Cyclone Projections Portal.

221

Forewarned is forearmed: equipping farmers and agricultural value chains to proactively manage the impacts of extreme climate events Hudson, Debra1, Hendon, Harry1, Alves, Oscar1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 3.10 – February 7, 2018, 1200-1215

Australian farmers and agribusiness operate in one of the most variable climates in the world. Extremes (such as heatwaves, frost and heavy rainfall) and climate variability are the largest drivers of annual agricultural income and production. A newly funded multi-institution 5-year project, "Forewarned is forearmed: managing the impacts of extreme climate events", will deliver direct value to farmers through providing forecasts of extremes and equipping farmers with the information and tools to be forewarned and prepared. The project is supported by funding from the Australian Government Department of Agriculture and Water Resources as part of its Rural R&D for Profit programme. The Bureau of Meteorology (BoM), working with a number of research partners, will develop and deliver forecasts of the likelihood of climate extremes on multi-week and seasonal timescales – beyond the 7-day weather forecast. This will provide farmers with the first ever forecasts of extremes weeks to seasons ahead. The forecasts will be based on BoM's seasonal forecast system, ACCESS-S. The BoM component of the project includes research to 1) evaluate user needs, 2) understand large-scale drivers (e.g., El Niño) of extremes, 3) improve ACCESS-S to give better forecasts of extremes, and 4) develop experimental forecast products which will be trialled by users to assess value. A subset of products that have sufficient accuracy and utility will be delivered as official BoM forecasts to the benefit of agriculture. Project partners who are agricultural climate and systems analysis researchers, with particular expertise in the dairy, beef, sheep, grains, sugar and wine industries, will use BoM output to determine climate extremes scenarios through appropriate risk management frameworks, farm system models and economic frameworks. The plan and scope of the project will be presented, together with some early results.

222

Big data solutions for quantifying the costs of climate risk to new critical infrastructure Mallon, Karl

Session 3.10 – February 7, 2018, 1215-1230

Critical infrastructure decisions worth billions of dollars and designed to last a century are being made every day. Most are still being made in ignorance of detailed climate impact analysis.

This paper details the development of big data software that creates a bridge between GCM and downscaled data sets, and the engineering and financial analysis needed by infrastructure decision makers. The critical focus has been on cross-cutting the vulnerability of various elements of an infrastructure asset, with the hazards being driven by extreme weather and climate change impacts and change.

The paper also considers the need to capture intrinsic uncertainty in the climate, weather and asset data sets, so that the results provide decision makers with a probabilistic insight into the range of risk and the effectiveness of their adaptation actions to mitigate risk. The paper will provide examples of the implementation of the system for Sydney Water, Seqwater and for governments in Australia, Samoa and Fiji.

The paper includes identification of the limitations being encountered with climate data sets in Australia and recommendations for agreed output standards to enable third party software systems to harness such data.

223

Climate change and the international shipping trade Cahalan, Adrienne1,2,3

Presenting author’s e-mail: [email protected]

1Weather and Climate Advisory Group 2RBG Lawyers 3Maritime Law Association of Australia and New Zealand

Session 3.10 – February 7, 2018, 1230-1245

Climate change is a fundamental driving force persuading the shipping and marine insurance industry to adapt to new requirements from governments, business and company shareholders to take into account the risks of climate change as well as expectations from customers requiring the transport of their goods without or with a minimal environmental footprint.

Issues relating to alternative fuels, improving marine vessel’s emission inventory methods, emission reductions and exhaust regulations will be briefly discussed.

Finally there will be a brief focus on climate system impacts in shipping such as transportation in the Arctic and the impact of extreme weather events on the international shipping trade and marine insurance industry.

224

3.11 Science supporting the Paris Agreement: Southern Hemisphere perspectives The global carbon budget and tracking the Paris Agreement Canadell, Pep1

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Canberra

Session 3.11 – February 5, 2018, 1645-1700

Long-term redistribution of carbon among fossil fuel reserves, the atmosphere, oceans and land largely determines the degree of human-driven climate change and future carbon-climate feedbacks. Here, I provide an update on the state and trends of the carbon budged as assessed by a large research community effort driven by the Global Carbon Project*. Key trends are: 1) the apparent stabilization in the growth of fossil fuel emissions and the likely emissions decline from land use change; 2) the continued growth in atmospheric CO2 and its recent acceleration; and 3) the growth in the land and ocean sinks in response to the growth in excess atmospheric CO2.

Current budget estimates have limitations in tracking the true level of inter-annual and decadal variability of the land and ocean CO2 sinks. This limited understanding, in turn, prevents the use of trend dynamics to track collective progress towards the agreed National Determined Commitments and ultimate the target of remaining well below 2°C above pre-industrial levels.

I’ll discuss key uncertainties in the carbon budget and research needs to align the characterization of sub-decadal and decadal trends and variability of biogeochemical fluxes to the needs of climate policy in the rise of the new greenhouse gas regime under the Paris Agreement.

* http://www.globalcarbonproject.org

225

The Carbon Dioxide Removal Model Intercomparison Project (CDR-MIP): Rationale and experimental design Lenton, Andrew1,2, Keller, David P.3, Scott, Vivian4, Vaughan, Naomi E.5, Bauer, Nico6, Ji, Duoying7, Jones, Chris D.8, Kravitz, Ben9, Muri, Helene10, Zickfeld, Kirsten11

1CSIRO Oceans and Atmosphere, Hobart, Australia 2Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Australia 3GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany 4School of GeoSciences, University of Edinburgh 5Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich, UK. 6Potsdam Institute for Climate Impact Research, Research Domain Sustainable Solutions, 14473 Potsdam, Germany 7College of Global Change and Earth System Science, Beijing Normal University, Beijing, China 8Met Office Hadley Centre, Exeter, UK, 9Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA. 10Department of Geosciences, University of Oslo, Oslo, Norway. 11Department of Geography, Simon Fraser University, Burnaby, Canada

Session 3.11 – February 5, 2018, 1700-1715

The recent IPCC reports state that continued anthropogenic greenhouse gas emissions are changing the climate threatening "severe, pervasive and irreversible" impacts. Slow progress in emissions reduction to mitigate climate change is resulting in increased attention on what is called Geoengineering, Climate Engineering, or Climate Intervention – deliberate interventions to counter climate change that seek to either modify the Earth's radiation budget or remove greenhouse gases such as CO2 from the atmosphere. When focused on CO2, the latter of these categories is called Carbon Dioxide Removal (CDR). The majority of future emission scenarios that stay well below 2 °C, and nearly all emission scenarios that do not exceed 1.5 °C warming by the year 2100, require some form of CDR. At present, there is little consensus on the impacts and efficacy of the different types of proposed CDR. To address this need the Carbon Dioxide Removal Model Intercomparison Project (or CDR-MIP) was initiated. This project brings together models of the Earth system in a common framework to explore the potential, impacts, and challenges of CDR. Here, we describe the first set of CDR-MIP experiments that are designed to address questions concerning CDR-induced climate "reversibility", the response of the Earth system to direct atmospheric CO2 removal (direct air capture and storage), and the CDR potential and impacts of afforestation/reforestation, as well as ocean alkalinization.

226

Australia’s Earth System Model: ACCESS-ESM Ziehn, Tilo1, Law, Rachel1, Lenton, Andrew2

Presenting author’s e-mail: [email protected]

1CSIRO Oceans & Atmosphere, VIC, Australia 2CSIRO Oceans & Atmosphere, TAS, Australia

Session 3.11 – February 5, 2018, 1715-1730

Future levels of warming and ocean acidification depend not only on carbon emissions but also on carbon uptake by the land and the ocean. Earth system models (ESMs) are well suited to assess the response of the global carbon cycle to changes in atmospheric CO2 concentrations and climate including the carbon-concentration and carbon-climate feedbacks. The Australian Community Climate and Earth System Simulator (ACCESS) has recently been extended by adding land and ocean carbon cycle components to form an ESM, namely ACCESS-ESM. The first version of ACCESS-ESM, ACCESS- ESM1, has been extensively tested and validated by performing historical and future scenario simulations.

Here we will focus on more specific applications of ACCESS-ESM. This may include the removal of CO2 from the atmosphere (i.e. through Geoengineering) or the assessment of near term projections using various emission scenarios and their implications for the Paris agreement. We will also present progress on developing the second ESM version, ACCESS-ESM2.

227

Budgets of CO2, CH4 and N2O fluxes in the southern land and ocean Patra, Prabir1, Matthews, Naveen1

Presenting author’s e-mail: [email protected]

1RCGC/IACE, Japan Agency for Marine-Earth Science and Technology, Japan

Session 3.11 – February 6, 2018, 0930-0945

We estimated fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) using the JAMSTEC’s AGCM-based chemistry-transport model (ACTM) and observations at surface sites around the globe (Saeki and Patra, GOSL, 2017; Patra et al., JMSJ, 2016; Thompson et al., ACP, 2014). The estimated fluxes have been validated using independent aircraft observations. The effect of north-to- southern hemispheric ratio in hydroxyl (OH) (Patra et al., Nature, 2014) on CH4 inversion results is clarified. Clear partitioning of the fluxes by inverse modelling will be presented in the meeting.

228

Comparing data from the Australian greenhouse gas observation network with a high resolution model Loh, Zoë1, Law, Rachel1, Krummel, Paul1, Stavert, Ann1, Etheridge, David1, Agusti-Panareda, Anna2

Presenting author’s e-mail: [email protected]

1CSIRO Oceans & Atmosphere, Climate Science Centre, Aspendale, Australia 2ECMWF, Reading, Berkshire, UK

Session 3.11 – February 6, 2018, 0945-1000

The Australian Greenhouse Gas Observation Network (AGGON), is operated by CSIRO in collaboration with the Bureau of Meteorology and the Australian Antarctic Division. AGGON provides in situ measurements of CO2 and CH4 at minutely resolution, which are then delivered to the World Meteorological Organisation (WMO) Global Atmosphere Watch (GAW) program via the World Data Centre for Greenhouse Gases (WDCGG).

The Copernicus Atmosphere Monitoring Service (CAMS) provides a high resolution (9 km) forecast for both CO2 and CH4, driven by European Centre for Medium-Range Weather Forecast (ECMWF) Numerical Weather Prediction (NWP) model, including the use of tagged CO2 tracers to aid attribution to particular sources or sinks. In this presentation, we compare how well the high resolution model captures the observed variability in CO2 and CH4 at a number of AGGON sites. This type of assessment is crucial to improving the science required to support the Paris Agreement.

229

Methane emissions through soil in coal seam gas development area, Queensland Lafleur, Dimitri1, Fest, Benedikt1, Rayner, Peter1

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia

Session 3.11 – February 6, 2018, 1000-1015

Methane emissions from oil and gas developments are calculated using either emission factors or field measurements. In Queensland, the coal seam gas industry relies predominantly on emission factors. Coal seam gas is produced by depressurising the coal seams, thereby desorbing the gas from the coals and enabling flow to production wells. Some of this mobile gas might migrate upward using geological faults and heterogeneous stratigraphy and may be released into the atmosphere as so called migratory methane emissions. While methane emission measurements from the coal seam gas industry are scarce in general, there is very little empirical data available to ascertain the level of migratory methane emissions through the soil in the coal seam gas development area.

Soil flux chamber measurements and soil samples are taken to establish whether methane is seeping through the soil. The measurements are taken across fault transects and background transects. Background soil flux chamber measurements away from the faults show the expected soil methane uptake. At several locations across the fault transects methane emissions are measured. Lab soil incubations confirm that all soil is taking up methane. This finding suggests that the source of methane is situated below the soil layer. δ13C-CH4 measurements indicate that the source is unlikely from local biology. It cannot be concluded that the faults were instrumental in mobilising the methane.

This result informs the debate on the role of the coal seam gas industry and Australia’s emission reduction pledge for Paris. The oil and gas industry is committed to methane emissions that are less than 0.1% of total gas production. The fieldwork demonstrates what would be necessary to set up a monitoring system for a fossil fuel industry that aims to provide fossil fuels to a world that requires increasingly more stringent emission reductions to adhere to the Paris agreement.

230

Quantification of urban CO2 emissions Turnbull, Jocelyn1,2, Keller, Elizabeth1, Thompson, Jeremy1, Mikaloff Fletcher, Sara3, Brailsford, Gordon3, Davis, Kenneth4, Lauvaux, Thomas4, Miles, Natasha4, Richardson, Scott4, Sweeney, Colm2, Shepson, Paul6, Heimburger, Alexie6, Gurney, Kevin7, Karion, Anna8

Presenting author’s e-mail: [email protected]

1Rafter Radiocarbon Laboratory, GNS Science, Lower Hutt, New Zealand 2University of Colorado, USA 3NIWA, Wellington, New Zealand 4Pennsylvania State University, USA 6Purdue University, Indiana, USA 7Arizona State University, USA 8NIST, Maryland, USA

Session 3.11 – February 6, 2018, 1015-1030

Urban areas account for only about 3% of Earth’s surface area, but more than 70% of fossil fuel derived

CO2 emissions. Cities are often leading the way in CO2 emission mitigation efforts, both to address the climate challenge and the many associated co-benefits for urban areas. Cities need to understand their urban-scale emissions both to assess the potential of low-carbon and carbon mitigation strategies, and to evaluate the success of such strategies. Commonly, national-level CO2 reporting is downscaled to provide city-scale emission estimates, but it is difficult to assess the accuracy of these estimates. Different downscaling methods can produce differences of 50-100% for an individual city, too uncertain to provide meaningful guidance on typical emission reduction targets of 20-30%.

In recent years, efforts to develop methods to assess urban CO2 emissions have begun in several cities globally. We will showcase methodologies developed in the long-running Indianapolis Flux Experiment (INFLUX) and show how they can be applied to other cities around the world. INFLUX brings together new high-resolution (in both space and time) inventory assessments, a multi-year record of in situ CO2,

CH4 and CO from tower-based and aircraft-based atmospheric measurements along with a complementary suite of 50 trace gases and isotopes from flasks collected at the same sites, and atmospheric modelling. Together, these provide high-accuracy, high-resolution, continuous monitoring of emissions of GHGs from the city. We show that feedback from the atmospheric observations results in substantial improvement in the inventory assessment. The combined methods can constrain urban fossil fuel CO2 emissions to better than 10%, sufficient to allow assessment of proposed emission reduction targets. We will also present early results from a new study in Auckland, where we use similar methods with a particular focus on assessing the land carbon sink that may partially offset urban fossil fuel CO2 emissions.

231

3.12 Processes, impacts and likelihood of severe droughts in the Southern Hemisphere Paleoclimate perspectives on historical and future drought risk in eastern Australia Cook, Benjamin I1, Cook, Edward2, Palmer, Jonathan3

Presenting author’s e-mail: [email protected]

1NASA Goddard Institute for Space Studies, New York, USA 2Lamont-Doherty Earth Observatory, New York, USA 3University of New South Wales, Sydney, New South Wales, Australia

Session 3.12 – February 9, 2018, 0930-0945

Eastern Australia recently experienced an intense drought (Millennium Drought, 2003–2009) and record-breaking rainfall and flooding (austral summer 2010–2011). There is some limited evidence for a climate change contribution to these events, but such analyses are hampered by the paucity of information on long-term natural variability. Analyzing a new reconstruction of summer (December- January-February) Palmer Drought Severity Index (the Australia-New Zealand Drought Atlas; ANZDA, 1500-2012 Common Era), we find moisture deficits during the Millennium Drought fall within the range of the last 500 years of natural hydroclimate variability. This variability includes periods of multidecadal drought in the 1500s more persistent than any event in the historical record. However, the severity of the Millennium Drought, which was caused primarily by autumn (March-April-May) precipitation declines, may be underestimated in the ANZDA because the reconstruction is biased toward summer and antecedent spring (September-October-November) precipitation. The pluvial in 2011, however, which was characterized by extreme summer rainfall that is faithfully captured in the ANZDA, is likely the wettest year in the reconstruction for Coastal Queensland. Climate projections (Representative Concentration Pathway 8.5 scenario) suggest that eastern Australia will experience increased drought risk and incidence of wet extremes in the 21st century equal to, or exceeding, the recent Millennium Drought and 2011 pluvial. Significant uncertainties remain to be comprehensively assessed, however, especially regarding land surface and vegetation processes that will likely mediate drought impacts at the land surface (e.g., CO2 fertilization).

232

The 2010-2015 mega drought in Central Chile: Impacts on regional hydroclimate and vegetation Garreaud, René1,2

Presenting author’s e-mail: [email protected]

1Department of Geophysics, University of Chile 2Center for Climate and Resilience Research, University of Chile

Session 3.12 – February 9, 2018, 0945-1000

Since 2010 an uninterrupted sequence of dry years, with annual rainfall deficits ranging from 25 to 45%, has prevailed in Central Chile (western South America, 30-38°S). Although intense 1- or 2-year droughts are recurrent in this Mediterranean-like region, the ongoing event stands out because of its longevity and large extent. The extraordinary character of the so-called Central Chile mega drought (MD) was established against century long historical records and a millennial tree-ring reconstruction of regional precipitation. The largest MD-averaged rainfall relative anomalies occurred in the northern, semi-arid sector of central Chile but the event was unprecedented to the south of 35°S. ENSO neutral conditions have prevailed since 2011 (but for the strong El Niño 2015) contrasting with La Niña conditions that often accompanied past droughts. We were able to show that climate change contribute to at least one third of the MD.

The precipitation deficit diminished the Andean snowpack and resulted in amplified declines (up to 90%) of river flow, reservoir volumes and groundwater levels along central Chile and westernmost Argentina. In some semiarid basins we found a decrease in the runoff-to-rainfall coefficient. A substantial decrease in vegetation productivity occurred in the shrubland-dominated, northern sector, but a mix of greening and browning patches occurred farther south where irrigated croplands and exotic forest plantations dominate. The ongoing warming in central Chile, making the MD one of the warmest 6-year period on record, may have also contributed to such complex vegetation changes by increasing potential evapotranspiration. The understanding of the nature and biophysical impacts of the MD contributes to preparedness efforts to face a dry, warm future regional climate scenario.

233

Using instrumental, palaeoclimate, and climate model data to better understand what is plausible with respect to historical and future rainfall – a case study from the Lockyer Catchment, southeast Queensland, Australia Armstrong, Matthew1, Kiem, Anthony S.1

Presenting author’s e-mail: [email protected]

1Centre for Water, Climate and Land (CWCL), University of Newcastle, NSW, Australia

Session 3.12 – February 9, 2018, 1000-1015

Future rainfall projections are usually presented as a percentage change from current climate, where current climate is defined using relatively short instrumental records. However, palaeoclimate reconstructions demonstrate that instrumental data (i.e. post-1900) does not capture the full range of past natural climate variability (i.e. pre-1900). Understanding the natural climate variability, and how it compares to climate model projections for the future, requires the use of (a) instrumental and palaeoclimate data to quantify the range of historical variability and (b) climate model data to quantify if/how things could change in the future.

In this study we investigate whether the risk of dry years is higher/lower in (a) palaeoclimate data (pre-1900) than in instrumental records and (b) future climate model projections than in both instrumental and palaeoclimate data. In other words, is the difference between current conditions and the driest futures projected by climate models greater than the range of variability seen in the past (instrumental and palaeoclimate)? Also tested is the difference in the ‘worst case scenario’ if climate change projections applied to the instrumental record are compared to climate change projections applied to the combined instrumental and palaeoclimate record.

For our case study we found that out to at least 2100, for all climate model and emission scenario combinations, the risk of ‘dry’ annual rainfall conditions was within the confines of variability in the palaeoclimate record. However, the ‘dry’ event with a 3% chance of occurring in the instrumental period has ~33% chance of occurring when plausible climate model projections for 2080-2100 are considered in conjunction with the full range of variability seen in the palaeoclimate data. These results highlight that significant uncertainties exist when estimating current and future climate risks and that water resources managers need to consider, and adapt to, a wider range of plausible scenarios.

234

Using reconstructions of winter and summer hydroclimate in western Tasmania Allen, Kathryn1, Evans, Rob2, Allie, Stuart3, Carson, Greg3, Baker, Patrick1

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia 2Silvican Pty Ltd, VIC, Australia 3HydroTasmania, TAS, Australia

Session 3.12 – February 9, 2018, 1015-1030

Water resource availability is critical for agriculture, environmental flows, hydroelectric energy production and supply of drinking water but short (mostly < 100 years) instrumental records in Australia limit understanding of hydroclimatic variability. We present three multi-centennial seasonal hydroclimatic reconstructions (dam inflows) for Tasmania based on tree-rings, two for the summer months (Dec-Feb) and one for winter months (Jul-Aug). The two summer reconstructions are for a northern and a western catchment. We also present a winter (Jul-Aug) reconstruction for western Tasmania. All three reconstructions are based on a mixture of ring width and wood properties chronologies (e.g. tracheid radial diameter, cell wall thickness, density, microfibril angle). The two summer reconstructions explain ~35% (southwest) and ~32% (north) of the variance in inflows. While there are some strong similarities between the two, there are also some important differences, especially in relation to the timing and severity of extreme events. Both reconstructions suggest decreased flows ~1520CE, but this event appears much more extreme in the northern reconstruction. In general, current conditions are well within the range of variability over the past nine centuries. The much shorter (1731 – 2007 CE) and weaker winter reconstruction for the west explains ~ 23% of inflows but is the first successfully verified winter season reconstruction for the region. It suggests that winters for the past ~150 years have generally been drier than for the previous ~150 years. Conditions more extreme than those in the 20th Century have occurred in the past for both seasons. Differences between both the regional and the seasonal reconstructions demonstrate the relevance of highly resolved seasonal and regional information for southeastern Australia. We use our reconstructions to discuss the probability of low flow events more severe than those observed in the instrumental record for this region.

235

The impact of ocean variability on tropical rainfall Taschetto, Andréa S.1, Sen Gupta, Alex1, Ummenhofer, Caroline C.2, England, Matthew H.1

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre and ARC Centre of Excellence for Climate Extremes, University of New South Wales, NSW, Australia 2Department of Physical Oceanography, Woods Hole Oceanographic Institution, MA, USA

Session 3.12 – February 9, 2018, 1030-1045

Variations in ocean temperature can cause fluctuations in rainfall, generating droughts and wet periods over land. The El Niño – Southern Oscillation (ENSO) is the most well-known driver of droughts in many parts of the world. Droughts however can occur due to causes unrelated to ocean temperature, for example, as a result of intrinsic atmospheric and land variability. Disentangling the contribution of each climate component to drought frequency, intensity and persistence can be a complicated, if not impossible task, using observations.

This study assesses the contribution of sea surface temperature variability to droughts over land within a state-of-the-art climate model. The National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) is used to perform three sets of numerical experiments: i. a fully coupled simulation, ii. an atmospheric simulation forced with interannually-varying sea surface temperature and sea-ice derived from (i), and iii. an atmospheric simulation forced with the long term seasonal sea surface temperature and sea-ice climatologies over the global oceans derived from (i). All experiments are integrated for 500 years. The different responses of rainfall variability simulated over land are investigated on interannual to multidecadal timescales.

Results show that, as expected, interannual variations of sea surface temperature play an important role in increasing rainfall variability everywhere in the globe. More surprising is the fact that mean rainfall is affected by ocean variability, with some regions receiving more rainfall and others less.

In addition, droughts are more severe in the presence of ocean variability. Interestingly, the duration of multiyear drought events are similar in the simulations with and without variations in sea surface temperature. This suggests that despite making droughts worse, ocean variability does not add predictive skill for duration of long term drought events.

236

Correlation between drought indices and soil moisture data and their application for evaluation of drought characteristics Hoffmann, David1,2, Arblaster, Julie1,2,3, Gallant, Ailie1,2

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia 2ARC Centre of Excellence for Climate Extremes 3National Center for Atmospheric Research

Session 3.12 – February 9, 2018, 1045-1100

Drought is a stochastic natural hazard and an inherent part of climate variability that affects most parts of the Earth. It is the persistence of extreme negative precipitation anomalies over a specific region for an extended period of time and is most likely to occur in regions with a highly variable climate.

Disagreement results from conflicting concepts of droughts and their different characteristics and definitions. Here we evaluate the importance of evapotranspiration by comparing two different drought indices estimating this hazard using meteorological and hydrological parameters. The Standardised Precipitation Index (SPI) and the Palmer Drought Severity Index (PDSI) have become popular drought indices due to simplicity (SPI) and long term use (PDSI). Criticism arises either in terms of their complexity and the lack of data availability (PDSI) or their loose connection to ground conditions when only obtaining one drought proxy such as precipitation (SPI). Soil moisture is a key proxy as it directly affects the environment when depleted but is also difficult to measure over a wide area and existing sparsely stationary measurements are not representative for bigger domains and statistical purposes. Alternatives are to either use soil moisture as an output from a land surface model (Global Land Data Assimilation System (GLDAS)) or remotely estimated values from monthly anomalies of satellite-observed liquid water equivalent thickness (Gravity and Climate Experiment (GRACE)). In this study these soil moisture estimates are compared with the mentioned drought indices and correlated over the available time period to date. Results are generally showing a very inhomogeneous picture with strong relationships between soil moisture and drought estimates over South Africa, America, Australia, eastern Asia and parts of Eurasia but no correlation over most arid and semi-arid land masses. Differences across these drought measures in terms of onset, duration, severity and cessation are also examined.

237

3.13 Palaeoclimate reconstruction and modelling Sensitivity of Antarctica to ocean warming during the last interglacial Turney, Chris S. M.1,2,3, Fogwill, Christopher J.1,2,4, Golledge, Nicholas R.5,6, McKay, Nicholas P.7, van Sebille, Erik2,8,9, Jones, Richard T.10, Etheridge, David11, Rubino, Mauro4,11,12, Thornton, David P.11, Davies, Siwan M.13, Thomas, Zoë1,2,3, Bird, Michael I.14,15, Munksgaard, Niels C.14,16, Kohno, Mika17, Woodward, John18, Winter, Kate18, Rootes, Camilla M.19, Millman, Helen2, Rivera, Andres20, van Ommen, Tas21,22, Curran, Mark21,22, Moy, Andrew21,22, Rahmstorf, Stefan23, Cooper, Alan24,25

Presenting author’s e-mail: [email protected]

1Palaeontology, Geobiology and Earth Archives Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Australia 2Climate Change Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Australia 3ARC Centre of Excellence in Australian Biodiversity and Heritage, School of Biological, Earth and Environmental Sciences, University of New South Wales, Australia 4School of Geography, Geology and the Environment, Keele University, ST5 5BG, UK 5Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand 6GNS Science, Avalon, Lower Hutt, New Zealand 7School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA 8Grantham Institute & Department of Physics, Imperial College London, London, UK 9Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, Netherlands 10Department of Geography, Exeter University, Devon, EX4 4RJ, UK 11Climate Science Centre, CSIRO Ocean and Atmosphere, Aspendale, Victoria, 3195 Australia 12Dipartimento di Matematica e Fisica, Università della Campania “Luigi Vanvitelli”, viale Lincoln, 5- 81100 Caserta, Italy 13Department of Geography, Swansea University, Swansea, UK 14Centre for Tropical Environmental and Sustainability Science, College of Science, Technology and Engineering, James Cook University, Cairns, Australia 15ARC Centre of Excellence in Australian Biodiversity and Heritage, James Cook University, Cairns, Australia 16Research Institute for the Environment and Livelihoods, Charles Darwin University, Australia 17Department of Geochemistry, Geoscience Center, University of Göttingen, Goldschmidtstr. 1, 37077 Göttingen, Germany 18Department of Geography, Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK 19Department of Geography, University of Sheffield, UK 20Glaciology and Climate Change Laboratory, Centro de Estudios Cientficos, Valdivia, Arturo Prat 514, Chile 21Department of the Environment and Energy, Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania 7050, Australia 22Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart, Tasmania 7001, Australia 23Potsdam Institute for Climate Impact Research (PIK), Earth System Analysis, Potsdam 14473, Germany 24Australian Centre for Ancient DNA, University of Adelaide, Australia 25ARC Centre of Excellence in Australian Biodiversity and Heritage, University of Adelaide, Australia

238

Session 3.13 – February 8, 2018, 0930-0945

The Last Interglacial (130 to 116 thousand years ago) is widely considered to have been warmer than today, but the timing and contribution of Antarctica to global sea level rise during this period remains uncertain. Here we report a new highly-resolved blue ice record close to the West Antarctic Ice Sheet grounding line that implies substantial mass loss prior to peak Last Interglacial warming. To explore the extent and magnitude of associated changes we use a global network of marine records corrected for ocean current drift to drive an ice sheet model. We find a warming of 2˚C in annual Southern Ocean sea surface temperatures relative to 1981-2010 is sufficient for Antarctica to have contributed 3.2 metres equivalent global sea level within the first millennium of forcing. Our results demonstrate that the Antarctic ice sheets are highly sensitive to pervasive ocean warming, with important implications for future sea-level rise.

239

Westerly wind variability at sub-Antarctic Macquarie Island: Links to the Southern Annular Mode and Southern Hemisphere temperature Saunders, Krystyna M1,2, Dätwyler, Christoph2, Neukom, Raphael2, Roberts, Stephen J3, Sime, Louise3, Grosjean, Martin2, Hodgson, Dominic A3

Presenting author’s e-mail: [email protected]

1Australian Nuclear Science and Technology Organisation, NSW, Australia 2University of Bern, Switzerland 3British Antarctic Survey, United Kingdom

Session 3.13 – February 8, 2018, 0945-1000

The position and strength of the Southern Hemisphere westerly winds is important for temperature and rainfall variability from the mid- to high-latitudes of the Southern Hemisphere. They also influence Southern Ocean circulation and sea ice extent around Antarctica and are closely linked to changes in the Southern Annular Mode (SAM). While observations since the 1950s show the winds have strengthened and shifted southwards, this period is too short to understand their natural variability, especially as stratospheric ozone depletion and rising greenhouse gases from anthropogenic activities are considered to be driving these changes. Here we present a multi-decadal Southern Hemisphere westerly wind strength reconstruction for the last 1600 years from sub-Antarctic Macquarie Island (54°S, 158°E). The reconstruction is based on the application of a diatom-sea spray transfer function. This transfer function was used to assess changes in sea spray inputs to a small, exposed lake on the western edge of the Macquarie Island plateau, where the amount of sea spray is directly related to the strength of the westerlies. In contrast to most previous estimates of past westerly wind variability, our record is situated in the core region of the wind belt. It therefore allows a more direct interpretation of westerly wind behaviour not dependent on potentially unstable teleconnections. The reconstruction shows close agreement with the southern South America temperature (Past Global Changes) and SAM reconstructions for much of the last Millennium. Together with spatial correlation maps from instrumental, reanalysis and modelling data, this demonstrates that changes recorded at Macquarie Island are representative of wind and temperature across the mid- to high-latitudes of the Southern Hemisphere.

240

Abrupt early deglacial atmospheric CO2 increase driven by Southern Hemispheric westerlies Menviel, Laurie, Spence, Paul, Yu, J., Chamberlain, Matt, Matear, Richard, Meissner, Katrin, England, Matthew

Session 3.13 – February 8, 2018, 1000-1015

The early phase of the deglaciation, corresponding to Heinrich stadial 1 (HS1, ~17.6-14.7 ka), is a crucial period to understand as it represents the runaway of the climate and carbon cycle system into an interglacial state. A weakening of North Atlantic Deep Water (NADW) formation during HS1 kept Greenland in a glacial state, while the temperature at high southern latitudes increased and atmospheric CO2 rose by 40 ppm in two abrupt phases. Results of a series of transient simulations performed with a carbon-isotope enabled Earth system model, suggest that the two abrupt phases of

CO2 increase can be explained by CO2 outgassing from the Southern Ocean due to stronger southern hemispheric westerlies. This is confirmed by a wind perturbation experiment performed with a global ocean eddy-permitting model. In addition, we show that the associated Southern Ocean deep convection increases the meridional heat transport to high southern latitudes, thus generating a positive feedback between SST increase, sea-ice decrease and atmospheric CO2 rise.

241

Using palaeoclimate data and models to detect climate and environmental tipping points in the Earth System Thomas, Zoë1, Turney, Chris1, Golledge, Nicholas2, Palmer, Jonathan1

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia 2Victoria University of Wellington, Wellington, New Zealand

Session 3.13 – February 8, 2018, 1015-1030

‘Tipping points’ in the Earth system are characterised by a nonlinear response to gradual forcing, and may have severe and wide-ranging impacts. Many abrupt events result from simple underlying system dynamics termed ‘critical transitions’ or ‘bifurcations’. However, since instrumental records are generally too short to provide insights on thresholds in different climatic states, one of the best ways to identify and potentially predict threshold behaviour in the climate system is through analysis of palaeoclimate data and models.

Specifically, on the approach to a tipping point, early warning signals can be detected as characteristic fluctuations in a time series as a system loses stability. Testing whether these early warning signals can be detected in highly complex real systems is a key challenge, since much work is either theoretical or only tested with simple models. Here we explore the identification of early warning signals using two datasets. First we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. We find that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points. Our second example is based on the eastern

Australia and New Zealand Drought Atlas (ANZDA), a seasonally resolved gridded spatial reconstruction of drought and wet periods over the past 500 years based on a network of tree-ring chronologies and a coral record. Here we examine hydroclimate extremes and the development of spatial and temporal indicators prior to tipping. We demonstrate that time series precursors from palaeoclimate data provide a powerful means of forewarning tipping points within the Earth System.

242

From Antarctic ice cores to Australia’s climate: hydroclimate reconstructions using an alternative proxy Tozer, Carly1,2,*, Kiem, Anthony2, Vance, Tessa1, Roberts, Jason3, Curran, Mark3, Moy, Andrew3

Presenting author’s e-mail: [email protected]

1Antarctic Climate & Ecosystems Cooperative Research Centre, Hobart, Australia 2Centre for Water, Climate & Land, University of Newcastle, NSW, Australia 3Australian Antarctic Division, Kingston, Tasmania, Australia

Session 3.13 – February 8, 2018, 1100-1115

Research worldwide shows that rainfall and streamflow (hydroclimate) reconstructions developed from paleoclimate proxy records provide more information on the range of climate variability possible than the short instrumental records water resource management plans are currently based on. Hence there is a clear need for the development of hydroclimate reconstructions to allow us to better manage our water resources into the future. In Australia, however, there is a lack of local high resolution proxies, particularly in catchments of interest, and as such the utility of remote proxies for developing hydroclimate reconstructions is being investigated. Here we exploit a teleconnection between summer sea salt deposition recorded in ice cores from East Antarctica and climate variability in eastern Australia to produce millennial-length, annual rainfall and streamflow reconstructions for a case-study catchment on Australia’s eastern seaboard. The reconstructions show periods of higher hydroclimatic variability relative to the instrumental era, longer wet and dry epochs and importantly, that wet (dry) epochs in the rainfall record are shorter (longer) in the streamflow record. This has implications for interpreting rainfall proxies as water availability and also for our understanding of the rainfall-runoff relationship in protracted wet and dry periods. Furthermore, the variation in the distribution of the duration of wet and dry epochs between centuries suggests that water resources management and planning based on the statistics of the last 100 years of data (or less) is problematic. This information provides a better understanding of present infrastructure vulnerability in the context of past climate variability. In addition this work emphasises a novel combination of ice core science, paleoclimatology and catchment-scale hydrology that is now being used to develop more robust water resources planning and management.

*now at CSIRO Oceans & Atmosphere, Hobart, Australia

243

New Millennial-length summer temperature reconstructions for southeastern Australia Allen, Kathryn1, Cook, Edward2, Buckley B. M.2, Evans, Rob3, Baker, Patrick1

Presenting author’s e-mail: [email protected]

1School of Ecosystem and Forest Sciences, University of Melbourne, VIC, Australia 2Lamont-Doherty Earth Observatory, Palisades, NY, USA 3Silviscan Pty Ltd. VIC, Australia

Session 3.13 – February 8, 2018, 1115-1130

An evolving understanding of past climate variability and changes observed over the 20th Century requires integration of high quality palaeoclimate records into analyses. To this end, we have developed two nested 979-year mean temperature records for Tasmania over the Austral summer (December – February) based solely on Tasmanian tree-rings. The first model is based on all potential tree-ring predictors available (unrestricted reconstruction), and the second constrained to use records only from Lagarostrobos franklinii, a species particularly sensitive to summer temperatures (restricted reconstruction). Unlike the previous Mt Read L. franklinii reconstruction for the November-April period, our reconstructions depend not only on the ring widths but also, crucially, on wood properties such as density, tracheid radial diameter and cell wall thickness. Both reconstructions explain between ~50 and 66% of the variance for each nest, although the restricted reconstruction exhibits superior verification statistics. Extreme periods are more amplified in the restricted reconstruction than the unrestricted reconstruction. Both reconstructions show strong positive relationships with temperatures over southeastern Australia and moderate negative relationships with temperatures in the coastal northeast of the continent. We find that the periods centred on 1300, 1320 and 1500 CE were as warm as the most recent period, but that the elevated temperatures since ~1950 - shown as a step-change in our reconstruction - have persisted longer than any of the three earlier periods. The strength of our reconstruction and its spatial signature highlight the potential for high quality sub- regional reconstructions where multiple large-scale ocean-atmosphere processes drive climate over broader regions.

244

Pacific ENSO variability during the 13th to 15th centuries Hunter, Jasmine1, McGregor, Helen1, Wong, Henri2, Fischer, Matthew2, Devriendt, Laurent1, Gagan, Michael3, Zhou, Jian-xin4, Woodroffe, Colin1, Fink, David2, Faddy-Vrouwe, Robert1

Presenting author’s e-mail: [email protected]

1University of Wollongong, NSW, Australia 2Australian Nuclear Science and Technology Organisation, NSW, Australia 3Australian National University, ACT, Australia 4University of Queensland, QLD, Australia

Session 3.13 – February 8, 2018, 1130-1145

The El Niño Southern Oscillation (ENSO) represents one of the largest sources of interannual climatic variation worldwide. While the mechanisms behind ENSO are focused in the Pacific, the resulting teleconnection influences climate globally, meaning that understanding the response of ENSO to climate variation is vital to assess 20th century ENSO variability within context. Over the past millennium, ENSO variability has shown cycles of quiescence and amplification over inter-decadal and centennial timescales, with several records indicating enhanced ENSO variability during anomalously warm conditions. Particularly, the 13th-15th centuries witness two recent periods of global change, with many records depicting a shift from a warm period known as the Medieval Climate Anomaly (MCA, ~900-1250AD) to a cooler Little Ice Age (LIA, ~1400-1750AD) period. However, there is disagreement regarding the spatial extent and scale of these deviations from mean conditions, and their influence on ENSO. A contributing factor is the scarcity of records in the tropical Pacific and southern Hemisphere.

This study presents a monthly-resolved coupled Sr/Ca and 18O record for three Porites corals from Kiritimati Island in the central equatorial Pacific NINO3.4 region. The combined record reconstructs sea surface temperature (SST) and sea surface salinity (SSS), providing three 35- to 50-year long windows into ENSO variation within the 13th-15th centuries. The combined record shows a mean SST (26.9 ± 1.6°C) similar to the modern average (27.5 ± 1.0°C), and clear annual and interannual ENSO cycles. The ENSO amplitude shows interdecadal variability within and between each coral window. Results suggest that ENSO can respond to volcanic forcing, with anomalous warming and cooling in the years following a volcanic eruption in the 1450s. Overall, this record helps characterise ENSO behaviour in this MCA-LIA transition, and through further comparison with published data and models, provides context for 20th century climate assessment.

245

An extended record of Indian Ocean Dipole variability from Indonesian Corals Ellis, Bethany1,2, Abram, Nerilie1,2

Presenting author’s e-mail: [email protected]

1Research School of Earth Sciences, The Australian National University 2ARC Centre of Excellence for Climate System Science and ARC Centre of Excellence for Climate Extremes

Session 3.13 – February 8, 2018, 1145-1200

The Indian Ocean Dipole (IOD) is an ocean-atmosphere climate oscillation within the Indian Ocean basin and one of Australasia’s key climate drivers that influences the distribution of rainfall across the region. Future projections of IOD activity suggests that extreme positive IOD events may become more frequent with greenhouse warming leading to an increase in occurrence of extreme climate and weather events in regions influenced by the IOD. However, the short duration of instrumental records and biases in model representations of the IOD make it difficult to confidently separate anthropogenic-related trends from natural variability. To better understand natural IOD variability, high-resolution reconstructions of the Indian Ocean sea surface temperature (SST) are needed to provide a comprehensive view of IOD upwelling activity prior to the Industrial Revolution.

In this research, a fossil Porites coral has been used reconstruct past SST from the Sunda Strait, between the Indonesian islands of Java and Sumatra. The southern Sunda Strait (6.5ºS, 105.5ºE) area is a key area for measuring IOD activity, as the cold upwelling waters in the eastern Indian Ocean, associated with a positive IOD event have a clear signature here that is captured by geochemical changes in coral skeletal material. The focus of this project is on a 200 year, ~monthly resolution ∂18O record from a coral tsunami block that spans the interval 1670 to 1872. The coral temperature record has been added onto ICOADS ship log book records and modern instrumental data of the region to create a 350-year record of tropical Indian Ocean SSTs. This extended SST reconstruction reveals insights into the frequency and intensity of positive IOD events prior to anthropogenic climate change that gives context to the intensification of positive IOD events since the 1960s.

246

Drivers of prolonged expansion and contraction periods of the Indo-Pacific tropical rain belt over the last millennium Ummenhofer, Caroline C.1, Denniston, Rhawn F.2

Presenting author’s e-mail: [email protected]

1Woods Hole Oceanographic Institution, Woods Hole, MA, USA 2Cornell College, Mount Vernon, IA, USA

Session 3.13 – February 8, 2018, 1200-1215

Using state-of-the-art climate model simulations conducted as part of the Last Millennium Ensemble with the Community Earth System Model (CESM), we evaluate variations in the width of the Indo- Pacific tropical rain belt (TRB) over the pre-Industrial portion of the last millennium (AD 850-1850). The TRB marks the high-rainfall region in the tropics traversed by the seasonal migration of the intertropical convergence zone. In particular, changes in the position of the northward and southward edges of the TRB can have considerable impacts on natural and human systems. The climate model results complement a recent reconstruction of late Holocene variability of the Indo-Pacific TRB, derived from precisely-dated stalagmites from cave KNI-51, north-central Australia, at the southern edge of the TRB and stalagmites from Dongge Cave, southern China, at the northern edge of the TRB.

In the model simulations and proxy-based records, we identify multi-decadal to centennial periods when the Indo-Pacific TRB expanded/contracted during the last millennium, as indicated by symmetric weakening and strengthening of summer monsoons in the Northern and Southern Hemispheres of the Indo-Pacific (the East Asian summer monsoon in China and Australian summer monsoon in northern Australia). These prolonged periods of an expanded (contracted) TRB coincide with characteristic patterns of Indo-Pacific sea surface temperatures reminiscent of negative (positive) phases of the Interdecadal Pacific Oscillation and corresponding changes in atmospheric moisture transport in the Austral-Asian sector. Comparison of prolonged expansion/contraction periods of the TRB in individual ensemble members of the model simulations and the multi-ensemble mean allows us to quantify the relative contributions from internal variability and external forcing. Synthesis with terrestrial (stalagmites) and marine (coral) paleo proxy records provides a test of the roles played by internal variability and external forcing for specific TRB expansion/contraction periods observed in the paleoclimate record of the last millennium.

247

3.14 Data homogenisation and other statistical challenges in climatology Testing for collective significance of temperature trends Huth, Radan1,2, Dubrovský, Martin2,3

Presenting author’s e-mail: [email protected]

1Charles University, Prague, Czechia 2Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, Czechia 3Global Change Research Institute, Brno, Czechia

Session 3.14 – February 6, 2018, 0930-0945

A common way of assessing long-term trends in climate elements at individual sites (stations or gridpoints) is to conduct separate local significance tests at each site, without any attempt to evaluate whether the number of individual local tests that are found significant could (or could not) occur by chance at a given significance level. That is, the issue of collective (global, field) significance in the context of testing for climatic trends has been overlooked almost completely. Additionally, insignificant local (station) trends are often ignored in climate change detection studies, which results in a considerable loss of potentially useful information.

In order to avoid this gap, we evaluate several tests for field significance on synthetic datasets, generated by multi-site stochastic generator SPAGETTA (SPatial GEneraTor for Trend Analysis). These tests are based on: (i) counts of locally significant tests, (ii) lowest p-value of all local tests (Walker test), (iii) false discovery rate (generalization of the Walker test); (iv) generalized Mann-Kendall test; and (v) counts of positive and negative trends regardless their local significance (which has been proposed and developed by us). The evaluation is conducted on synthetic data defined on a regular grid with various values of spatial and temporal autocorrelation and for various values of trend, which are all spatially uniform. The sensitivity of results of statistical testing to the length of the series and to the proportion between autocorrelation distance and the density of the station network / grid is assessed.

The tests are then applied to real temperature data in Southern Hemisphere, both station and gridded. The tests of collective significance confirm that temperature trends were positive since the half of the 20th century.

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Investigating Australian temperature distributions using record breaking statistics and quantile regression Jager, Elisa1, Takacs, George1

Presenting author’s e-mail: [email protected]

1University of Wollongong, NSW, Australia

Session 3.14 – February 6, 2018, 0945-1000

There is an established upwards trend in mean temperatures globally and in Australia, but the question of whether temperature distributions are changing is unresolved. Common approaches involve using spatially aggregated or interpolated data which can skew the distribution. The practise of using a climatological reference period systematically exaggerates the growth in variance of a time series, leading to overblown estimates of variability and extreme values (Sippel et al. 2015). Analysing the occurrence of record breaking events can give insight into changes in the distribution. We have analysed record breaking statistics for all 112 stations in the ACORN-SAT database and performed quantile regression. The individual time series for each calendar day was extracted and record breaks for new highs and lows in both the max and min temperatures found. The results of these 365 time series could then be averaged for each station, with most stations producing fewer record breaks than expected over the length of the record when going both forwards and backwards in time along the series. This may be due to long term fluctuations present in the daily series (such as from the solar cycle). The trends in the ratio of observed to expected were also analysed with roughly one quarter of the trends being significant. The preliminary analysis of the trends agrees with the hypothesis of a stationary rising distribution with increasing rates of high max and min records and decreasing rates of low max and min. This work builds on the previous study of Trewin and Vermont 2010 by using a longer time period and adding comparison to theory and agrees with findings on record breaks in aggregated data (Lewis and King 2015). Additionally quantile regression on the data shows some evidence for changing distributions in autumn, but not other seasons.

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A fluctuation in surface temperature in historical context: reassessment and retrospective on the evidence Risbey, James1, Lewandowsky, S2, Cowtan, K3 Oreskes, N, Rahmstorf, S., Jokimaki, A, Foster, G

Presenting author’s e-mail: [email protected]

1CSIRO Oceans & Atmophere, Hobart 2University of Bristol, UK 3University of York, UK

Session 3.14 – February 6, 2018, 1000-1015

Global mean surface temperature (GMST) fluctuates on decadal and longer time scales about the longer-term rise wrought by greenhouse forcing. The most recent fluctuation slower than the long- term rise has been deemed unusual enough to be given its own name; `pause' or `hiatus'. This work examines the statistical evidence for this finding. We take into account the different versions of GMST that existed at different points in time as well as the most recent versions of the data. We assess what is now known about the pause-period, along with what was known as the research unfolded. In the process we analyse the impact of debiasing of the GMST data and of statistical choices for assessing short-term GMST trends.

250

The next-generation ACORN-SAT Australian temperature data set Trewin, Blair1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Australia

Session 3.14 – February 6, 2018, 1015-1030

The next generation of the Australian Climate Observations Reference Network – Surface Air Temperature (ACORN-SAT) data set is due for release in early 2018. The ACORN-SAT data set, first released in 2012, contains daily maximum and minimum temperatures from 1910 to the present and is the major data set underlying the Bureau of Meteorology’s long-term climate analyses, as well as supporting many research applications. The data set contains 112 Australian stations in total, 62 of which have data from the full 1910-2016 period.

In addition to bringing the data set up to date (including transitioning to new stations at a number of locations where the original station has closed since 2012), the new version incorporates recently digitised historical data from a number of locations. There have also been a number of methodological improvements, including running multiple inhomogeneity detection methods in parallel, a more rigorous method for identifying and replacing potentially inhomogeneous reference stations, retaining full data precision in the analysis process, and improved treatment of days with very small diurnal temperature ranges.

The new version of the data set shows slightly stronger warming than the previous version, with mean temperature trends of approximately 0.11°C per decade over the post-1910 period. The main contributors to this are the incorporation of the very warm recent period, and the removal of a rounding bias which had led to some adjustments in the previous version being slightly underestimated. Overall, the datasets shows improved spatial consistency in patterns of variability and change, suggesting that inhomogeneities at stations have been more effectively removed.

Warming of temperature extremes has been generally consistent with warming in the means, with more warm extremes and fewer cool extremes, although there are some exceptions to this in recent decades, particularly in northwestern Australia, and for low minimum temperatures in winter in those parts of southern Australia which have experienced cool-season rainfall decline.

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3.15 Climate – general Precipitation and land-atmosphere feedbacks control the uncertainty in how mid-latitude heat extremes intensify in the future Donat, Markus1, Angélil, Oliver1, Pitman, Andy1

Presenting author’s e-mail: [email protected]

1University of New South Wales, NSW, Australia

Session 3.15 – February 8, 2018, 0930-0945

Extreme heat is expected to intensify in most regions of the world as a consequence of global warming, but the magnitude of heat intensification differs strongly between regions and between different climate models. Some of the regional differences are related to different rates of background warming, but feedbacks can amplify the warming of hot extremes relative to mean temperature warming. Climate model simulations show that in large parts of the Northern Hemisphere mid- latitudes, hot extremes are warming faster than the annual average temperature due to drying soils during summer. Although these regional hotspots of amplified warming of hot extremes are robust across most CMIP5 models, there are large uncertainties regarding the amount of warming.

Here we show that the magnitude by which extremes increase is determined by how strongly summer soil moisture decreases – which in turn is strongly related to seasonal precipitation changes during spring across the different models. An addition, there are substantial inter-model differences in how strongly hot extremes respond to soil moisture and precipitation variability, and models with a stronger response under current climate conditions simulate larger increases in future hot extremes.

While there is currently little potential to reduce the uncertainties around future precipitation changes, we can use observed precipitation – hot temperature relationships as a constraint to identify the models with more realistic land-atmosphere feedbacks on hot extremes. Implementing this constraint within the CMIP5 ensemble reduces the probability of the strongest hot temperature increases and thereby lowers the ensemble mean estimate for increases in hot extremes regionally by up to 1K.

252

Interdecadal Pacific Oscillation influences the timing of an ice-free Arctic Ocean Screen, James1

Presenting author’s e-mail: [email protected]

1University of Exeter, Devon, United Kingdom

Session 3.15 – February 8, 2018, 0945-1000

One of the most visible and iconic aspects of recent climate change is the dramatic loss of Arctic sea- ice, which is having profound implications on the environment, ecosystems and human inhabitants of this region and beyond. The concept of an ‘ice-free Arctic’ has captured scientific attention and public imagination. Scientists commonly define this as when the Arctic first becomes ice-free at the end of summer; specifically, the first year when the average September sea-ice extent falls below 1 million km2. Without efforts to slow manmade global warming, an ice-free Arctic would likely occur in summer by the middle of this century. The precise timing of an ice-free Arctic will depend however, on both the magnitude of future human-induced global warming and upon the magnitude and phasing of internal climate variability. This talk will present results from a large initial condition ensemble of global climate model simulations. Each ensemble member has a different realization of internal variability superimposed on the underlying externally forced response. Ensemble members that transition more quickly from present-day to ice-free conditions tend to be those that over the same time period are transitioning from negative to neutral/positive conditions of the Inter-decadal Pacific Oscillation (IPO). The phase of the IPO can shift the projected timing of first ice-free conditions by around 5-10 years. Ensemble members that depict the IPO- phase in the 10-year period ending 2016 tend to transition toward IPO+ in the following decades, which accelerates the loss of ice and leads to an earlier projection of ice-free conditions. This suggests that future projections of Arctic sea ice can be constrained by the observed IPO phase. If the real world IPO continues to transition towards it’s positive phase, away from IPO- in the recent past, this may hasten the emergence of ice-free summers in the Arctic.

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Compelling evidence for a very limited role of internal climate variability on global warming Haustein, Karsten1, Venema, Victor2, Cowtan, Kevin3, Hausfather, Zeke4,5, Way, Robert G.6, Otto, Friederike E.L.1, Schurer, Andrew7

Presenting author’s e-mail: [email protected]

1Environmental Change Institute, University of Oxford, Oxford, UK 2Department of Meteorology, University of Bonn, Germany 3Department of Chemistry, University of York, York, UK 4Berkeley Earth, Berkeley, CA, USA 5University of California Berkeley, Berkeley, CA, USA 6Department of Geography, University of Ottawa, Ottawa, Canada 7School of Geosciences, University of Edinburgh, UK

Session 3.15 – February 8, 2018, 1000-1015

The early 20th century warming (EW; 1910-1940) and the mid-20th century cooling (MC; 1950-1980) have been linked to both internal variability of the climate system and external radiative forcing variations. The degree to which either of the two factors contributed to EW and MC is still debated. Multidecadal variability in the North Atlantic (Atlantic Multidecadal Variability; AMV) has often been used as explanatory variable for changes in GMST.

Using a two-box impulse response model, here we demonstrate that the AMV did not drive observed changes in GMST after 1850 A.D. Instead, 98-99% of the global low-frequency variability is explained by variations in external radiative forcing. High co-variability between AMV and anthropogenic aerosol forcing (AAF) is identified as the main source for mis-attribution in many earlier studies. We provide robust evidence that if (1) the heterogeneous nature of AAF is taken into account, (2) appropriate fast and slow response time estimates are applied, and (3) the model is initialised before at least 1800 A.D., the inter-hemispheric as well as the land-ocean temperature evolution can be reproduced with high accuracy (95-98% explained variability across the analysed time series), including the EW and MC period.

The small fraction of remaining unexplained low-frequency variability is attributable to biases in the early part of the instrumental SST record as demonstrated with a neat method that allows to construct a global SST proxy based on coastal and island station data as well as coastal SST data. Most notably, the warm SST bias during WWII can be reliably eliminated. We show that interannual and decadal higher frequency variations in GMST are almost completely described by ENSO modulations. In this context, we are also able to demonstrate that multidecadal variability associated with the Pacific Decadal Variability index (PDV) has - while detectable - no bearing on the high fraction of explained low-frequency variability.

Extending our analysis back in time until 1500 A.D., we conclude that internally generated low- frequency modes of variability are an unlikely factor in the Northern Hemisphere (NH) temperature evolution over the course of the last 200-500 years. Omitting the period of strong volcanic activity between 1815-1840, we find that CMIP5 GCMs as well as our response model underestimate the observed temperature trends during the EW period. Even current warming levels are marginally biased warm. We therefore argue that model initialisation in 1850 is not ideal considering the planetary energy imbalance at this point.

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Our associated best estimate for the transient climate response (TCR) is 1.6K (0.9-2.2K; 10-90th percentile). Based on an accompanying sensitivity analysis, we recommend not to rely on observationally based estimates to infer the equilibrium climate sensitivity (ECS) as it is more likely a rather time-dependent instantaneous climate sensitivity (ICS).

255

Climate sensitivity revisited Ayers, Greg1

Presenting author’s e-mail: [email protected]

1Visiting Scientist Emeritus, Bureau of Meteorology, Melbourne, VIC, Australia

Session 3.15 – February 8, 2018, 1015-1030

The energy balance model of Gregory et al. (2002) sitting behind many published estimates of Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR) to anthropogenic forcing uses four parameters for calculation of ECS and three for TCR. Both require a value for increase in global mean surface air temperature over a period (ΔT), the increment in forcing over that time (ΔF), and the radiative forcing from doubling in CO2 concentration (F2xCO2). To calculate ECS a value for observed global heating rate (ΔQ) is also required. Although best estimates for these parameters were given in the IPCC’s 5th Assessment, the AR5 authors decided not to provide best estimates for ECS and TCR, quoting only broad uncertainty ranges of 1.5-4.5K and 1.0-2.5K respectively.

Here best estimates for ECS and TCR consistent with AR5 values for ΔF and F2xCO2 are developed. A well-known heuristic model was modified and applied to seven global air temperature datasets to extract temperature change due to anthropogenic forcing free from confounding variability from volcanism, cycles in solar irradiance and internal climate variability. The seven estimates of ECS and TCR were remarkably similar despite large differences in time-base of the datasets analysed, yielding mean values of 2.37±0.13 K and 1.58±0.09 K respectively based on the AR5 best estimates for ΔF, F2xCO2 with ΔQ from Wiffjels et al. (2016). Should the latter values be refined in the future, these ECS and TCR best estimates can be scaled accordingly. Similar analysis of 45 CMIP5 20th Century simulations yielded mean ECS and TCR values 17% higher than from the observational datasets. Possible explanations for this small difference could be a systematic cool bias in the observational datasets, or that the models on average have an elevated positive response to anthropogenic forcing compensating for an elevated negative response to volcanic forcing.

256

3.16 Historical climatology in the Southern Hemisphere An Australian history of anthropogenic climate change Morgan, Ruth1

Presenting author’s e-mail: [email protected]

1Monash University, Victoria, Australia

Session 3.16 – February 6, 2018, 1430-1445

Focusing particularly on Oceania or the Pacific Islands, as well as Australia and New Zealand, this paper reviews the concept of the Anthropocene through the environmental histories and histories of science of the Southern Hemisphere. Bringing together the diverse ecological and human histories of this vast region highlights the strikingly different ways that the Global South and Global North have contributed to and experienced planetary change since 1945. Until the 1970s, the southern hemisphere remained largely absent from scientific considerations of the planetary impacts of human activity. Although the International Geophysical Year had been a boon for Antarctic exploration, the Pacific and Indian Oceans remained ‘embarrassingly unknown’ south of the equator nearly a decade later. This paper examines the role of Australian climatologists and meteorologists in advancing the state of knowledge about the causes and mechanisms of climatic change and variability in the Southern Hemisphere from the mid-1970s to the 1990s. It contends that Australia’s geopolitical position and environmental sensitivity to climatic change encouraged Australian scientists and policymakers to take a leading role in the study of global environmental change.

257

Increasing Australia’s tide gauge records through data digitisation McInnes, Kathleen1, O’Grady, Julian1, Trenham, Claire1, Hague, Ben2, Hoeke, Ron1,Mitchell, Bill3

Presenting author’s e-mail: [email protected]

1CSIRO Climate Science Centre, Aspendale, Australia 2Bureau of Meteorology, Australia 3Bureau of Meteorology, Adelaide

Session 3.16 – February 6, 2018, 1445-1500

Extreme sea level events (e.g. storm surges) cause flooding, erosion and salinization of the coastal margin. Understanding how they are changing is important not only for coastal management and planning but also to build confidence in projected changes to sea level extremes and the weather systems that cause them. High quality tide gauge records of sufficient duration, temporal resolution and spatial coverage are required to understand the role of interannual variability and extremes at the regional scale. Australia’s extensive coastline extends from the tropics to the mid-latitudes and is influenced by various meteorological and climatological drivers that influence sea levels and extremes on interannual time scales (McInnes et al, 2016). However, in Australia, fairly complete digital records of quality-controlled, hourly sea level observations are available at only two locations; Fremantle (from 1880) on the west coast in Perth and Fort Denison (from 1912) on the east coast in Sydney. Most other digital tide gauge records in Australia commenced in the mid-1960’s or later. However, tidal records mainly in the form of marigrams are available at a number of locations along Australia’s southern and tropical east coast and offer the opportunity to increase the number and diversity of coastal locations where long, quality-controlled hourly sea level observations are available for research of past changes in sea level and extremes (McInnes et al, 2016). Here we will report on progress towards digitising the first of these records, located at Williamstown in Melbourne on Australia’s south coast. At this location marigrams are available from 1875 through to 1965 (after which time the digital record commences). In addition, a near-complete set of tide registers (books that record the daily high and low waters) is available from 1872). Information on the data sources will be provided. A preliminary analysis of extreme sea levels in the digitised records to date and some notable extreme sea level events that have been recorded in these records will also be presented and discussed.

Reference:

McInnes, K.L., White, C.J., Haigh, I.D., Hemer, M.A., Hoeke, R.K., Holbrook, N.J., Kiem, A.S., Oliver, E.C.J., Ranasinghe, R., Walsh, K.J.E., Westra, S. and Cox, R.2016: Natural hazards in Australia: sea level and coastal extremes. Climatic Change. DOI: 10.1007/s10584-016-1647-8

258

Learning from notorious maritime storms of the late 1800s Browning, Stuart1, Goodwin, Ian1

Presenting author’s e-mail: [email protected]

1Macquarie University, NSW, Australia

Session 3.16 – February 6, 2018, 1500-1515

Tasman Sea maritime history tells of extreme East Coast Low (ECL) events responsible for the loss of dozens of ships and hundreds of lives, as well as costal impacts such as erosion and inundation. The late 1800’s saw many such extreme events. Our understanding of these storms is drawn mostly from documentary evidence. The availability of the Twentieth Century Reanalysis (20CRv2c) has improved understanding of ECL activity during the late 1800’s, however uncertainty in the reanalysis complicates resolving storm tracks for individual events. It is therefore not well understood how these notorious events compare to our current understanding of ECL development, magnitude and risk, which is based events observed in recent decades, such as the Pasha Bulka storm.

In this study we combine documentary records with automated cyclone detection and tracking algorithms applied to the 20CRv2c ensemble members to provide a best estimate of the storm tracks, wind fields, and mean sea level pressure fields for 5 extreme ECLs occurring in the late 1800’s: The Dunbar Storm of 1857, The Catherine Hill Gale of 1867, The St Magnus Gale of 1875, The Dandenong Gale of 1876, and The Maitland Gale of 1898. Each of these events caused widespread impacts along Australia’s eastern seaboard. Resolving storm tracks and large scale environments in which these events developed helps to improve our understanding of the ECL storm family and overall perception of ECL risk under past, current, and future climate change scenarios. This study also provides additional detail to our historical understanding of Eastern Australia’s maritime heritage.

259

Climate data rescue activities at Météo-France in the Southern Hemisphere Peltier, Alexandre1, Jourdain, Sylvie2, Tardy, Marc3, Bonnardot, François4

Presenting author’s e-mail: [email protected]

1Météo-France, New-Caledonia, France 2Météo-France, Toulouse, France 3Météo-France, Tahiti, France 4Météo-France, Reunion Island, France

Session 3.16 – February 6, 2018, 1515-1530

Météo-France, as France’s national meteorological service, contributes to the recovery of historical instrumental climate data (surface and upper-air) for all the French territories and for some former French colonies. At Météo-France, the national climate data rescue program comprises organising, cataloguing, imaging, digitising and applying quality control tools according the best practices recommended by WMO.

In the last few years, a particular focus has been on inventorying all the Météo-France climate archival holdings, including New-Caledonia, French Polynesia, Wallis-et-Futuna and Reunion Island. At the same time, efforts have been made in imaging of records from New-Caledonia, Wallis-et-Futuna and French Polynesia covering 1910-1970.

Furthermore, the National Archives of France, located near Paris, houses archives of historical handwritten meteorological observations for all the French territories in the southern hemisphere covering 1864-1931. Major efforts have been undertaken to recover climate data from these territories with the Access to Climate Archives (AAA) project from 2012 to 2016. Priority was given to cataloguing and imaging all climate monthly tables. Now, several dedicated actions of digitisation and quality-control are in progress to recover the long-term series of sub-daily data of the French colonial hospitals (Nouméa and Tahiti).

In addition, Météo-France is currently involved in a new multi-year initiative on recovery of historical data from Madagascar for the periods 1864-1918 and 1947-1961, from original sources stored at the National Archives.

Besides, Météo-France is involved in the Access to French Climate Records (ARClim) project aiming to build the numerical library of French climate archives using a record management system. The numerical library will enables the research of climate records (hardcopy and digital images) and allow the visualisation of the images.

260

Recovering historic Southern Ocean climate data using ships’ logbooks and citizen science Pearce, Petra1, Lorrey, Andrew1, Wilkinson, Clive2, Allan, Rob3, Brohan, Philip3, Compo, Gil4

Presenting author’s e-mail: [email protected]

1National Institute of Water and Atmospheric Research, Auckland, New Zealand, 2RECLAIM, University of East Anglia, United Kingdom, 3UK Met Office, Exeter, United Kingdom, 4NOAA-CIRES, University of Boulder, Colorado, United States

Session 3.16 – February 6, 2018, 1530-1545

Ships’ logbooks are a significant resource of historic climate data where land-based observations are sparse. During the 19th and 20th centuries, many whaling, trade, exploration and migrant ships took regimented weather observations during their voyages through the Southern mid-to-high latitudes. Due to the lack of historic instrumental data in this region, the Deep South National Science Challenge (DSC), supported by the New Zealand Government, has chosen to support recovery and digitisation of historic data contained within ships’ logbooks.

The global Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative facilitates the rescue and digitization of historic weather observations. ACRE Antarctica has been set up to identify, rescue and digitize historic observations that can augment modern reanalyses (daily weather reconstructions) which will help to validate and test the New Zealand Earth System Model. ACRE Antarctica has a primary goal of extending spatiotemporal coverage for a domain covering south of 40°S and between 130°E and 30°W (Tasmania to east of the Drake Passage) for the period 1850-1960. This effort will double the present number of observations in the 20th Century Reanalysis for this domain and time period.

Over 130,000 images of ships’ logbooks covering voyages to the Southern Ocean and Southwest Pacific have been recovered from UK and European archives so far, and data keying has begun. The project intends to recover surface pressure, sea ice, air temperature and sea surface temperature data along with other essential climate variables. ACRE Antarctica will feed logbook images into the OldWeather citizen science platform to assist with the monumental task of data keying. We expect that improving data coverage across the Southern Ocean will clarify long-term weather changes that regularly impact New Zealand and evaluate inter-annual to multi-decadal climate variability and atmospheric processes connected to several climate modes.

261

Theme 4: Weather 4.1 A session in honour of Professor Ian H. Simmonds Atmospheric transport modelling and applications Law, Rachel1, Noone, David2, Rayner, Peter3, Pak, Bernard1, Dargaville, Roger4, Josephine Brown5

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Vic, Australia 2Oregon State University, OR, USA 3University of Melbourne, Vic, Australia 4Monash University, Vic, Australia 5Bureau of Meteorology, Vic, Australia

Session 4.1 – February 6, 2018, 1430-1445

The atmosphere is dynamic and long-lived atmospheric constituents are transported and mixed between hemispheres and vertically. Modelling that transport contributes to interpreting a range of atmospheric composition observations, allowing a number of research questions to be addressed. Here we review the development of atmospheric transport modelling at Melbourne University under the supervision of Ian Simmonds, and its ongoing application to greenhouse gases and water isotopes through the careers of those involved. For greenhouse gases, atmospheric transport provides the link between, primarily, surface fluxes of those gases and their observations in the atmosphere, such as those measured at Cape Grim, Tasmania. Much research has focussed on the inverse problem where the fluxes are inferred from the atmospheric measurements to provide a ‘top-down’ constraint on carbon and methane budgets that are otherwise constructed from ‘bottom-up’ inventories or process models. Modelling stable water isotopes provides insight into many atmospheric processes related to atmospheric transport and the hydrologic cycle. One example is in better determining the transport of water to Antarctica with implications for the interpretation of ice-core measurements. Another is that water isotope modelling can be used to assist the interpretation of tropical proxies such as corals used to reconstruct past tropical climate variability e.g. ENSO.

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From one of the first objective cyclone tracking schemes to a unique frontal identification method Rudeva, Irina1, Simmonds, Ian1, Keay, Kevin2

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia 2Bureau of Meteorology, VIC, Australia

Session 4.1 – February 6, 2018, 1445-1500

The cyclone tracking scheme was developed at the University of Melbourne under Professor Ian Simmonds supervision more than 20 years ago. Since then it has been extensively used by the local and international community for identification and tracking of both cyclones and anticyclones. Interestingly, the scheme works well with modern high resolution data though at the time of its development even 5-degree resolution was barely available. In a comparison with other fourteen tracking algorithms (Neu et al., 2014), cyclone tracking scheme developed at the University of Melbourne performs well even compared to the latest algorithms, including the one used in weather forecasting practice.

Ian Simmonds was also the mastermind of one of the first objective frontal identification scheme developed a few years ago at the University of Melbourne. Ian Simmonds offered a novel and somewhat debatable approach to frontal identification based on a wind shift. The method is particularly suited for the detection of strongly elongated, meridionally oriented moving fronts, which typically extend far equatorward from the cyclone centre. While this approach might not be accepted by some of the scientists, a comparison with other methods, that use a more conventional Thermal front Parameter (TFP), shows good results, which is a significant achievement given its computational simplicity. Even more so, in contrast to TFP methods that often show artificial fronts in the subtropical regions or high latitudes (e.g., in the areas of large thermal and/or moisture gradients), Ian Simmonds’s method shows more robust results.

263

How much does atmospheric frontal rainfall in Australia and New Zealand depend on SST frontal strength in the Indian and Southern Oceans? Parfitt, Rhys1, Ummenhofer, Caroline1

Presenting author’s e-mail: [email protected]

1Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Session 4.1 – February 6, 2018, 1500-1515

It has been shown in recent years that the mean atmospheric state (vertical motion, mean sea-level pressure, precipitation etc.) over mid-latitude regions of strong sea-surface temperature gradients is a residual of overlying synoptic activity. Furthermore, it has been hypothesized that the key interaction that determines the local and basin-scale ocean-to-atmosphere feedback takes place specifically between the ocean fronts and the individual atmospheric fronts embedded in these synoptic systems. In this talk we examine this interaction in the Indian and Southern Oceans, with a focus on how its inter-annual variability affects wintertime frontal rainfall in Southern Australia and New Zealand. As a result, we discuss why the impact of these oceans on many extreme rainfall events can only be properly represented in general circulation models and reanalysis datasets with a coupled resolution of at least 25km.

264

Recent trends and variability in global cyclones and anticyclones Pepler, Acacia1, Hope, Pandora1, Dowdy, Andrew1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, NSW, Australia

Session 4.1 – February 6, 2018, 1515-1530

Recent decades have seen a strengthening of the subtropical ridge, which has been associated with decreasing cool-season rainfall in parts of southern Australia. This could be considered a result of changes in the mean location and intensity of both slow-moving high pressure systems and transient low pressure systems. However, while several studies have assessed global changes in cyclone activity, relatively few have assessed changes in either the frequency or characteristics of anticyclones. In this study, we apply the University of Melbourne tracking scheme to track both cyclones and anticyclones across a range of reanalyses, including the 20th Century Reanalysis Ensemble. This provides a new look at long-term change and variability in global cyclone and anticyclone activity, with a focus on recent trends in Southern Australia. Preliminary results show an increase in both the frequency and central pressure of anticyclones has been observed over southern Australia since the 1970s. However, there has been no change in the average latitude of Australian anticyclones and an increase in the average longitudinal movement, contrary to expectations.

265

An analysis of Southern Hemisphere circulation over the last millennium Noone, David1

Presenting author’s e-mail: [email protected]

1Oregon State University, Oregon, USA

Session 4.1 – February 6, 2018, 1645-1700

The sparsity of long term meteorological observations in the Southern Hemisphere has hampered assessment of trends in atmospheric circulation. While the decades-long satellite record has helped provide spatial context, temporal extension of the instrumental record requires use of so-called “proxy” information. Previous examples have demonstrated the utility of proxy data to characterize both qualitative and quantitative aspects of Southern Hemisphere climate, yet there remains criticism that proxy approaches fail to properly account for physically-based spatial and temporal constraints that well-understood atmospheric circulation patterns impose. On the other hand, atmosphere and ocean general circulation models can provide insight into the circulation structure (e.g., Semi-Annual Oscillation, Annual Mode, and storm activity), albeit at the expense of being only an approximate representation of the Earth’s true circulation. Pioneering work on understanding Southern Hemisphere climate required refinement of comprehensive climate models to better account for processes that play significant roles in the Southern Hemisphere; including treatment of sea ice, arid landscapes and the general circulation itself. Here we combine the benefits of comprehensive modelling with the long observational constraints offered by the paleoclimate datasets to provide a millennial-length analysis of the Southern Hemisphere circulation. The analysis is facilitated by model developments to directly simulate “proxy” quantities (isotope ratios of coral, ice cores and tree ring width), which enables paleoclimate data to be quantitatively blended with model solutions via data assimilation. Long term trends and variability in the mid-latitude jet, cyclone activity and sea ice state are obtained. Results are contrasted with earlier evaluations that were based on either free-running general circulation model simulations or more limited observational datasets. The findings both provide new insight to the climate history of the Southern Hemisphere and offer a platform from which to highlight the benefits that emerge from decades-long investment in advancing several related branches of meteorology.

266

Variability in planetary wave activity over the 20th century Lynch, Amanda1,2, Zsom, Andras3

Presenting author’s e-mail: [email protected]

1Institute at Brown for Environment and Society, Brown University, RI, USA 2Dept of Earth, Environmental and Planetary Sciences, Brown University, RI, USA 3Computing and Information Services, Brown University, RI, USA

Session 4.1 – February 6, 2018, 1700-1715

The contrasting geographies of the Southern and Northern hemispheres play a significant role in the observed Rossby wave regimes. In addition to differences in the continental distribution and the location of major north-south mountain chains, the mean equator-to-pole temperature difference is significantly larger in the Southern Hemisphere (around 70 K) than in the Northern Hemisphere (around 40 K). As such, the evolving nature of these wave regimes have been extensively studies in climate models and re-analyses. Planetary wave amplitude is a challenging measurement compared to parameters such as wave propagation speed, jet strength and location, and wavenumber. In this study, the evolution of planetary wave amplitudes over the 20th Century are analyzed using a novel implementation of the quasi-geostrophic wave activity parameter. The trajectories of change are distinctive between the hemispheres and can be linked to sea ice properties.

267

It’s just not cricket! Screen, James1

Presenting author’s e-mail: [email protected]

1University of Exeter, Devon, United Kingdom

Session 4.1 – February 6, 2018, 1715-1730

In mid-2009, as the England cricket team were beginning their 2-1 Ashes series victory, I started a post-doc with Prof Ian Simmonds (aka “Simmo”). We have enjoyed a fruitful collaboration thereafter, despite me being a “Pom” and three consecutive Ashes victories for the English during my post-doc years (for the first time in my lifetime; albeit not in Simmo’s). In this talk I will revisit some of the research highlights – and the stories behind them - stemming from my collaboration with Simmo, focusing on our work on Arctic climate change. This will include the “ripper” of a plot that led to our first publication success in Nature in 2010 (coincidently, the year of England’s historic 3-1 Ashes victory on Australian soil) and Simmo’s highest cited paper; the paper with a title which (seemingly) took longer to write than the manuscript; a brief foray into Arctic cyclones (to keep Simmo happy; this was supposed to be the focus of the whole post-doc) and much more in-between. Did I mention the cricket?

268

If that’s correct, we'll win a Nobel Prize! Being healthily sceptical with common or garden variety climate indices Watkins, Andrew B.1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Melbourne, Vic, Australia

Session 4.1 – February 6, 2018, 1730-1745

Professor Ian H. Simmonds taught his students many things, but surprisingly to some, the best lessons didn’t actually come from the pages of Holton (1972). He actively educated his students with natural curiosity, healthy scepticism, a willingness to look at something from many angles, simple objectivity, and placing knowledge into the context of the wider world.

In 2015 an El Niño emerged that was touted as being one of the most anticipated, accurately observed and strongest ENSO events of all time. It all seemed quite cut and dried. But if it was so strong, why did the atmosphere respond so weakly relative to past events? If it was so well observed, why did different agencies have very different Nino index values? And if you took away the climate change warming signal, was it really that significant? At least some of these questions may be answered by homogenisation of past satellite observations and differences in base periods.

Then in winter 2017, a significant dry pattern emerged over Australia that had some characteristics of a positive Indian Ocean Dipole event, but clearly no event was in place. However a west-east gradient in sea surface temperatures across the Indian Ocean did suggest an IOD-like (but southwards shifted) pattern may indeed have been having a significant influence upon Australia's climate.

Just accepting simple climate indices as being set in stone may in fact be compromising our understanding of climate variability and may, and for operational and research climate scientists, have quite significant ramifications. We need to think carefully and clearly about the data we use, and how that data is changing. As Simmo would say, assuming indices won't change is a trap for young players.

269

4.2 High impact weather in research and operations South East Queensland hazard analysis and verification testbed – operations and preliminary results Soderholm, Joshua1, McGowan, Hamish1, Mason, Matthew1, Dowdy, Andrew2, Wedd, Tony2, Protat, Alain2, Richter, Harald2

Presenting author’s e-mail: [email protected]

1The University of Queensland, QLD, Australia 2Australian Bureau of Meteorology, VIC, Australia

Session 4.2 – February 8, 2018, 0930-0945

Severe weather hazards result in estimated global losses of $250 to $300 billion USD annually, with increasing exposure an ongoing challenge (UN Office for Disaster Risk Reduction 2015). Within Australia, individual thunderstorm events have resulted in losses exceeding $1 billion AUD in the space of minutes. Weather radar is instrumental for effectively detecting and warning for storm related hazards, however, the underlying algorithms lack calibration or verification for Australian events. Furthermore, the current dual-polarised upgrade of four BoM capital city radars provides an opportunity to improve upon existing thunderstorm hazard detection.

The following paper presents the South East Queensland Hazard Analysis and Verification Testbed (SEQ-HAVT). This project is an industry, university and government supported effort to improve severe wind and hail detection, and fast-track the application of dual-polarised techniques for operational prediction. The testbed will be utilised by a multi-year field campaign and community science initiative to collect datasets required for calibration and verification of radar-based hazard algorithms. A summary of the observational strategy and preliminary analysis from the first year will be presented. Alongside the field program, detection algorithms will also be applied to improve the skill of radar- derived and environmental thunderstorm climatologies, supporting the development of fine-scale hazard risk modelling. Initial work towards a national radar-derived climatology will be presented. The roadmap for the SEQ-HAVT project will also be discussed, including applications for industry and government end-users to improve hazard related services.

270

Simulated changes in supercell thunderstorms crossing a sea breeze front Hartigan, Joshua1, Lamichhane, Bishnu1, Soderholm, Joshua2, Warren, Robert3

Presenting author’s e-mail: [email protected]

1The University of Newcastle, NSW, Australia 2The University of Queensland, QLD, Australia 3Monash University, VIC, Australia

Session 4.2 – February 8, 2018, 0945-1000

The South-East Queensland region is frequently impacted by large hail and damaging winds associated with severe convective storms such as the Brisbane hailstorm event of 27 November 2014 and the “Gap” storm of 16 November 2008. These events have presented a significant challenge for forecasting due to their development in seemingly marginal environments. Previous work has suggested that the sea breeze front may be a key mechanism behind the intensification of pre-existing convective storms that have developed in a marginal environment. Despite the high coastal population of Australia and in many countries around the world, the effects of the sea breeze airmass on severe convective weather remain uncertain.

It is well known that boundaries are important mechanisms behind the development of convective storms. However, previous studies have found that convective storms weaken as they cross a boundary in the direction of cool air. This is the opposite of what appears to happen in South-East Queensland. In this study, we have utilised base-state substitution (BSS) – a method for introducing environmental heterogeneities such as sea breeze fronts into the numerical model, CM1. This has allowed the development of high-resolution idealised simulations to determine if the enhanced low- level shear and moisture associated with the sea breeze front causes an increase in the strength and longevity of pre-existing convective storms. A focus is placed upon storms which develop in the low shear, high CAPE environment frequent to the South-East Queensland region.

271

Subtropical heat waves in the Brisbane-region of Australia Reeder, Michael1, Parker, Tess2, Quinting, Julian1

Presenting author’s e-mail: [email protected]

1Monash University, Victoria, Australia 2University of Oxford, UK

Session 4.2 – February 8, 2018, 1000-1015

The synoptic structure and evolution of summer (December – February) heat waves in the Brisbane region is investigated through composite and trajectory analyses. Heat waves in the region fall into two groups: those associated with a mean upper-level anticyclonic potential vorticity (PV) anomaly centred over the south of the continent (hereafter called anticyclonic heat waves), and those associated with an isolated upper-level cyclonic PV anomaly over the south of the continent (hereafter called cyclonic heat waves). Surprisingly, neither case is associated with a significant anticyclonic anomaly in the region of the heat wave. In the anticyclonic case, the upper PV anomaly induces an easterly component in the low-level winds in the region of the heat wave, whereas in the cyclonic case a westerly component is induced at low levels.

Trajectories are started close to the surface near Brisbane and integrated backwards in time. In the anticyclonic case, the air parcels lie predominantly offshore over the Tasman Sea before progressing onshore, turning anticyclonically, and entering the region of the heat wave from the north east. These air parcels are only weakly heated through diabatic processes (2 - 3 K in the composite mean), with the low-level warming due mostly to subsidence and adiabatic compression. Nonetheless, because of their origin over the Tasman Sea, these air parcels are very moist (almost 15 g/kg in the composite mean). In contrast, in the cyclonic case the trajectories circulate cyclonically around the low-level trough south of Brisbane and enter the region of the heat wave from the south west. These trajectories are heated strongly through surface sensible heating over the continent (around 8 K in the composite mean).

272

Bayesian statistical approach for developing a convective windstorm climatology of Australia Spassiani, Alessio1, Mason, Matthew1, Krupar III, Richard J.2

Presenting author’s e-mail: [email protected]

1University of Queensland, QLD, Australia 2University of Maryland, MD, United States of America

Session 4.2 – February 8, 2018, 1015-1030

A climatological analysis is necessary when trying to develop a stochastic model that simulates an extended period of convective windstorm activity across Australia. Unfortunately, the Bureau of Meteorology’s Severe Storm Archive (SSA) lacks completeness because of biases such as differences in population density and reporting practices. To facilitate the development of a convective windstorm climatology the coupling of observational and global reanalysis data is used to determine the probability of severe wind events occurring in different parts of Australia. Severe weather parameters (e.g. CAPE, 0-6km wind shear) have proven useful for weather forecasters to estimate the likelihood of severe weather based on large-scale climatic conditions. These parameters have also been shown to either complement or replace poor observational records of severe weather events (including extreme wind gusts) by climate researchers.

We show here that a hierarchical Bayesian model, considering population density and severe weather indices can reasonably correct for such biases in SSA event counts. This model can also consider the spatiotemporal variability of the underlying factors in severe weather formation by tailoring the parameters used for specific regions. In addition, the hierarchical structure of the Bayesian model allows us to determine the probability of the severe weather event being either a severe wind, rain, or hail event. By utilizing systematic detection algorithms to examine the occurrence of synoptic features in reanalysis data and lightning stroke data to detect the occurrence of convective events, it is also possible to determine the probability of the severe weather event being the result of a synoptic or convective weather phenomena.

273

New developments in the Bureau’s thunderstorm prediction system – Calibrated Thunder Richter, Harald1, Collecutt, G.2, Treloar, A.3

Presenting author’s e-mail: [email protected]

1Australian Bureau of Meteorology, Melbourne, Australia 2Australian Bureau of Meteorology, Brisbane, Australia 3Australian Bureau of Meteorology, Sydney, Australia

Session 4.2 – February 8, 2018, 1100-1115

There is clearly an increasing need by many users of weather information to extract thunderstorm information from the output of numerical weather prediction models (NWP), but ‘raw’ NWP output fields are difficult to interpret in view of estimating the likelihood of thunderstorms. Late in 2016 a post-processing package, Calibrated Thunder (CT), went operational at the Australian Bureau of Meteorology. It produces uncalibrated and calibrated probabilities of cloud-to-ground lightning strikes in 3-hourly intervals on a 40 km x 40 km grid over Australia out to 2 days. NWP inputs are sourced from a 5-member lag ensemble of the ACCESS-R model which produces output on a ~12.5 km grid over Australia.

Operational demands have led to the development of two significant extensions to the original CT system. First, the Graphical Forecast Editor, the Bureau’s primary forecast production system, requires thunder probabilities up to eight days in advance. To achieve such a lead time, CT has been duplicated to run off input from the second release of the global ACCESS model (ACCESS-G2) with model fields written to a grid with ~24 km spacing. We will describe the adapted CT system setup and show how the CT reliability, accuracy and ability to distinguish between thunder events and non-events evolves with increasing lead time. Early validation over the 5-month 2016/2017 summer period indicate that CT remains sufficiently skillful for useful operational use out to 8 days, but only for afternoon and evening convection. Nocturnal convection is handled less skillfully by the system, and the system loses significant skill by day 4.

Second, the Bureau’s Extreme Weather Desk drafts daily national convective outlooks on a 20 km x 20 km grid. The CT system has also been adapted to produce 24-hour thunder probabilities on this finer grid. The novel derivation of the 24-hour calibrated probabilities and other new system features will be outlined, and verification results presented.

274

Floods in the South Island of New Zealand: the importance of atmospheric rivers Kingston, Daniel1, Lavers, David2, Hannah, David3

Presenting author’s e-mail: [email protected]

1University of Otago, New Zealand 2European Centre for Medium-Range Weather Forecasts, UK 3University of Birmingham, UK

Session 4.2 – February 8, 2018, 1115-1130

Extremely high precipitation occurs in the Southern Alps of New Zealand, associated with both orographic enhancement and synoptic-scale weather processes. Here we investigate the role of atmospheric rivers (ARs) in driving floods in a series of rivers spanning the latitudinal extent of the South Island of New Zealand. Vertically-integrated water vapour and horizontal water vapour transport, and atmospheric circulation, are investigated concurrently with major floods on the Waiau, Matukituki, Waitaki and Clarence Rivers. Analysis of the largest eight annual maximum floods for each river between 1979 and 2012 indicates that the majority are associated with ARs. Geopotential height fields reveal that these ARs are located in slow eastward moving extra-tropical cyclones, but with the cyclone located at different latitudes for each river, and in turn a different pathway and form of the typical ARs that cause floods in each of the rivers. The confirmation of ARs as a contributor to annual maximum floods in each of these rivers, and the subtle but important differences in synoptic-scale features, indicates the need for their further exploration to better understand the causes of South Island hydrometeorological extremes.

275

Simulations of the Black-Saturday Kilmore East Wildfires with the Unified Model Engel, Chermelle B.1, Toivanen, Jussi1, Reeder, Michael J.1, Lane, Todd P.2, Davies, Laura3, Webster, Stuart4, Wales, Scott1

Presenting author’s e-mail: [email protected]

1School of Earth, Atmosphere and Environment, and ARC Centre of Excellence for Climate System Science, Monash University, Clayton, Victoria, Australia 2School of Earth Science, and ARC Centre of Excellence for Climate System Science, The University of Melbourne, Parkville, Victoria, Australia 3Institute of Marine and Antarctic Science, University of Tasmania, Tasmania, Australia 4UK Met Office, Exeter, United Kingdom

Session 4.2 – February 8, 2018, 1130-1145

Wildfires can cause great damage and loss of life and are especially dangerous in those areas where urban communities merge with their rural surroundings. Consequently, the capacity to accurately predict fire behaviour provides clear benefits to fire management, public safety, protection of personal and public assets, and to the occupational health and safety of the fire-fighting personnel. A model for the spread of a wildfire is developed within the UK Met Office Unified model (UM). As a first step, the atmosphere and the fire is coupled in one direction only, meaning the UM simply provides detailed predictions of winds, temperature and humidity for the wildfire model with no feedbacks to the atmosphere from the heating or the moisture and momentum transports by the fire. In the next step, the atmosphere and fire are coupled, allowing the fire to affect the local-scale weather. In these simulations the UM is configured with four nests with horizontal grid spacings of 4 km, 1.5 km, 444 m and 133 m, and the coupled atmosphere-fire model then used to simulate the Kilmore East fire (in southeastern Australia) on Back Saturday (7 February 2009). The degree of agreement between the simulation and the observed fire behavior is excellent. However, such close agreement is achieved only by coupling the fire to the atmosphere and, importantly, by igniting 18 additional fires at the times and places long-range spots were observed to produce new fires. These additional fires merged to produce the Kilmore East fire complex. Without these additional ignitions, the original fire travels about half as far as it should. Likewise, without coupling the burnt area is about half of that observed. These calculations suggest that the behavior and spread of fires like the Kilmore East fire are predictable, but only when spotting is included and the atmosphere and fires are coupled together. Although much of the work reported here is based on simulations of the atmosphere and fire with horizontal grid spacings of 133 m, experiments with coarser grids suggest that, although the details of the fire spread are lost, a grid spacing of 1.5 km may be sufficient to simulate the main features of the fire spread.

276

The rainfall mechanism analysis of Tropical cyclone Oswald(2013) Deng, Difei1, Ritchie, Elizabeth A.1

Presenting author’s e-mail: [email protected]

1School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Canberra, ACT 2600, Australia

Session 4.2 – February 8, 2018, 1145-1200

Tropical Cyclone Oswald (2013) is considered to be one of the highest impact storms to make landfall in northern Australia. It formed in the monsoon trough over the Gulf of Carpentaria, reached a maximum category 1 intensity, and made landfall over the western Cape York Peninsula on 21st January 2013 as a tropical depression. Oswald had little impact on its initial landfall. However, after landfall, it turned southward and moved parallel to the coastline as far south as Tamworth. As it moved southward, Oswald was able to reorganise and intensify even though its circulation was over land, and caused extreme rainfall and catastrophic flooding to the eastern coastal area. As one of the wettest TCs in Australian history, Oswald lasted for more than 8 days over land, evolving from a TC to ex-TC, and then interacting with upper-level trough-jet systems in the mid-latitudes. It produced three maximum rainfall centres, located near Weipa, Townsville and Rock Hampton respectively. In this presentation, the rainfall mechanisms of the three main rainfall centres are investigated using high resolution WRF simulations. The results show that the boundary friction between ocean and land is mostly responsible for the first rainfall center over the Cape York Peninsula. The second rainfall center is a result of the joint effect of the topography along the east coast and the interaction with lower- latitude monsoon systems. The third center is caused by consecutive interactions with two mid- latitude troughs and upper-level jets, which produce favorable dynamical lifting condition for the intensification and enhancement of rainfall.

277

Improved extreme weather hazard prediction and communication through science to operations Sgarbossa, Dean1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 4.2 – February 8, 2018, 1200-1215

The Extreme Weather Desk, embedded within the Bureau of Meteorology’s National Operations Centre, provides a national focus for extreme weather intelligence, and an additional layer of capability to respond to the increasing frequency of high-impact weather across Australia. The provision of extreme weather intelligence to the Bureau’s Regional Forecast Centres, the media, and high-level internal and external stakeholders and decision makers stems from a strong Science to Operations role in evaluating and implementing new science, techniques and guidance to improve processes, products and services.

An end-to-end forecast process for thunderstorm forecasting was trialled by the EWD during the 2016- 2017 Australian Severe Weather Season. Probabilistic forecasts of thunder, large hail, damaging winds, heavy rainfall, tornado and combined severity were provided nationally on a routine basis to demonstrate the process and products of a potential future thunderstorm service. A daily verification product was produced that collated severe thunderstorm reports and observations, and provided an assessment of the convective environment and performance of automated guidance and new diagnostic parameters. Post-season objective verification completed the end-to-end forecast process and identified skill, systematic and individual biases that further refined the forecast process and strategies.

The EWD is also embarking on further work to demonstrate a potential future service that links the daily thunderstorm forecasts and warnings via rapid update short-term forecasts.

Over the past decade, targeted research has advanced the understanding of fire and meteorological processes; but embedding new knowledge and predictive techniques into fire weather forecasts have been slow. The EWD is currently conducting a national trial of advanced fire weather forecast products; the National Fire Outlook, that focusses on processes other than those captured in the standard fire weather service: the potential for dry lightning, significant wind changes, enhanced fire behaviour and deep plume development leading to pyro-convection.

278

Improvements in the detection and prediction of volcanic ash for aviation at the Bureau of Meteorology Lucas, Chris1, Potts, Rod1, Zidikheri, Meelis1, Dare, Richard1, Manickam, Mey1, Wain, Alan1, Crozier, Adele1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 4.2 – February 8, 2018, 1445-1500

Volcanic ash clouds pose a significant hazard to aircraft and can have a major impact on aviation operations. The Bureau of Meteorology’s Darwin Volcanic Ash Advisory Centre (VAAC) provides an important service around the detection and prediction of volcanic ash in the atmosphere to help the aviation industry manage these risks. This service requires both observations, particularly from the Himawari-8 satellite along with the effective use of modelling capability including the Bureau's ACCESS NWP models and the HYSPLIT dispersion model.

The NOAA/NESDIS VOLCAT algorithm is used to process Himawari-8 satellite data and to automatically detect and provide quantitative estimates of ash cloud properties, including cloud top height and mass loading. In the Darwin VAAC region, case studies for several high-level eruptions show that the detections of ash clouds are generally reliable, although there are limitations when deep convection is present or the ash cloud is optically thick. There are uncertainties with the retrievals of cloud top height.

A significant achievement is the creation of the Dispersion Ensemble Prediction System (DEPS) for volcanic ash, a web-based, demand-driven user interface that defines a set of dispersion model simulations that result in an estimate of the probability that ash amounts exceeding pre-defined thresholds are present within the domain. This approach allows for the effects of meteorological uncertainty to be considered in the forecast.

Continuing work on DEPS is centred on adding the effects of source term uncertainty into the probabilistic calculations. The approach here is to combine real-time observations of the volcanic cloud with inverse modelling techniques to optimize the source term; later efforts will focus on optimizing the mass eruption rate of the volcano by considering the quantitative mass loading retrievals from satellite. This will be a step towards providing reliable ash concentration forecasts desired by the aviation industry.

279

Synoptic and sub‐synoptic‐scale features associated with extreme surface gusts during the Adelaide Storm of September 2016 Earl, Nick1, Simmonds, Ian1

Presenting author’s e-mail: [email protected]

1Melbourne University, Vic, Australia

Session 4.2 – February 8, 2018, 1500-1515

Winds are one of the major contributors to deaths, damage and insured losses in Australia. A ‘freak storm’, leaving 1.7 million people without power, hit the state on the 28th September, causing state- wide blackouts. We comprehensively analyse this event and find that the extra-tropical cyclone (ETC) was indeed extreme, deepening more explosively than all but two Adelaide-affecting ETCs over the past 37 years and exhibiting the lowest central pressure. There were a number of very extreme gust- producing features within the storm including a convective line, which caused many of the most extreme gusts and knocked out the state power grid. A dry slot convective cell also contributed to the extremes and this gust causing feature is known to be rare in ETCs over the UK, so warrants further analysis to examine whether this is common extreme gust-producing ETC feature over the Great Australian Bight. The strongest winds recorded throughout the event occurred on the 29th September, and these were associated with the cold conveyer belt wrapped around the low pressure centre. This generated hurricane force winds, with Neptune Island recording a gust of over 120km/h.

280

Probabilistic forecast of cyclone-induced hazards within SPICy project Bonnardot, François1, Quetelard, Hubert1

Presenting author’s e-mail: [email protected]

1Météo-France, La Réunion, France

Session 4.2 – February 8, 2018, 1515-1530

SPICy project aims at tackling the issue of cyclonic coastal and inland floods forecast in the French Overseas. Reunion Island, located in the tropical south-west Indian Ocean, is exposed to cyclone- induced hazards such as devastating winds, torrential rain, marine and river inundations. It is a quite small steep volcanic island with a complex orography. Therefore, the potential coastal impact is tightly related to the track and the intensity evolution of the tropical cyclone (TC) transiting nearby. Although tropical cyclone (TC) track and intensity forecast have been steadily improving for the last decades, a great amount of uncertainty remains. Risk managers or public agencies need both a reliable forecast of the TC evolution and induced impacts and an estimation of the forecast uncertainty.

Within the project, Meteo-France in Reunion Island has developed an original method to generate ensemble scenarios around RSMC’s official track forecast. The method allows modulating both tracks and intensity of the cyclone. A distinct probability is attributed to each scenario.

Given this ensemble of meteorological forecast, wind and pressure fields are generated through meso- scale modeling (Meso-NH model) for each individual scenario using a bogusing method. This high resolution ensemble of wind field can finally be used for (1) generating probabilistic products such as chance of exceeding different wind threshold (2) forcing a wave model and produce probabilistic forecast of oceanic and coastal conditions.

The proposed presentation will present the ensemble generation method and provide some validation results. The tool will be illustrated through historical events.

This work is supported by the French National Research Agency (ANR – 14 – CE03 – 0013). More details on the project are available at http://spicy.brgm.fr.

281

High-Resolution Rainfall and Hydrological Ensemble Forecasts during the passage of Intense Tropical Cyclone Bejisa (2014) over Reunion Island (SWIO) Meister, Julien1, Bousquet, Olivier1, Recouvreur, Romain2, Bielli, Soline1, Barthe, Christelle1, Bonnardot, François3, Lecacheux, Sophie4

Presenting author’s e-mail: [email protected]

1LACy, UMR 8105 (Meteo-France, CNRS, Reunion University), Reunion Island, France 2BRL Ingénierie, Nimes, France 3Direction InterRégionale de Météo-France pour l’Océan Indien, Reunion Island, France 4Bureau de Recherches Géologiques et Minières, Orléans, France

Session 4.2 – February 8, 2018, 1530-1545

In this study high-resolution (2 km) ensemble simulations of tropical cyclone are performed over the southwest Indian Ocean using the non-hydrostatic model MESO-NH. In contrast to conventional ensemble simulations, in which the initial state of each member is generally perturbed, all members are initialized from the same mesoscale 3D-VAR analysis. Each member is nevertheless forced by a different member of the ECMWF’s Ensemble Prediction System (EPS), which allows for the production of 51 distinct high resolution forecasts of the same event from the same initial conditions. This ensemble forecast of rainfall is then used to force an hydrological model and to assess the sensitivity of hydrological forecasts to uncertainties in rainfall prediction (intensity, amount, location).

The objective of this study is twofold: i) objectively assess the impact of lateral boundary conditions on tropical cyclone prediction, and ii) evaluate the benefit of using high-resolution ensemble rainfall forecast for river hydraulics and inland flood forecast under cyclonic conditions. In order to illustrate this study, probabilistic rainfall and hydrological forecasts produced during the passage of Intense Tropical Cyclone Bejisa (30 December 2013–3 January 2014) over the mountainous tropical island of La Reunion will be presented. A particular emphasis will be put on the way to integrate these new information in crisis management organization.

282

A parametric model for hailstorm development at southeast Australia Cheung, Kevin1, Magill, Christina1, Rasuly, Ali Akbar1

Presenting author’s e-mail: [email protected]

1Macquarie University, NSW, Australia

Session 4.2 – February 8, 2018, 1645-1700

Severe thunderstorm and hailstorm are among the costliest meteorological hazards in Australia, especially over its eastern coastal regions of Queensland and New South Wales. How storm activity would change under anthropogenic warming is a urgent question to answer. Related studies have mostly been conducted in North America (Changnon and Changnon 2000; Trapp et al. 2007, 2009; Brooks 2013; Diffenbaugh et al. 2013; Seeley and Romps 2015) and only a few in Australia (e.g., Niall and Walsh 2005; Allen et al. 2014). Most of these studies examined the convective available potential energy (CAPE) and low-level vertical wind shear (VWS) as the key environmental factors that determine storm activity. Increased water vapour in the boundary layer was also found to contribute to the projected enhancement in storm environment based on CAPE and VWS estimates in climate models. However, studies on the local hailstorms (McBurney 2012) revealed some unique features in the storm environment. The local severe hailstorms mostly developed under only moderate CAPE, high directional shear or helicity, and often accompanied with midlevel dry slot. This study aims to develop a parametric model for hailstorm development for Australia, which will be applicable to estimate the future behaviour of storm number and severity based on climate projection. Besides CAPE and deep and shallow VWS, more than twenty other environmental parameters have been analysed for the historical storms from the 1950s. Various representations of the lifted index and the wet bulb zero height, together with CAPE and deep VWS, are identified as critical factors that determine local hailstorm development.

283

Multi-week tropical cyclone prediction in ACCESS-S1 and the role of the MJO Camp, Joanne1, Wheeler, Matthew2, Hendon, Harry2, Gregory, Paul2, Marshall, Andrew2, Tory, Kevin2, Watkins, Andrew2, MacLachlan, Craig1, Kuleshov, Yuriy2

Presenting author’s e-mail: [email protected]

1Met Office Hadley Centre, Exeter, UK 2Bureau of Meteorology, Victoria, Australia

Session 4.2 – February 8, 2018, 1700-1715

The Australian Bureau of Meteorology (BoM) seasonal forecasting system (ACCESS-S1), based on the UK Met Office seasonal forecasting system (GloSea5), is investigated for the prediction of the weekly occurrence of tropical cyclone (TC) activity in the Southern Hemisphere. On multi-week timescales the Madden-Julian Oscillation (MJO) has previously been shown to be a major driver of TC predictability. ACCESS-S1 shows high skill for predictions of the MJO out to a lead time of ~30 days, and is able to reproduce the observed modulation of TC activity by the MJO in the Southern Hemisphere. In particular, ACCESS-S1 shows a clear eastward propagation of enhanced TC activity with the enhanced convective phase of the MJO, as well as reduced TC activity both before and after the enhanced MJO phase. MJO modulated changes in the large-scale environmental parameters associated with TC genesis, such as 850 hPa absolute vorticity, 600 hPa relative humidity and 850–200 hPa vertical wind shear, are well captured by ACCESS-S1 except off the northwest coast of Australia. There, the change in the large-scale environment and associated TC activity is too weak in the model. Probabilistic forecast verification shows that ACCESS-S1 is able to provide skillful forecasts of TC occurrence out to the end of week 5 if forecasts are calibrated to take into account model biases in TC frequency. Two different calibration strategies are tested: the first is a simple constant scaling factor applied everywhere and for all forecast leads; the second applies a different scaling factor for different regions and lead times. Results of this study suggest that ACCESS-S1 can provide skillful multi-week forecasts of TC occurrence for the Southern Hemisphere, greatly enhancing the current TC forecast availability.

284

Objective reanalysis of Tropical Cyclone wind radii parameters using the Deviation Angle Variance Technique Stark, Clair1, Ritchie, Elizabeth A.1, Tyo, J. Scott1, Burton, Andrew2, Courtney, Joe2

Presenting author’s e-mail: [email protected]

1University of New South Wales - Canberra, ACT, Australia 2Bureau of Meteorology, Perth WA

Session 4.2 – February 8, 2018, 1715-1730

Winds produced by tropical cyclones (TCs) are destructive and widespread. Timely predictions of TC wind fields are necessary to predict and manage the impact of cyclones while long-term historical analyses are important for forecasting climate trends. Forecasters are particularly interested in the wind radii parameter – a measure of the maximum radial extent of the 34, 48 and 64 knot winds. Historically, estimation of these wind field parameters have been limited by sparse, non-uniform (spatial and temporal) observations, and, until recently, were a low priority. A variety of analysis techniques have been developed to improve these estimations using in-situ (e.g., aircraft or buoys) and/or remotely sensed data, however these techniques either have low resolution (e.g., ~48 km) or low or irregular sampling intervals and are therefore not ideal for real time predictions.

A methodology, with higher sampling frequency and lower mean absolute errors, has been developed to determine wind radii parameters using the deviation angle variance technique (DAV-T). DAV-T measures the axisymmetry of cloud structures relative to a reference point in IR satellite images to determine the level of cloud organisation in tropical systems. DAV-T has been used to track cloud clusters, determine tropical cyclogenesis, and estimate tropical cyclone intensity. More recently, DAV- T maps (for analysing TC cyclogenesis) have been used, along with best-track data from the Cooperative Institute for Research in the Atmosphere (CIRA) and model data from the Statistical Hurricane Intensity Prediction Scheme (SHIPS), to create multiple linear regression models of half hourly TC wind radii values in the North Atlantic. This method will be used in an objective reanalysis to create an improved historical record of TC wind radii parameters in the Australian region for the geostationary satellite era (~1981 – present day). In this presentation, we will discuss the data, methodology, and results.

285

High-impact severe thunderstorm events in southeast Queensland Turner, Kathryn1, Soderholm, Joshua1, Wedd, Tony2, Callaghan, Jeffrey2, Grant, David2, Richter, Harald2

Presenting authors email: [email protected]

1The University of Queensland, QLD, Australia 2Australian Bureau of Meteorology, Australia

Session 4.2 – February 8, 2018, 1730-1745

The southeast Queensland (SEQ) region has among the highest population density in Australia. Typically the region experiences a high volume of thunderstorm events through the September to February storm season. Since 1985, four destructive thunderstorm events with similar characteristics have affected the Brisbane metropolitan area and produced damage bills of $2.26 billion (18th January 1985), $24 million (24th December 1989), $422 million (16th November 2008) and AU$1.3 billion (27th November 2014) in 2016 Australian dollars. The events produced a variety of high impact weather, including large hailstones, destructive winds, and multiple tornadoes. All four events occurred in conjunction with a south-easterly wind change on the Queensland/New South Wales border around midday which moved through the populated SEQ region during the afternoon at the time of maximum heating.

This paper presents an analysis for distinguishing these events from typical storm days in SEQ. The results identify key differences between a “typical” storm day and environments during these four high-impact severe storms. These key environmental differences provide the basis for more timely and accurate forecasting which may be used operationally by forecasters for future seasons. The four events were compared and contrasted using upper air soundings, weather station observations, radar, and upper-level reanalysis. Further to this, a climatology of all south-easterly changes that occurred in SEQ during September to February 2007 to 2016 storm seasons was completed to identify the characteristics that separate these events from lower impact storms or null case days. Ingredients such as deep layers of low level moisture, a moderate cap, and low wind speeds below 500 hPa when combined with the cool south-easterly wind change can be the key to developing a high-impact thunderstorm.

286

4.3 Special session on renewable energy – the effects of weather and climate on integrating renewables into our energy industry Mathematical and statistical tools for energy meteorology Boland, John1

Presenting author’s e-mail: [email protected]

1University of South Australia, SA, Australia

Session 4.3 – February 6, 2018, 1100-1115

I will discuss two tools that I and colleagues have developed to aid energy analysis:

1. The Boland-Ridley-Lauret (BRL) diffuse radiation model The Australian National Home Energy Ratings Scheme (NatHERS) is used to assign star ratings to a house design, and currently a rating of six stars out of ten is needed for approval. For evaluating the star rating, knowledge of the three components of solar radiation are needed. They are global radiation on a horizontal surface (GHI) and its contributing factors of direct and diffuse. In a similar manner, to optimise the location of a solar farm, one also needs knowledge of all three. Often only global is available, either measured or inferred from satellite images. The BRL model has wide usage in splitting global into the two components. I will describe a recent use of BRL in Brazil. http://www.sciencedirect.com/science/article/pii/S0960148117301635

2. Short term probabilistic solar forecasting tool. This is in the time scale of a few minutes to 1- 2 hours. - http://www.sciencedirect.com/science/article/pii/S0038092X16300342

287

Evaluation and improvement of solar irradiance forecasting skills of the Australian Bureau of Meteorology’s ACCESS models Joshi, Bibek1, Sproul, Alistair Bruce1, Copper, Jessie Kai1, Kay, Merlinde1

Presenting author’s e-mail: [email protected]

1School of Photovoltaics and Renewable Energy Engineering, University of New South Wales, NSW, Australia

Session 4.3 – February 6, 2018, 1115-1130

The rapidly increasing penetration of solar power into the electricity grid has created the need for accurate solar power forecasts for facilitating safe and reliable electricity grid management. Numerical Weather Predictions (NWP) is currently the best tool for forecasting solar irradiance beyond several hours ahead, which is crucial particularly for applications in day-ahead energy markets as well as for energy management at different scales, ranging from utility-wide to residential level. In this study, we evaluated the ability of the Australian Bureau of Meteorology’s (BOM) numerical weather prediction system, the Australian Community Climate and Earth-System Simulator (ACCESS) model, to forecast solar irradiance. The day-ahead forecasts of global horizontal irradiance from the regional (ACCESS-R APS1) and the city scale (ACCESS-C APS1 and ACCESS-C APS2) mesoscale models were validated against irradiance measurements from eight ground stations over Australia. Further, we developed a neural network based post-processing routine using irradiance forecasts from the surrounding grid points. While all the models generally under-predicted irradiance, the higher resolution ACCESS-C models outperformed the lower resolution ACCESS-R both in terms of Root Mean Square Error (RMSE) and Kolmogorov-Smirnov Integral (KSI) at most of the sites. Moreover, the highest resolution ACCESS- C APS2 model best predicted the forecast distribution. The developed post-processing routine demonstrates potential for improving forecast performance.

288

Assessment of solar irradiance predictions using WRF on days of high intermittency Prasad, Abhnil1, Kay, Merlinde2

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, University of New South Wales, NSW, Australia 2School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, NSW, Australia

Session 4.3 – February 6, 2018, 1130-1145

Solar irradiance reaching the surface is often obscured by clouds that significantly reduce the production of solar power. Often, improvements in the short-term predictability of clouds and irradiance in numerical weather prediction models can assist grid operators in managing intermittent solar generated electricity. In this study, the performance of the Weather Research and Forecasting (WRF) model in forecasting different components of solar irradiance including Global Horizontal irradiance (GHI) and Direct Normal Irradiance (DNI) will be reported under days of high intermittency at Mildura site located on the border of New South Wales and Victoria, Australia. Initially, four case days were chosen with highly intermittent solar irradiance observed at Mildura site while another four days of low intermittency were taken as control for clear days. A specific configuration and augmentation of WRF model (v 3.6.1) designed for solar energy applications (WRF-SOLAR) with optimum physics ensemble derived from literature over Australia was used to simulate solar irradiance with four nested domains nudged to ERA-Interim boundary conditions at grid resolutions (45km, 15km, 5 km, 1.7km) centred over Mildura. The Bureau of Meteorology (BOM) station dataset available at minute timescales and hourly derived satellite irradiance products were used to validate the simulated products. Also, surface variables including winds, air temperature and humidity were initially compared to ensure observed meteorology is preserved in simulations of all case days. Results from all the clear and cloudy case days simulated at different resolutions and sites will also be discussed.

289

Wind resource assessment for Tahiti, French Polynesia Hopuare, Marania1, Lucas-Svay, Lorene1, Ortega, Pascal1

Presenting author’s e-mail: [email protected]

1GePaSud Laboratory, University of French Polynesia, Tahiti, French Polynesia

Session 4.3 – February 6, 2018, 1145-1200

This study presents the work conducted to quantitively assess the wind energy potential of Tahiti, French Polynesia.

A statistical-dynamical downscaling procedure is used to investigate regional meteorological fields with 1.33 km resolution. Geostrophic wind components are considered the main parameters that characterize large-scale weather situations. Daily wind fields at 500 hPa from 30 years of ERA Interim reanalysis data undergo a cluster analysis (k-means). 55 clusters, each considered a representative weather situation, are identified, as well as their relative frequency of occurrence. These clusters are used as initial and boundary conditions for highly-resolved simulations, using the mesoscale model WRF-ARW.

The resulting wind fields are then weighted together using the frequencies of the corresponding large- scale weather classes to build a fictive year. Results are compared with measurements from weather stations in Tahiti. Primary conclusions are drawn concerning the feasibility of wind energy production systems in Tahiti. One particular site has been identified as suitable to host wind power plants and is further examined here. The annual power output is assessed thanks to the wind speed distribution and the wind power curve of a 275 kW wind turbine.

290

Where should new wind energy sites be located to avoid climate and financial risk? Evans, Jason1, Kay, Merlinde2, Prasad, Abhnil1, Pitman, Andy1

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre and ARC Centre of Excellence for Climate Extremes, University of New South Wales, NSW, Australia 2School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, NSW, Australia

Session 4.3 – February 6, 2018, 1200-1215

Resource assessment and planning for new renewable sites, has focused on numerical modelling or long term measurements taken at a site, in effect looking to past behaviour of the resource. For future developments, from a risk management perspective an investor would want to know the reliability of the resource in the future. There is however a large gap at present in linking the effects of how the climate is changing in regard to where we are choosing renewable sites. It is of great importance to determine if the sites we are choosing now will still be both optimal and economically viable in 20 years’ time due to changes in the climate.

In order to assess the future economic viability of wind energy we have run a 12-member ensemble of high-resolution regional climate simulations forced by Coupled Model Intercomparison Project (CMIP) output. We looked at the impact climate change had on wind energy for the recent past, near future and far future. The Levelised Cost of Energy (LCOE) was used as a measure to ascertain the risk with continuing investment in future wind energy. Our results show that the LCOE increases negligibly in the future in regions with significant existing installed capacity. We also find projected small reductions in wind energy, but with technological developments taken into account the LCOE decreases by around 30%. These results confirm the viability for existing wind farms, and enhance the economic viability of proposed wind farms in Western Australian and Tasmania.

291

Bureau of Meteorology data and services for renewable energy industry and research Murphy, Brad1, Jakob, Doerte1, Black, Mitchell1, Grant, Ian1, Rikus, Lawrie1, Walland, David1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 4.3 – February 6, 2018, 1215-1230

The Bureau of Meteorology currently records, processes and makes available a wide range of observations and data of significant benefit to the renewable energy industry and related research community. These include: ground observations of multiple solar radiation parameters every minute from a small number of stations around Australia; hourly global horizontal and direct normal irradiance grids from satellite data at 5 km across Australia; lower spatial and temporal resolution solar data at a much larger number of sites; wind observations from many ground automatic weather stations; wind and surface solar radiation forecasts across Australia; and many others.

Current and planned projects will significantly improve data processing times and delivery mechanisms, and produce several enhanced datasets. Data will be delivered in near-real-time and through applications with expanded and simpler data access and through APIs, to serve data more easily to users and from machine-to-machine. Gridded products will be transitioned to higher spatial (2 km or better) and temporal (10 minutes) resolution; and an exciting new data source from a high- resolution atmospheric reanalysis for Australia.

The reanalysis will be based on the ACCESS weather model, covering Australia and the surrounding regions, providing nearly 100 parameters at hourly time steps at approximately 12-km resolution. The first 6-year time slice (2010 to 2015) is expected to become available in late 2017. For RE applications, perhaps the most groundbreaking datasets will be wind at the surface and up to 80 km into the atmosphere, as well as multiple radiation parameters, cloud, temperature, humidity, rainfall and others. These data will offer major improvements over other similar products as they have been specifically calculated, optimised and validated for the Australian region using a temporally consistent data assimilation system. The reanalysis will ultimately represent a suite of high-resolution gridded climate datasets and as such will prove valuable for a large range of applications.

292

4.5 East coast lows – drivers of variability and associated extremes A physically-based classification of east coast lows Cavicchia, Leone1, Dowdy, Andrew2, Walsh, Kevin1

Presenting author’s e-mail: [email protected]

1University of Melbourne, VIC, Australia 2Bureau of Meteorology, Australia

Session 4.5 – February 9, 2018, 1200-1215

The subtropical east coast region of Australia is characterised by the frequent occurrence of low pressure systems, known as east coast lows. While the term "east coast low" refers to a broad classification of events, it has been argued that different east coast lows can have substantial differences in their nature, being dominated by baroclinic and barotropic processes in different degrees.

The purpose of this work is to establish an approach aimed at a physically-based classification of east coast lows, based on the analysis of phase space parameters and cyclone energetics. In order to do so, we revisit two well-known historical east cost low cases following such approach (the Duck storm of March 2001 and the Pasha Bulker storm of June 2007), and show that they are representative of the two "extremes'' of the east coast low spectrum.

By focussing on the storms full three-dimensional structure and exploiting the cyclone phase space analysis, we show that one storm has features similar to a typical extra-tropical frontal storm, while the other has hybrid characteristics. Furthermore, we examine the limited area energetics of the atmosphere for the east coast lows occurrence times, and show that the two cyclones are associated with different signatures in the energy conversion terms.

We argue that such a classification approach, when applied systematically to automatically detected storms in multi-decadal reanalysis or modelling datasets, has the potential to advance our understanding of the occurrence and intensification of east coast lows and possibly of subtropical cyclones in diverse regions worldwide.

293

East Coast Lows – classification and terminology used by the New South Wales RFC Louis, Simon

Session 4.5 – February 9, 2018, 1215-1230

East Coast Lows (ECLs) are one of the key synoptic drivers of severe weather for eastern New South Wales, and have the potential to cause significant impact on the community. Major East Coast Low events in the last ten years include the Pasha Bulker storm in 2007, the Dungog storm in 2015, and the June 2016 storm that caused extensive coastal damage. Over time emergency services, the media and the broader community have come to associate the term ‘East Coast Low’ with significant weather impacts, and as a result labelling an upcoming system as an ECL can result in a stronger response from these groups. Most climatological studies and methods for classifying ECLs focus more on dynamical meteorological processes and synoptic regimes that can lead to cyclogenesis in the western Tasman, and often do not take impact into account. This misalignment between dynamical definitions what an ECL is and the community association with high impacts can lead to challenges in operationally communicating the appropriate level of risk.

In this presentation I will outline an operationally focussed method for classifying ECLs that has been developed in the New South Wales Regional Forecast Centre, using some brief case studies. This terminology is used in conjunction with the NSW State Emergency Service and media outlets as a communication tool to assist with prompting an appropriate level of response to upcoming weather events.

294

Reassessing "objective" databases of ECLs using satellite data Pepler, Acacia1, Di Luca, Alejandro2, Evans, Jason2

Email: [email protected]

1Bureau of Meteorology, NSW, Australia 2University of New South Wales, NSW, Australia

Session 4.5 – February 9, 2018, 1230-1245

East Coast Lows (ECLs) cause a large proportion of significant weather events on the east coast of Australia. A greater understanding of how East Coast Lows are represented in gridded data sets, including how the spatial resolution affects the degree of confidence in this representation, is important for constraining uncertainties associated with projecting the influence of climate change on these systems and the extreme weather that they can cause. However, there remains considerable uncertainty as to the "true" frequency and distribution of ECLs, which is sensitive to both the method used for identifying cyclones as well as the reanalysis dataset used, particularly at high resolutions. Since cyclones have characteristic wind and rain patterns, here we use the CCMP satellite winds and TRMM satellite rainfall to assess the ability of the ERA-Interim, JRA55, and MERRA reanalyses to reproduce "real" ECLs, and identify the best reanalysis datasets to use for future studies.

295

Wave direction and spatial variability in coastal erosion due to east coast lows: high-resolution observations from the June 2016 event Harley, Mitchell1, Turner, Ian1, Middleton, Jason1, Kinsela, Michael2, Splinter, Kristen1, Hanslow, David2

Presenting author’s e-mail: [email protected]

1UNSW Sydney, NSW, Australia 2Office of Environment and Heritage, NSW, Australia

Session 4.5 – February 9, 2018, 1245-1300

In June 2016 a severe east coast low impacted the coastline of southeast Australia that resulted in substantial damage extending from southern Queensland to Tasmania. With extreme conditions forecast six days in advance of the storm, a rapid response coastal monitoring team was able to capture unique regional-scale pre- and post-storm measurements using Airborne Lidar and other technologies. High-resolution data from over 177 km of sandy coastline reveal that 11.5 million cubic metres of sand was removed from the subaerial beach over the three days of the storm, which is comparable in magnitude to the amount erosion observed during the 2012 Hurricane Sandy event on the east coast of the U.S.A. At Narrabeen-Collaroy Beach (located within the Sydney metropolitan region), where beach transects have been monitored on a monthly basis since 1976, erosion was found to be the largest over the entire 41-year monitoring record.

Despite the severity of the June 2016 east coast low in terms of impacts at the coastline, deepwater wave heights observed during this event were only considered moderate for this regional setting (equivalent only to a 1-in-5 year event) and almost 2 metres lower than a similar event that struck the same coastline in April 2015. The June 2016 event was instead notable for its unusual wave direction, which approached the coast predominately from the east in comparison to the south to south-easterly wave direction of most storm events in this region. Spatial variability in the beach response along the coast was observed to be strongly controlled by exposure to these easterly waves. The results of this study highlight the strong dependence of coastal response to east coast lows on wave directionality and we therefore call for an increased research focus on possible shifts in wave directionality associated with such extreme events.

296

4.6 Impact and risk assessment for weather extremes Towards a consistent global database of tropical cyclone risk Holland, Greg1,2, Done, James M.1,2, Ge, Ming1, Wang, Yuqing3

Presenting author’s e-mail: [email protected]

1Capacity Center for Climate and Weather Extremes, National Center for Atmospheric Research, Boulder CO, US. 2Willis Research Network, London UK. 3International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaii HI, US.

Session 4.6 – February 9, 2018, 0930-0945

An approach to modeling global tropical cyclone wind footprints will be described, first by developing a historical set of wind footprints derived from observed tropical cyclone data, then by extending this to a comprehensive synthetic data base for current climate.

Gradient-level pressure and wind data are derived from the Holland et al. (2010) parametric approach and used to drive a modified version of the Kepert and Wang (2001, KW) 3-dimensional boundary- layer model. Based on the dry primitive equations, and using prognostic turbulence kinetic energy, the modified model spins up a steady state boundary layer wind structure in balance with the applied forcing. The modifications account for terrain effects and changes in surface roughness - and to allow surface wind simulation under a time-evolving hurricane. These are designed to provide a detailed indication of terrain effects while retaining sufficient computational speed to enable simulation of many thousands of synthetic storms within reasonable computing resources. The applied combination of physical reasoning and testing on observed cases will be described, together with direct comparisons with observations and the hybrid Weather Research and Forecasting model described by Bruyere et al (2017).

This approach enables event-set generation in regions of sparse historical data, understanding inland wind risk in regions of complex topography, validate existing catastrophe models in the region, and informing long-term views of tropical cyclone risk. Aspects of these will be illustrated based on a derived global wind footprint dataset and a synthetic tropical cyclone data set for eastern Australia developed by coupling the boundary-layer model with the Tropical Cyclone Risk Model from Geoscience Australia. Use of the data base to directly assess Cyclone Damage Potential (CDP) also will be discussed.

297

A new world of extreme weather King, Philip1, Morgan, Adam1, Williams, Scott1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 4.6 – February 9, 2018, 0945-1000

From across society, there is an increasing demand for The Bureau of Meteorology to offer enhanced information and products in relation to extreme weather. This is tracking the rising trend in frequency and impact of severe weather events. In response to this demand, the Extreme Weather Desk (EWD) is making National Hazard Impact and Risk Assessment an integral part of its operations. By adopting a classification system for describing the impact and risk of weather hazards on the community and on the Bureau’s real-time operations, the Bureau is responding to this demand in multiple ways. This talk will explain how the Bureau is:

• developing graphical products and a systematic approach to communicating impact, probability-based weather intelligence internally and to our emergency service partners, • incorporating hazard impact and probability intelligence into our contingency and resource planning, so we can better “surge” during high or extreme weather events, • utilising hazard impact data within the same classification system for post event review and analysis, ensuring that lessons and recommendations after high impact events flow directly through to service improvements.

298

The Melbourne thunderstorm asthma epidemic of 21 November 2016 Bannister, Tony1, Williams, Ted1, Csutoros, Danny2, Looker, Clare2

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia 2Department of Health and Human Services, VIC, Australia

Session 4.6 – February 9, 2018, 1000-1015

On the evening of Monday 21 November 2016, the first very hot day across the state since March 2016, Victoria, Australia, experienced severe thunderstorm activity. These storms moved from the west of the state, through Geelong and across the Melbourne area. The storms, themselves not remarkable, were followed by an epidemic thunderstorm asthma event, the likes of which in terms of size, severity and acuity had never before been seen, nor even imagined, let alone planned for. It resulted in thousands of people developing breathing difficulties in a very short period of time, creating extraordinary and unparalleled demand across the health service system. For many of those affected this was their first asthma attack. From 6 pm, Ambulance Victoria, hospital emergency departments, primary care providers, pharmacies and ancillary health services felt the shock of this unprecedented surge in patients with asthma symptoms and respiratory distress. The large numbers of people seeking emergency medical assistance continued throughout the night and into the next day, with hospital admissions peaking on 22 November but remaining elevated throughout the remainder of that month. The State Corner is investigating nine tragic deaths thought to be associated with this epidemic thunderstorm asthma event. The event was unprecedented internationally.

We will describe the 21 November 2016 thunderstorm asthma event in Melbourne, including the environmental and atmospheric conditions leading up to the event. We will also present the impacts on Ambulance Victoria’s demand, emergency department presentations and hospital and intensive care unit admissions. Finally details of the trial 2017-18 Victorian Epidemic Thunderstorm Asthma Risk forecast service will be discussed.

299

Exploring unseen disaster scenarios: interrogating stochastic tropical cyclone event catalogues for hazard and impact assessment Arthur, Craig1, Krause, Claire1, Sanabria, Augusto1

Presenting author’s e-mail: [email protected]

1Geoscience Australia, ACT, Australia

Session 4.6 – February 9, 2018, 1015-1030

Geoscience Australia has previously developed a stochastic model of tropical cyclones (TCs) for hazard assessment – the Tropical Cyclone Risk Model (TCRM). TCRM was designed to address the challenges of inferring average recurrence interval wind speeds for application to building design standards. In TCRM, there were identified shortcomings in the format of the data produced. The catalogue grouped events into annual collections, making it difficult for users to extract individual events for more detailed modelling, or applications outside of building design criteria.

Based on user feedback and our own experiences, TCRM has undergone significant revision to ensure the data produced by the model are readily accessible and deliver the information required by end- users. Outputs are in machine-readable formats, and delivered via a range of protocols. TC tracks are stored in annual collections, using compressed netCDF files to minimise storage. The wind fields for each individual TC event are stored in CF-compliant netCDF files and can be individually inspected.

A relational database containing details of the event catalogue enables users to interrogate the catalogue in a meaningful way – for example to select all events that pass within a specified distance of a location, or all events that exceed some threshold such as a specific average recurrence interval, or TC intensity category. This way, users can select an event for their specific purpose without having to manually search the entire catalogue, opening up the possibilities for applications using stochastic TC scenarios. With the database, users can extract TC events that may have never before been observed – such as a direct strike of a category 5 cyclone on Cairns. Emergency managers can use scenarios like this to develop or test contingency plans using realistic, but previously unseen events.

Some example TC scenarios will be presented, along with details of improvements to underlying model algorithms.

300

A global investigation of the impacts of landfalling tropical cyclones on societies Ritchie, Elizabeth A.1, Wood, Kim M.2, Balukas, Denise3

Presenting author’s e-mail: [email protected]

1University of New South Wales - Canberra, ACT, Australia 2Mississippi State University, MS USA 3Cooperative Institute for Mesoscale Meteorological Studies, OK USA

Session 4.6 – February 9, 2018, 1030-1045

Landfalling tropical cyclones (TCs) result in much devastation and numerous fatalities around the world each and every year. The impacts of TC landfall to specific communities and societal groups vary widely. These variations in impacts are due not only to the strength and intensity of the TC at landfall, but also to a given society’s vulnerability and resiliency to these stresses at the time of the TC event. Societies have various levels of vulnerability to TC landfall based on many factors including education, preparedness, personal history with previous events, and governmental infrastructure. The frequency of landfalling events is an important factor for population and ecological vulnerability, not only due to the immediate impacts associated with landfall events, but also for the long-term socioeconomic development of the region.

This research seeks to gain insight into the many factors that determine the impact of landfalling TCs. An analysis of the physical characteristics of the spatial and temporal patterns of landfalling events, the socioeconomic and demographic conditions of the location at the time of landfall, and the range of impacts resulting from all landfalling TCs from 1998 to 2013 is presented on scales ranging from global to regional. A comparison of the levels of impacts, which result from TC landfall in developing verses developed countries, is performed. Using both socio-economic and geographic data from sources including, but not limited to the Emergency Events Database, World Bank, the Socioeconomic Data and Applications Center, and the International Best track Archive for Climate Stewardship we will attempt to quantify the level of vulnerability and resiliency of each impacted region by assessing the spatial and temporal trends in TC impacts. The use of socio-economic data in concert with physical storm parameters will allow for a more robust understanding of the ramifications of landfalling TCs.

301

Tropical cyclone Debbie: investigation of building performace (wind loads, wind driven rain and storm surge) Henderson, David1, Smith, Daniel1, Boughton, Geoff1, Falck, Debbie1, Ginger, John1, Parackal, Korah1, Humphreys, Mitch1, Bodhinayake, Geeth1, Mason, Matthew2, Kloetzke, Thomas2, Krupar III, Richard3

Presenting author’s e-mail: [email protected]

1Cyclone Testing Station, James Cook University, Qld, Australia 2University of Queensland, Qld, Australia 3Center for Disaster Resilience, University of Maryland, MD, USA

Session 4.6 – February 9, 2018, 1045-1100

Tropical Cyclone Debbie made landfall on the Whitsundays in North Queensland on 28 March 2017. Field surveys were conducted to investigate the performance of buildings (housing, larger residential structures such as apartments, strata properties and resort accommodation; public buildings and sheds) impacted by TC Debbie. The study area included the communities of Bowen, Proserpine, Airlie Beach, Hamilton Island, Shute Harbour, Hydeaway Bay, Dingo Beach, Wilson Beach and Conway Beach.

The field studies:

• Used the SWIRLnet and BoM data to estimate the peak gust experienced at a number of different locations in the affected area. • Examined contemporary buildings constructed using the current regulations to determine whether their performance was appropriate for the estimated wind speeds they experienced. Where damage was greater than that expected, common failures were documented in sufficient detail to allow recommendations for changes to regulations or construction methods as appropriate. • Examined patterns of damage to determine whether there are any types of structures or structural elements that appear to have systematic weaknesses. • Assessed the capacity of buildings to withstand wind loading and debris impact loading. • Assessed the extent of damage to houses and larger buildings from wind-driven rain, focusing on the performance of windows, doors, gutters and flashings. • Examined older houses and other buildings to determine the need for retrofitting, and assessed the effectiveness of any structural upgrades. • Determined the extent of structural damage from storm surge in the study area.

Recommendations include: Improving detailing for roof to wall connections for buildings in exposed locations (topographic wind speed up); improved fixing of flashings, retrofitting options for older buildings; and revision of storm surge guidelines. Work is continuing to assess aspects of the long duration of TC Debbie in terms of load cycles on building components.

The report on building performance is available at… https://www.jcu.edu.au/__data/assets/pdf_file/0009/461178/TC-Debbie-report.pdf

302

Quantitative modelling of vulnerability to severe wind Wehner, Martin1, Ryu, Hyeuk1, Ginger, John2, Edwards, Mark1, Henderson, David2, Parackal, Korah2, Smith, Daniel2

Presenting author’s e-mail: [email protected]

1Geoscience Australia, ACT, Australia 2Cyclone Testing Station, College of Science and Engineering, James Cook University, QLD, Australia

Session 4.6 – February 9, 2018, 1130-1145

Modelling of the risk posed by the impacts of extreme weather events requires knowledge of the vulnerability, or performance, of building assets. Furthermore, to assess the benefits of mitigation an ability to quantitatively model the change in vulnerability associated with mitigation actions is required. In Australia past efforts at establishing vulnerability relationships between building damage and severe wind have centred on empirical techniques, using data from damage surveys or insurance losses, and heuristic techniques. Neither of these methods permits the change in vulnerability afforded by mitigation work to be quantitatively modelled.

The Bushfire and Natural Hazards CRC project “Improving the Resilience of Existing Housing to Severe Wind Events” is developing a software tool, Vulnerability and Adaption to Wind Simulation (VAWS), to provide a quantitative vulnerability model for Australian house types. It is based on the premise that overall building damage is strongly related to the failure of key connections. The software uses a Monte Carlo approach whereby numerous realisations of a single generic house type are subjected to an increasing gust wind speed and the loss at each wind speed is calculated. Each realisation of the house varies from others as many key building parameters, such as connection strength, are sampled from probability distributions.

For each instance, at each wind speed, the number and type of failed connections are related to damage states and extents of damage which permits the repair cost to be calculated. The repair cost is adjusted for the repair of debris impact damage and water ingress damage. The modelling of mitigation is easily accomplished by rerunning a house modelled with the probability distribution of an upgraded connection’s strength substituted.

The software tool provides quantitative measures of reduced vulnerability that can be used in assessing the incremental effectiveness of a range of mitigation strategies in economic terms.

303

Impact-based forecasting in the coastal zone: East Coast Lows Richter, Harald1, Arthur, Craig2, Wehner, Martin2, Krause, Claire2, Ebert, Beth1, Kepert, Jeff1, Stringer, Russell1, Dunford, Mark2, Sexton, Jane2, Edwards, Mark2

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Victoria, Australia 2Geoscience Australia, ACT, Australia

Session 4.6 – February 9, 2018, 1145-1200

East coast lows (ECL) are a regular high-impact hydro-meteorological event in Australia, primarily affecting the eastern seaboard from southern Queensland to eastern Victoria. These storms affect the most densely populated regions of Australia, with the potential to cause damaging impacts from gale- or storm-force winds, widespread rain and flooding and very rough seas and prolonged heavy swells in coastal waters. With the substantial improvements in weather forecast accuracy and resolution over recent decades, and advances in assessment of asset exposure and vulnerability at the national scale, there now exists the potential to provide emergency managers, owners and operators of critical infrastructure and other stakeholders in the disaster planning and response arena with impact-based forecasts and warning information.

In this presentation, we will provide the context to a new Bushfire and Natural Hazards CRC project: Impact-based forecasting for the coastal zone: East-Coast Lows. The project, a collaborative effort between the Bureau of Meteorology and Geoscience Australia, builds on feedback from emergency management and other stakeholders indicating high demand forecasting of potential impacts. The project also supports the WMO initiative aiming to embed impact-based warning capabilities into operational forecasting for national hydrological and meteorological services.

The project is focusing on the wind and rainfall impacts from the 20-22 April 2015 ECL event over the Hunter region of NSW. The wind and rainfall (hazard) data are provided by a 24-member ensemble of the ACCESS model on a 1.3 km grid. The project is relying on strong engagement from end-users, who will help prioritise assets and impact definitions to support their operational objectives. These same end-users will also be a valuable source of observed damage information caused by extreme weather events, which will be used to develop relationships between forecast hazard levels and likely damage.

304

4.7 Weather – general The continued development of the Bureau of Meteorology’s Numerical Weather Prediction Systems Steinle, Peter1, Sun, Xudong1, Franklin, Charmaine1, Rennie, Susan1, Cooper, Shaun1, Xiao, Yi1, Lee, Jin1, Naughton, Michael1, Lu, Wenming1, Fernon, Joan1, Rikus, Lawrence1, Coleman, Thomas1, Zhu, Hongyan1, Dharssi, Imtiaz1, Ma, Yimin1, Li, Zhihong1, Sulaiman, Asri1, Krysta, Monika1, Fraser, James1, Glowacki, Tomasz1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, VIC, Australia

Session 4.7 – February 5, 2018, 1645-1700

Numerical Weather Prediction (NWP) has been the dominant influence on the improvement in forecast accuracy at weather centres around the world. These gains are due to advances in modelling, observations, data assimilation and high performance computer power. All of these are currently combining to enable the Australian Bureau of Meteorology to undertake a major upgrade of its suite of Numerical Weather Prediction (NWP) systems.

This presentation will discuss the latest systems, and look ahead to the near future. One of the main changes is the introduction of ensemble systems – not just for prediction but also within the assimilation systems. The combination of 4d variational assimilation and ensemble information allows the data assimilation system to better capture the flow dependence of the forecast errors. Another major change is the introduction of convective scale predictions systems – that is modelling systems where deep convection can be explicitly represented using cloud dynamics rather than a convective parametrization. Of course these systems offer much more than just better convection modelling, as the modelling of any phenomena with significant surface forcing will also be greatly improved.

While these systems provide major shifts in forecast accuracy, there are still many areas that are open for further research and development – and the challenge for the future is how these are addressed by the wider Australian meteorological community.

305

Forecasting rainfall over the Mount Lofty Ranges, challenges and downscaling methods Fischer, Jonathan1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, SA, Australia

Session 4.7 – February 5, 2018, 1700-1715

The sharp topographic gradient between the Adelaide Plains and the Mount Lofty Ranges leads to a complex orographically enhanced rainfall pattern over a relatively short distance. Depending on the synoptic type and atmospheric conditions, significant variations in rainfall amounts can be observed between the Adelaide Plains and the Mount Lofty Ranges.

The current forecast process in the South Australian Regional Forecasting Centre (RFC) involves meteorologists inputting various blends of relatively lower resolution Numerical Weather Prediction (NWP) guidance into a Graphical Forecast Editor (GFE) to produce a high resolution gridded rainfall forecast. The problem with this method is that the convective parameterisation schemes in lower resolution NWP models trigger the orographic rainfall processes when an 'upslope' is detected and fail to adequately advect this precipitation over the Ranges. The result is an enhancement which is often of too small a magnitude and misplaced upstream of where it occurs in reality.

To address this problem, the South Australian RFC has built a climatological dataset of the relative rainfall enhancement between Adelaide and the Mt Lofty Ranges under various mesoscale wind, moisture and stability regimes. This dataset is now used in the forecast process in conjunction with climatological reference grids and other existing approaches to improve the overall magnitude and spatial distribution of orographic rainfall enhancement.

306

A high-level framework for assessing the relative performance of two forecast sources Griffiths, Deryn1, Jack, Harry1, Foley, Michael3, Ioanna, Ioannou3, Maoyuan, Liu3, Price, Benjamin2, Loveday, Nicholas2, Taggart, Robert1

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, New South Wales, Australia 2Bureau of Meteorology, Northern Territory, Australia 3Bureau of Meteorology, Victoria, Australia

Session 4.7 – February 5, 2018, 1715-1730

This study presents a framework for the assessment of the relative numerical skill of forecasting systems. The framework is targeted at high-level decision makers who need to weigh the skill of forecasting systems against the resources needed to maintain them. Such assessments are useful for comparing automated forecast processes, and also for quantifying the skill added by forecasters over the automated guidance available to them, allowing for more efficient allocation of forecaster effort.

A summary metric is selected for either a forecast of a quantity or a probability forecast of an event. The difference in this metric between forecast sources is reported in terms of days of skill gained or lost under adoption of one source over the other. Spatial and temporal stratifications are applied in order to identify variations in skill across regions and seasons. The summary metrics provide decision makers with information on where and when one forecast source is likely to outperform the other (in terms of that metric). Forecasters and guidance developers may also wish to know why this variability occurs - this is facilitated through several detailed secondary metrics.

We demonstrate the framework by comparing the Bureau's manually produced 'Chance of Rain' forecast with automated guidance available to forecasters. The methods reveal statistically significant differences in performance across regions and seasons, with both sources exhibiting relative strengths and weaknesses. Such differences are inevitably subject to change under improvements to model performance and forecast policy.

Limitations of this framework include use of only a single forecast type (e.g. numerical, as opposed to text) and summary metric. It is acknowledged, therefore, that there may be certain aspects of forecast performance that the framework fails to address. Following from this study, an analogous assessment of the Bureau's temperature and wind forecast products is being conducted.

307

Theme 5: Land surface processes 5.1 Urban climate How "hot" is too hot? Evaluating acceptable ranges of outdoor thermal comfort in an equatorial urban park Chow, Winston T.L.1, Heng, Su Li1

Presenting author’s e-mail: [email protected]

1Department of Geography, National University of Singapore, Singapore

Session 5.1 – February 7, 2018, 0930-0945

A commonly used heat island mitigation approach is via increasing densities of green-spaces relative to extant urban land cover, which reduces temperatures through a combination of increased shading and evapotranspiration processes. The influence of these green spaces also extends to other urban climate variables e.g. humidity and wind speeds, which are critical factors in outdoor thermal comfort. How urban vegetation affects outdoor thermal comfort – especially in low-latitude cities – is still a relatively new area of inquiry, especially in examining the relationships between measured and perceived thermal comfort. As such, in this study conducted within the Singapore Botanic Gardens, we examined the range of physiological equivalent temperatures (PET) - a widely used thermal comfort index - in which thermal neutrality is attained over spatial (i.e. different parts of the urban park with diversity of plant composition and configuration) and temporal variations (i.e. different monsoon seasons - the dry Southwest monsoon and wet Northeast monsoon). Microclimate observations of air temperature, humidity, wind speeds and globe temperatures over different park sections were measured over eight days, and field surveys (n=1573) of thermal sensation and preference were concurrently taken. From these data, we regressed subjective thermal sensation data on PET to ascertain both neutral and acceptable ranges of this index within the park. Significant differences in the relationship between PET and thermal sensation, preference and comfort were noted between acclimatised and non-acclimatised park users. Lastly we also suggest how these derived PET ranges can be calibrated to account for the equatorial climate in which the park was sited within.

308

Mitigation of Urban Heat Island in the city of Melbourne: Green and Cool Roofs Strategies Hosen, Imran1, Kala, Jatin2, Ng, A.W.M.1, Muthukumaran, S.1

Presenting author’s e-mail: [email protected]

1College of Engineering and Science, Victoria University, Melbourne, Australia 2Environmental and Conservation Sciences, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia

Session 5.1 – February 7, 2018, 0945-1000

Temperatures in cities are often higher than the surrounding non-urban and rural areas. This phenomenon is commonly referred to as the Urban Heat Island (UHI). These effects are induced due to the human modifications of urban surface properties by using different construction materials that reduce vegetated/pervious areas, emit anthropogenic heat and increase surface roughness. This study examines the effectiveness of green and cool roofs in mitigating the UHI in the city of Melbourne in southeast Australia. This study uses the Weather Research and Forecasting (WRFv3.8.1) model coupled with the Urban Canopy Model (UCM) with rooftop parametrizations schemes for conventional, green and cool roofs. The study also examines the impacts of green and cool roofs on the boundary layer structure and effects on the Human Thermal Comfort (HTC) index. Results show that green and cool roofs are very effective strategies in mitigating UHI effects in urban areas. It is noteworthy that the reductions of roof surface UHI effects (surface temperature difference between urban and rural areas) are considerably higher than the near-surface (temperature difference at 2 m between urban and rural areas) UHI effects. The UHI reductions indicate a linear relationship with the increasing green roof fractions, but a slightly non-linear relationship with the increasing albedo of cool roofs. Green roofs and cool roofs also play a significant role in reducing vertical mixing and planetary boundary layer height, and weakening convective rolls. Finally, the additional benefits of green and cool roofs in improving HTC are also analysed. The study demonstrates that the HTC is improved by using green and cool roofs in urban areas, whereas the Universal Thermal Comfort Index (UTCI) is decreased from extreme (UTCI>46 °C) to very strong (UTCI>38 °C) in the city of Melbourne.

309

A mixed physical/statistical city-scale energy demand model for Australia Lipson, Mathew1, Thatcher, Marcus2, Hart, Melissa1

Presenting author’s e-mail: [email protected]

1UNSW Australia, NSW, Australia 2CSIRO, Victoria, Australia

Session 5.1 – February 7, 2018, 1000-1015

The urban environment and the energy use of buildings dynamically interact – for example waste heat from air conditioning and other internal power use is pumped outside, measurably increasing external air temperature and in turn affecting heating and cooling demand inside. Here we present new developments of the Australian Town Energy Budget (aTEB) model, originally developed to simulate land/atmosphere energy fluxes for regional climate modelling. We extend the model to simulate the environment within buildings – including how conduction, radiation, convection, infiltration, occupation and various materials affect the internal air temperature. The extension allows us to efficiently simulate average heating and cooling energy demand at half-hourly to decadal timescales.

Prediction of average energy demand at sub-daily timescales is improved by combining the physics based model with a statistical model developed to estimate half-hourly demand of the Australian National Electricity Market (NEM). The statistical additions modulate heating, cooling and general electricity use estimation over the diurnal cycle, whereas at longer than daily timescales, energy demand is predicted based solely on physical principles.

The model is evaluated for Preston, Melbourne and Toulouse, France. Aggregate electricity and gas observations at half-hourly intervals are scaled to evaluate local energy demand, and flux tower observations are used to evaluate bulk energy exchange. Model predictions are able to match sub- daily, daily and seasonal energy demand observations within the neighbourhood. In addition, simulation of bulk sensible heat flux is improved as anthropogenic inputs are accounted from electricity use, gas and traffic sources.

310

Validation of high resolution Met Office Unified Model over Singapore and analysis of its impacts on local and regional climate Simón-Moral, Andrés1, Dipankar, Anurag2, Roth, Matthias1, Sanchez, Claudio3, Huang, Hans2

Presenting author’s e-mail: [email protected]

1Department of Geography, National University of Singapore, Singapore 2Center for Climate Research Singapore, Singapore 3Met Office, Exeter, UK

Session 5.1 – February 7, 2018, 1015-1030

The city of Singapore represents a challenge for mesoscale modelling due to its highly complex urban morphology. From the mesoscale point of view, the problem is approached by simplifying the morphology which, in the case of Singapore, can lead to a misrepresentation of meteorological fields. Considering its size and morphological characteristics, an impact on the local and regional wind, temperature and precipitation patterns is expected and, hence, its accurate representation within meteorological models is desired. In addition, the constantly developing nature of this city can result in an enhancement of extreme rainfall events.

The present study shows a validation of a version of the Met Office Unified Model (MetUM) over the city of Singapore, where the default science configuration is modified and the MORUSES (Met Office Reading Urban Surface Exchange Scheme) urban canopy parametrization is used to calculate the impact of buildings on the atmosphere. The ability of the modelling system to represent the surface energy fluxes, temperature and humidity is evaluated against observational data from a network of sensors covering different urban fabrics around the city. In addition, the impact of the city state and its surrounding urban areas on the local wind patterns (e.g. land-sea breeze circulations) due to the urban heat island effect and the rugosity is investigated as a first step to analyse the impact on regional precipitation. Results show a good performance in the temperature field, although a systematic overestimation of night cooling is observed.

311

Contribution of surface urban heat island to summer heat waves – a case study of Sydney, Australia Sidiqui, Paras1, Huete, Alfredo1

Presenting author’s e-mail: [email protected]

1University of Technology Sydney, NSW, Australia

Session 5.1 – February 7, 2018, 1030-1045

Urban areas affect the local environment by altering surface albedo, runoff, and the surface energy balance. Such changes give rise to the urban heat island (UHI) effect in the heart of cities urban areas become hotter than nearby rural areas. In context of climate change, elevated urban temperature may modify heat waves in metropolitan areas during summer. In this paper, we analysed the recent heat wave, February 2017, in Sydney, Australia and its impacts on surface urban heat island effect. The objective is to utilise an innovative geostationary, Himawari-8 that provide measurements of the brightness temperature (BT) at 10 minute interval through out the day. The 144 observations per day for Australian region with 10 minute temporal resolution and 2 Km spatial resolution thus enabling monitoring of surface urban heat island (UHI) extracting key diurnal temperature cycle parameters. We found that maximal temperature between urban and rural occurred from 1:00 to 5:00 p.m. During the heat wave, the temperature in urban areas were 5 – 6 oC and 2 – 3 oC higher in rural areas compared to normal days. Analyses of heat wave showed duration of LST was 4 – 5 hours during the day in urban zones whereas in rural zones it’s duration was shorter. For further analysis, the data sets were also compared with MODIS and Landsat data values, which showed a good correlation with Himawari-8 BT data. It is crucial to characterise UHI in urban and its impact on heat wave event to understand our urban environments for better planning of sustainable cities. We conclude that satellite data with high temporal resolution not only provide help in understanding the diurnal cycle of UHI but also mapping heat wave event and its duration.

312

Using urban irrigation and cool roofs to mitigate future heatwaves Jacobs, Stephanie1,2,3, Tapper, Nigel1,3, Gallant, Ailie1,2,3

Presenting author’s e-mail: [email protected]

1Monash University, VIC, Australia 2Australian Research Council Centre of Excellence for Climate System Science 3Co-operative Research Centre for Water Sensitive Cities

Session 5.1 – February 7, 2018, 1045-1100

Heatwaves are the deadliest natural disaster to occur in Australia, with the chances of hotter, longer and more frequent heatwaves in Australia increasing with the warming climate. Urban residents are exposed to higher risks of heat stress during heatwaves because of the urban heat island effect where cities are hotter than their surrounding rural areas. We use the Weather Research and Forecasting model to downscale NCAR Community Earth System Model output to 2km resolution for Melbourne and its surrounding rural areas. Four present climate heatwaves (from 1996-2005) and four future heatwaves (from 2046-2055) using the RCP8.5 scenario are simulated. We measure how effective urban irrigation and cool roofs are at reducing urban temperatures in Melbourne under present and future heatwave conditions. We will investigate how these heat mitigation strategies affect the surface temperature, near surface temperature, wind speed, humidity, net radiation and apparent temperature, a ‘feels like’ index. From this we can assess which regions of Melbourne respond better to the different heat mitigating strategies. We also investigate how future urbanisation affects the intensity of the heatwave, and how resilient urban irrigation and cool roofs are against heatwaves from the future climate.

313

5.3 Land surface processes – general Vegetation responses to extreme wetting and drying events in central Australia using combined satellite and flux tower observations Huete, Alfredo1, Cleverly, James1, Tran, Nguyen Ngoc1, Leng, Song1, Hardtke, Leonardo1, Eamus, Derek1

Presenting author’s e-mail: [email protected]

1University of Technology Sydney, NSW, Australia

Session 5.3 – February 7, 2018, 1130-1145

In 2010-11 a significant wetting event resulted in widespread greening in central Australia, resulting in an exceptionally large land carbon sink anomaly, that impacted the global carbon cycle. Continent- wide rainfall records dating back to 1900 show an intensification of such wet events, particularly over central and northwestern Australia. In early 2017, another intense wet pulse was recorded in semi- arid central Australia, of greater magnitude than 2010-11. Here we analysed a comprehensive array of satellite sensors in combination with eddy-covariance flux measures of GEP from the Alice Springs (mulga) and Ti-Tree (grass) tower sites to characterise the spatial and temporal traces of landscape greening and drying, along with their standard anomalies from MODIS-satellite time series records from year 2000. Sentinel-2 satellite data, at 10m resolution, was used to discriminate spatial patterns of greening and drying, while 10 minute data from the geostationary Himawari-8 satellite was used to trace the daily temporal evolution of the greening and drying cycles. The flux data show vegetation productivity on the same scale as for 2011, and winter NEP exceeding previous winters with elevated GEP exceeding carbon emissions. Satellite data show 2017 as the largest greening event since 2000 (MODIS) with complex spatial patterns of greening and drying attributed to tree-grass extents. Given large scale trends in extreme drying and wetting cycles and associated impacts on vegetation dynamics, Australia's terrestrial ecosystems will be expected to play an increasing role in regional to global scale carbon cycling.

314

Vegetation Disturbance and Recovery: Importance for decadal prediction Haverd, Vanessa1, Thatcher, Marcus1, Canadell, Pep1, Trudinger, Cathy1, Briggs, Peter1, Smith, Ben1

Presenting author’s e-mail: [email protected]

1CSIRO, Australia 2Lund University, Sweden

Session 5.3 – February 7, 2018, 1145-1200

The distribution of natural vegetation, its phenology, and development state are largely controlled by climate, but in turn vegetation systematically affects regional climate via its direct influence on surface roughness, albedo and surface conductance. While predictability of decadal climate variability is widely assumed to be closely associated with external forcing

(eg volcanic activity) and modes of ocean circulation, predictability remains low and other potential sources of predictability, such as vegetation cover and phenology, remain sparsely investigated, especially using high resolution, coupled land-atmosphere modelling approaches.

Here we make use of state-of-the-art parameterisations of vegetation structural dynamics within the CABLE land-surface scheme to assess the impact of dynamic vegetation cover on variability of land- surface properties across south-eastern Australia for 1995-2011, a period that brackets the Millennium Drought. We test our predictions using land-atmosphere exchange data from the TERN- OzFlux Network. Further, we present preliminary results from the CCAM regional climate model dynamically coupled to land surface dynamics of CABLE. In an application of the model over south- eastern Australia under scenarios of fixed and dynamic vegetation cover, we investigate vegetation- atmosphere feed-backs, and the amplifying impact of reduced vegetation cover on the Millennium Drought.

315

Is there a "speed bias" in eddy-covariance measurements at a fixed location? Laubach, Johannes1, McNaughton, Keith2

Presenting author’s e-mail: [email protected]

1Landcare Research, Lincoln, New Zealand 2Kerikeri, New Zealand

Session 5.3 – February 7, 2018, 1200-1215

The principle underlying the eddy-covariance method is that the covariance of the time series of a given variable with the time series of vertical wind speed, measured at a fixed location, is an unbiased estimate of the mean vertical flux of that variable across the flow field. Since measurements are taken at fixed time intervals, faster-moving regions of the flow are sampled less often than slower-moving regions. If slower and faster regions of the flow field contribute evenly to the vertical flux, then the eddy covariance will correctly represent the flux; however, if that is not the case then the flux estimate will be biased. We have developed the mathematical formalism to investigate whether such speed- induced biases occur and have applied it to selected datasets. We find that the first variables affected by this type of bias are the wind vector components themselves, and as a consequence, also the apparent mean tilt angle of the flow, i.e. the apparent streamline orientation. Therefore, the usually applied methods for coordinate rotation already require a correction. After application of a corrected rotation procedure, we then investigate the effect on the covariances of scalar variables with the corrected vertical wind component. In particular, we will determine to what degree the sum of sensible and latent heat fluxes is affected by speed-induced bias and whether that, in turn, can provide an explanation why this sum, when obtained with the standard version of the eddy-covariance method, frequently falls short of closing the surface energy budget.

316

Derived Optimal Linear Combination Evapotranspiration (DOLCE): a global gridded synthesis et estimate Hobeichi, Sanaa1,2, Abramowitz, Gab1,2, Evans, Jason1, Ukkola, Anna2

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, University of New South Wales, Sydney, Australia 2ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, Australia

Session 5.3 – February 7, 2018, 1215-1230

We detail a new monthly global gridded latent heat flux product that includes spatio-temporal uncertainty estimates. It is derived using a novel weighting method to combine six existing observationally-based latent heat products, constrained by observational data from 159 flux towers, in way that accounts for both performance differences and dependence between the constituent products. We show that the new latent heat product is in better agreement with tower based observations than ten different existing global latent heat datasets in a range of metrics, and therefore provides a valuable addition to currently available estimates. Ultimately, we plan to use the same methodology to develop monthly global gridded estimates of complete water and energy budgets. The new global estimates of water and energy budgets aim to provide a baseline estimate of surface partitioning of energy and water that will aid both model evaluation and process-based understanding.

317

Optimising Weather Research Forecast model performance by land-use change in the Southwest Western Australia D’Abreton, Peter1, Lam, Sean2,3, Pitts, Owen4

Presenting author’s e-mail: [email protected]

1envirosuite, QLD, Australia 2GHD, WA, Australia 3University of Western Australia, WA, Australia 4Air Assessments, WA, Australia

Session 5.3 – February 7, 2018, 1230-1245

The Weather Research Forecast (WRF) model is a numerical weather prediction system designed to serve both atmospheric research as well as operational forecasting needs (Skamarock, et al., 2008). The aim of this study is to assess the performance of the WRF model in predicting the complex meteorology in the south western corner of Australia.

The base case model for this study is defined as the default WRF terrain elevation and land-use data as well as default land-use property. A model sensitivity analysis was carried out by replacing the terrain and land use data with SRTM and MODIS data respectively. In addition, the MODIS data was further modified by satellite imagery at the inner most model domain. Also, the default land-use property tables were modified based on satellite product and other data sources to reflect representative Australian conditions.

A statistical approach was adopted to verify WRF performance by comparing hourly surface wind speed, wind direction and temperature predictions at the selected receptors against corresponding measurements at the receptor locations. A set of benchmarks for these parameters were set for mesoscale scale evaluation by Emery et al., (2001) and Tesche et al., (2001).

The results of this study show that WRF predicts the meteorology within acceptable levels in the south west corner of Australia. The sensitivity analysis demonstrates by refining the several parameters in the model system, the model performance can be significantly improved.

References:

Emery, C., Tai, E., & Yarwood, G. (2001). Enhanced Meteorological Modeling and Performance Evaluation for Two Texas Ozone Episodes”, report to the Texas Natural Resources Conservation Commission. Novato, CA: Environ International Corp.

Skamarock, W. C., Klemp, J. B., Dudhia, J., Gill, D. O., Barker, D. M., Duda, M. G., et al. (2008). A Description of the Advanced Research WRF Version 3. NCAR Tech., Note NCAR/TN-475+STR, 113 pp.

Tesche, T. W., McNally, D. E., Emery, C. A., & Tai, E. (2001). Evaluation of the MM5 Model Over the Midwestern U.S. for Three 8-Hr Oxidant Episodes. prepared for the Kansas City Ozone Technical Work Group, prepared by Alpine Geophysics, LLC, Ft. Wright, K.

318

Theme 6: Antarctic Science and cryosphere 6.1 Antarctic sea ice: variability, trends, and drivers Antarctic sea ice variability and associated changes in Southern Ocean cyclones and large-scale drivers Thorn, Dominic1, Simmonds, Ian1

Presenting author’s e-mail: [email protected]

1University of Melbourne, Vic, Australia

Session 6.1 – February 7, 2018, 1130-1145

In contrast to the Arctic region, which has seen rapid sea ice loss for the past 40 years, the Southern Ocean saw a steady growth in sea ice extent between 1979 and mid-2016, before a dramatic decline at the end of 2016. This initial growth has been widely attributed to the intensification of the Amundsen Sea Low associated with the positive polarity of the Southern Annular Mode (SAM). The total Antarctic trends mask significant regionality in sea ice trends. Here we show that increasing sea ice in the Ross and Amundsen Seas are linked with the SAM, as are winter and springtime decreasing trends near the tip of the Antarctic Peninsula, associated with increased westerly winds around the continent. Relationships with the El Nino Southern Oscillation (ENSO) were also examined. We found a dipole response in the sea ice concentration (SIC) correlation with the Nino 3.4 index. Positive correlations in the Bellingshausen Sea and negative correlations in the Ross and Amundsen Seas are consistent with a tropical SST influences on the Amundsen Sea Low (ASL). La Nina periods lead to a more intense ASL with expansion in the Ross and Amundsen Seas and contraction in the Bellingshausen Sea.

Using a cyclone tracking algorithm, we will diagnose and document changes in Southern Ocean cyclones since 1979. Surface winds are the dominant drivers of sea ice movement. Any changes in the frequency and intensity of cyclones will have implications for the ice field, particularly over short timescales. The ongoing ice retreat is likely linked with such changes.

319

Process-informed modelling of the sea ice floe size distribution Roach, Lettie1,2, Dean, Samuel1, Horvat, Christopher1,3, Smith, Madison4, Bitz, Cecilia4

Presenting author’s e-mail: [email protected]

1National Institute of Water & Atmospheric Research, Wellington, New Zealand 2Victoria University of Wellington, Wellington, New Zealand 3Harvard University, MA, United States 4University of Washington, WA, United States

Session 6.1 – February 7, 2018, 1145-1200

The lateral size of sea ice floes is receiving increasing attention as an important variable for the polar climate system. Sea ice floe size distributions, which can include floe sizes orders of magnitude smaller than the grid resolution, can now be simulated in global sea ice models. This allows inclusion of additional model physics, including alternative sea ice growth pathways and fracture of ice by ocean surface waves.

Floe size distributions are difficult to observe at sufficiently high resolution and sufficiently large spatial and temporal scales for global model validation. However, individual model processes can be observationally constrained. Here, we present results from a model-motivated observational study from images captured by wave buoys in the autumn Arctic Ocean.

These results inform our implementation of a joint sea ice floe size and thickness distribution in the Los Alamos sea ice model, CICE, coupled to a dynamic ocean. Our process-based approach to model development allows us to investigate the impacts of each process individually. We find a strong contribution of sea ice growth processes to power-law behaviour in the floe size distribution.

A key remaining question is whether such alterations to model physics affect larger-scale sea ice properties. We will present coupled model results that investigate this question, and discuss future possible work that may cause significant impacts on the polar climate system.

320

Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability Meehl, Gerald A.1, Arblaster, Julie M.1,2, Bitz, Cecilia M.3, Chung, Christine C.Y.4, Teng, Haiyan1

Presenting author’s e-mail: [email protected]

1National Center for Atmospheric Research, Colorado, U.S.A. 2Monash University, Victoria, Australia 3University of Washington, Washington, U.S.A. 4Bureau of Meteorology, Victoria, Australia

Session 6.1 – February 7, 2018, 1200-1215

Antarctic sea-ice extent slowly increased in the satellite record from1979 when the record began until 2014. From the late 1990s until around 2014, the increase accelerated, but the average of all climate models showed a decline. Meanwhile, the Interdecadal Pacific Oscillation, an internally generated mode of climate variability, transitioned from positive to negative around 2000, with an average cooling of tropical Pacific sea surface temperatures, a slowdown of the global warming trend, and a deepening of the Amundsen Sea Low near Antarctica that contributed to regional circulation changes in the Ross Sea region and expansion of sea ice. Here we show that the negative phase of the Interdecadal Pacific Oscillation (IPO) in global coupled climate models is characterized by anomalies similar to the observed sea-level pressure and near-surface 850 hPa wind changes near Antarctica from 2000 to 2014 that are conducive to expanding Antarctic sea-ice extent, particularly in the Ross Sea region in all seasons, involving a deepening of the Amundsen Sea Low. These atmospheric circulation changes are shown to be mainly driven by precipitation and convective heating anomalies related to the Interdecadal Pacific Oscillation in the equatorial eastern Pacific, with additional contributions from convective heating anomalies in the South Pacific convergence zone and tropical Atlantic regions. As the IPO transitioned to positive around 2014, subsequent retreat of Antarctic sea ice in late 2016 and early 2017 is shown to have had a contribution from convective heating anomalies associated with anomalous convection in the tropical eastern Indian Ocean.

321

Southern Hemisphere surface climate and ocean circulation response to Antarctic meltwater in a warming world Park, Wonsun1, Latif, Mojib1,2

Presenting author’s e-mail: [email protected]

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany 2University of Kiel, Kiel, Germany

Session 6.1 – February 7, 2018, 1215-1230

The Southern Hemisphere has seen prominent climate changes during the past decades that are not captured by climate models in historical simulations employing observed radiative forcing. One example is the cooling of the Southern Ocean sea surface temperature (SST) in large areas. Another example is the expanding Antarctic sea ice extent since the start of the satellite measurements. The historical simulations, however, do not incorporate the meltwater from the Antarctic ice sheet which is losing mass. Here we investigate by means of dedicated climate model simulations the potential role of this meltwater for the Southern Hemisphere (SH) surface climate and ocean circulation, an influence that also is ignored in most short-term and long-term climate change projections. When estimates of present and future Antarctic meltwater is incorporated in global warming simulations with rapidly increasing atmospheric carbon dioxide (CO2) concentration, SH surface warming and sea ice retreat is delayed by several decades relative to simulations without the meltwater. Further, the meltwater slows the Antarctic Circumpolar Current (ACC), which is gradually offset by the strengthening westerly surface winds developing in response to the increasing CO2. The ACC slowing due to the Antarctic meltwater may thus be an important factor when discussing the future evolution of the ACC. This study suggests that climate model projections for the 21st century could benefit from incorporating the meltwater from the Antarctic ice sheet.

322

On the role of the tropical Indian Ocean for the sharp decline of Antarctic Sea- Ice in austral spring 2016 Wang, Guomin1, Hendon, Harry1, Arblaster, Julie M.2,3

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Melbourne, VIC, Australia 2Monash University, Clayton, VIC, Australia 3National Center for Atmospheric Research, Boulder, Colorado, USA

Session 6.1 – February 7, 2018, 1230-1245

Over the past several decades (1979-2015) Arctic sea-ice cover has decreased but Antarctic sea-ice cover has increased. It is believed that both anthropogenic and natural variability contribute to the contrasting sea-ice variability at the two poles. However, during austral spring 2016 Antarctic sea ice extent (SIE) unexpectedly decreased sharply and reached record low values. We show a primary role for anomalous conditions in the tropical Indian Ocean and far western Pacific for promoting this rapid decline. In austral winter 2016, a very strong negative Indian Ocean dipole (IOD) developed in the tropical Indian Ocean, resulting in a record tropical convective tripole anomaly over the tropical Indian Ocean and western Pacific. This pattern of tropical convection acted as a Rossby wave source to generate a wave train that promoted favourable conditions for sea ice decline over the Pacific to west Ross Sea sector and the Bellingshausen Sea sector. A strong Madden-Julian oscillation (MJO) then traversed the Indian Ocean in November 2016, acting to temporarily suppress the anomalous convective tripole and Rossby wave train, but resulting in a low SAM response that accelerated sea ice declines in the Indian Ocean sector. Although the IOD primarily reflects internal variability of the tropical climate system, we will discuss how the ongoing warming trend in the Indian Ocean may influence these events in the future.

323

The highest temperature for the Antarctic continent: 1 Local-scale phenomena triggered by large-scale forcing Bozkurt, Deniz1, Rondanelli, Roberto1, Marin, Julio2, Garreaud, René1

Presenting author’s e-mail: [email protected]

1Department of Geophysics, University of Chile, Santiago, Chile 2Department of Meteorology, University of Valparaiso, Valparaiso, Chile

Session 6.1 – February 7, 2018, 1245-1300

A record high-temperature of 17.5°C with foehn conditions occurred on 24 March 2015 at the Esperanza research base located near the northern tip of the Antarctic Peninsula (AP). The event is analyzed using surface station data, satellite imagery and reanalysis data. MODIS Antarctic Ice Shelf Image Archive of Larsen B Ice Shelf illustrates a clear immediate trace of the foehn-melt mechanisms of ice coverage disintegration as well as melt ponds on the surface of the ice. ERA-Interim reanalysis shows an anomalous northwest southeast midlevel ridge and surface anticyclone stretching from South America to theAP, accompanied with an atmospheric river resulting in a warm and humid air advection toward the AP, and eventually triggered the foehn occurrence at Esperanza. A regional climate model (RegCM4) is used to disentangle the large-scale warm air advection and local topographically induced warming through a topography removal experiment over the AP. Topography removal experiment results in disappearance of local topographically induced warming along the eastern coast of the AP with the largest negative anomalies of

-12.5°C. Given the observed anomaly of +17.3°C at Esperanza station during th event, it could be stated that a large part of the warming anomaly (+12.5°C of +17.3°C) during the event could be attributed to foehn impact. The evidence of long-term and recent term trend changes in near-surface air temperature in the lee side and low-level zonal wind speed and vapor transport in the upwind side highlights that local-scale forcing triggered by large-scale forcing may play a key role in the occurrence of extreme temperature events over the AP.

324

6.4 Antarctic science Atmospheric influences on the anomalous 2016 Antarctic sea ice retreat Raphael, Marilyn1, Schlosser, Elisabeth2, Haumann, Alexander3

Presenting author’s e-mail: [email protected]

1University of California Los Angeles, CA, United States 2Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, Austria 3Center for Climate Systems Modeling, ETH Zurich, Switzerland

Session 6.4 – February 7, 2018, 0930-0945

Over the past three decades, a small but significant increase in sea ice extent (SIE) has been observed in the Antarctic. However, in 2016 there was a surprisingly early onset of the melt season. The maximum Antarctic SIE was reached in August rather than end of September, and was followed by a rapid decrease. The decline of the sea ice area (SIA) started even earlier, in July. The retreat of the ice was particularly large in November where Antarctic SIE exhibited a negative anomaly (compared to the 1981-2010 average) of almost 2 Mio. km2, which, combined with reduced Arctic SIE, led to a distinct minimum in global SIE. And, satellite observations show that from November 2016 to February 2017, the daily Antarctic SIE has been at record low levels. We use sea level pressure and geopotential height data from the ECMWF- Interim reanalysis, in conjunction with sea ice data obtained from the National Snow and Ice Data Centre (NSIDC), to investigate possible atmospheric influences on the observed phenomena. Indications are that both the onset of the melt in July and the rapid decrease in SIA and SIE in November were triggered by atmospheric flow patterns related to a positive Zonal Wave 3 index, i.e. synoptic situations leading to strong meridional flow. Additionally the Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. It is likely that the SIE decrease was preconditioned by the SIA decrease. Positive feedback effects led to accelerated melt and consequently to the extraordinary low November SIE.

325

Large-scale forcing of the Amundsen Sea low and its influence on sea ice and west Antarctic temperature Clem, Kyle1, Renwick, James2, McGregor, James2

Presenting author’s e-mail: [email protected]

1Rutgers, The State University of New Jersey, New Brunswick, New Jersey, USA 2Victoria University of Wellington, Wellington, New Zealand

Session 6.4 – February 7, 2018, 0945-1000

Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño- Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent.

326

Studying green and blue icebergs of marine ice to better understand ice-shelf basal processes Warren, Stephen1, Heil, Petra2, Roesler, Collin3, Fitzpatrick, Mel4, Brandt, Richard5

Presenting author’s e-mail: [email protected]

1University of Washington (Seattle), Washington, USA 2Antarctic Division, Tasmania, Australia 3Bowdoin College, Maine, USA 4Independent, Tasmania, Australia 5University at Albany, New York, USA

Session 6.4 – February 7, 2018, 1000-1015

Supercooled seawater accretes to the base of several Antarctic ice shelves. For example, in parts of the Amery Ice Shelf, frozen seawater contributes up to one-third of the ice-shelf thickness. Many of the icebergs produced by the Amery are therefore composite icebergs; the upper part consists of meteoric glacier ice from snowfall, but the lower part is frozen seawater (marine ice). When these icebergs capsize, the marine ice is exposed to view; it can be accessed for study in springtime when the icebergs are embedded in shorefast sea ice. The marine ice varies in colour from blue to green depending on the content of dissolved organic matter. The colour is therefore an indicator of biological productivity in the seawater from which the ice froze.

To infer processes at the ice-shelf base, these icebergs may be examined for spectral reflectance, hydrogen and oxygen isotopes, organic matter, particles, and distribution of cracks and stripes. Seasonal and interannual variations may be quantified from samples collected along the marine ice- growth trajectory at the meteoric/marine-ice interface. The scale of small turbulent eddies at the ice- shelf base, which govern the transfer of heat between ocean and ice, can be inferred from the size of scallops in the iceberg surface. Dark stripes within meteoric ice result from tension-cracks at the grounding line, forming basal crevasses that fill suddenly with seawater; their width, spacing, and salinity can give clues to processes at the grounding line. Results will be shown from icebergs sampled on Australian expeditions near Davis and Mawson stations.

Marine ice is more readily accessed by sampling an iceberg than by drilling through an ice shelf; investigation of icebergs can guide future coring of ice shelves. Warming of Antarctic intermediate water is expected to cause a declining trend in the abundance of marine-ice icebergs.

327

Ocean-sea ice interactions in the Southern Ocean in CMIP5 models Schroeter, Serena1,2,3, Hobbs, Will3,2, Bindoff, Nathaniel L.1,3,2

Presenting author’s e-mail: [email protected]

1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7004, Australia 2Australian Research Council Centre of Excellence for Climate System Science (ARCCSS), Hobart, 7004, Australia 3Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), Hobart, 7004, Australia

Session 6.4 – February 7, 2018, 1015-1030

Heat exchange between the atmosphere and the Southern Ocean contributes at least half the energy required to melt Antarctic sea ice during the retreat season. Additional heat entering the oceanic mixed layer through upwelling or lateral flow can enhance this heat exchange and the resulting spring melt. However, modelled stratification of the upper ocean from increased sea ice melt has been shown to suppress convective overturning and upward heat transport, promoting enhanced production of sea ice during the subsequent growth season. To examine the interactions between Antarctic sea ice and the oceanic mixed layer, we calculate a surface heat budget in seven CMIP5 models, comprising sea ice production and melt, radiative and turbulent heat fluxes, and changes to the ocean heat content in the mixed layer. This isolates the contribution of additional heat entering the mixed layer, and the implications for simulated Antarctic sea ice production and melt.

328

Future projections of Antarctic ice shelf melting Naughten, Kaitlin1,2,3, Meissner, Katrin1,2, Galton-Fenzi, Ben4,3, England, Matthew1,2, Timmermann, Ralph5, Hellmer, Hartmut5

Presenting author’s e-mail: [email protected]

1Climate Change Research Centre, University of New South Wales, NSW, Australia 2ARC Centre of Excellence for Climate System Science, Australia 3Antarctic Climate and Ecosystems Cooperative Research Centre, TAS, Australia 4Australian Antarctic Division, TAS, Australia 5Alfred Wegener Institut, Germany

Session 6.4 – February 7, 2018, 1030-1045

Antarctic ice shelves are crucial for the stability of the land-based Antarctic Ice Sheet, and therefore have an important role to play regarding sea level rise over the coming centuries. However, ice shelf cavities were not included in any of the CMIP5 (Coupled Model Intercomparison Project phase 5) models simulating future projections of the climate system. Here we instead force FESOM (Finite Element Sea-ice/Ice-shelf Ocean Model), a global ocean model including ice shelf cavities, with bias- corrected atmospheric output from CMIP5 projections to assess the impact of potential 21st-century climate change on ice shelf melt rates. We present five experiments, consisting of two future climate scenarios (RCP 4.5 and 8.5) and two choices of CMIP5 models (multi-model mean and ACCESS 1.0) as well as a parallel control experiment with repeated 1992-2005 forcing. Our simulations show increased ice shelf melting in response to climate change, in all sectors of Antarctica. In most regions, stronger melting is due to a warmer ocean surface in summer, which causes seasonal melting at ice shelf fronts. A different process drives increased basal mass loss in the Amundsen Sea sector, which experiences intrusions of warm Circumpolar Deep Water in all but one future scenario due to stratification of the water column from reduced sea ice formation. This reverses the model’s present- day cold ocean bias in the region, and causes total basal mass loss from Pine Island Glacier Ice Shelf to increase by a factor of 2 to 4. Apart from the impacts of climate change on ice-shelf/ocean interaction, we also assess simulated changes in sea ice cover, continental shelf water mass properties, and ACC transport.

329

Ablation of sloping ice-shelf at Antarctic Conditions Mondal, Mainak1, Gayen, Bishakhdatta1

Presenting author’s e-mail: [email protected]

1Australian National University, ACT, Australia

Session 6.4 – February 7, 2018, 1045-1100

Precise estimation of the ablation rate at the marine terminating ice-tongues, which are vulnerable to present climate trend, is necessary for the future projection of the sea level rise and global climate. Most of the regional and global scale models can not resolve the boundary layer processes and use turbulent-parameterisation to infer the melting at the ice-ocen interface based on far field conditions. We perform turbulence resolving simulations to model the melting under a sloping ice-shelf with uniform ambient flows varying over the range 0.05 - 0.15 m/s. The far field salinity is fixed at 35 psu while far field temperature is varied over -1° - 1°C, representing Antarctic condition. Effect of both convection and ambient flow on the rate at the ice-ocean interface are examined. The results show that, beyond a threshold value, the melt rate is sensitive to the background stress and follows a power law which is well predicted by theoretical estimate. These results can be used to improve the parameterisation scheme for the large scale ocean models.

330

Theme 7: Climate services and Community engagement 7.1 Weather and climate in the media AND 7.2 Education and outreach Cutting to the Chase: Climate Change Communication Rice, Martin1, Hay, Nick2

Presenting author’s e-mail: [email protected]

1Climate Council of Australia, NSW, Australia 2Climate Council of Australia, VIC, Australia

Session 7.1/7.2 – February 9, 2018, 1130-1140

Climate change is the biggest threat facing humanity, yet there are significant challenges to ensuring that official organisations communicate important and reliable climate information to the public. Over the last five years the climate change landscape has changed significantly. While the discussion used to focus on future consequences, we now have significant data about the immediate impacts of climate change on human health, property, infrastructure, agriculture and biodiversity today. Climate change is influencing extreme weather events and some of the most severe climate impacts the world has experienced have occurred in 2016; global action has accelerated with the global energy giants, China, Europe and the USA leading; and the price of renewable energy has dropped quickly enabling rapid increases in capacity in solar PV and wind power. Despite these shifts climate change remains a communications challenge. For decades there has been a concerted campaign of misinformation that has confused the public. Many of the myths remain potent and must be combatted. Additionally, climate change has predominantly been a highly complex and abstract discussion of science, policy and the economy. Making climate change information relevant, interesting and engaging for the general public is an on-going challenge for communicators. In Australia, after years of toxic public discussion focused on the carbon price, the conversation on climate change is shifting. Recent polling consistently shows that public concern is increasing, particularly after record-breaking years of global temperatures and extreme weather in Australia. Using the Climate Council as a case study, as well as psychology and public opinion research in Australia and abroad we provide a simple framework to communicate climate change information effectively.

331

Observing and Predicting the 2015-16 El Niño L’Heureux, Michelle1, Takahashi, Ken2, Watkins, Andrew B3, Barnston, Anthony G4, Becker, Emily J1, Di Liberto, Tom E1, Gamble, Felicity3, Gottschalck, Jon1, Halpert ,Michael S1, Huang, Boyin5, Mosquera- Vasquez, Kobi2, Wittenberg, Andrew T6

Presenting author’s e-mail: [email protected]

1NOAA/NWS/NCEP/Climate Prediction Centre 2Instituto Geofisico del Peru (ENFEN-Peru) 3Bureau of Meteorology, Australia (BoM) 4IRI, Columbia University 5NOAA/National Centers Environmental Information 6NOAA/Geophysical Fluid Dynamics Laboratory

Session 7.1/7.2 – February 9, 2018, 1140-1150

The 2015-16 El Niño was arguably the most widely anticipated El Niño-Southern Oscillation (ENSO) event, and it was preceded by nearly four decades of advancements in observing and prediction systems. While rivalling the major El Niño events of 1982-83 and 1997-98, the 2015-16 event was the first major El Nino to be analysed in almost real time through the web and social media.

The ENSO cycle is a leading source of seasonal climate variability and predictability, and thus it is closely monitored by many organisations around the world. The authorship of this paper is composed of individuals associated with three national-level climate agencies (NOAA, BoM, ENFEN-Peru).

Comparisons are made with the 1997-98 and 1982-83 El Niño events, with the 2015-16 El Nino showing a stronger response in some ENSO indices (western tropical Pacific surface and sub-surface temperatures) but weaker in others (trade winds and outgoing long-wave radiation).

The benefits and pitfalls of tracking an El Niño in the digital age are assessed; the increased ease and speed of communication via social media made sub-monthly updates possible, but was offset by the implication that ENSO evolves at a rapid speed rather than over a period of months. Also, the availability of daily and weekly data relating to ENSO characteristics such as sea surface temperature, while of benefit to climate prediction agencies, also made possible the identification of short term fluctuations by non-climate professionals as being significant ENSO signals.

This paper also summarises the collective experience among climate agencies in tracking the observational evolution, verifying model forecasts and documenting global climate anomalies associated with the 2015-16 El Niño.

332

Communicating links between climate change and extremes Torok, Simon1, Holper, Paul1, Hassol, Susan2, Lewis, Sophie3

Presenting author’s e-mail: [email protected]

1Scientell Pty Ltd 2Climate Communication 3Australian National University

Session 7.1/7.2 – February 9, 2018, 1150-1155

The science of attributing extreme weather and climate events has progressed in recent years to enable an analysis of the role of human causes while an event is still in the media. However, there is widespread confusion about the linkages between human-induced climate change and extreme weather, not only among the public, but also among some meteorologists and others in the scientific community.

Communicating links between climate change and extremes can be made clearer by, for example, leading with what the science does understand, using metaphors to explain risk and probabilities, using accessible language for conveying uncertainty and confidence, while avoiding loaded terminology and language that creates a sense of hopelessness.

This presentation will include guidelines for clear communication on extremes, drawing on Hassol et al. (2016) and from experience disseminating controversial science information through brochures, books, web sites and an app.

Reference:

Hassol, S. J., S. Torok, S. C. Lewis, and P. Luganda, 2016: (Un)Natural Disasters: 398Communicating the Linkages Between Extreme Events and Climate Change. WMO 399Bulletin, 65, 2–9. https://public.wmo.int/en/resources/bulletin/unnatural-disasters-communicating-linkages- between-extreme-events-and-climate

333

An analysis of climate and weather in the media Holper, Paul1, Torok, Simon1, Power, Scott2

Presenting author’s e-mail: [email protected]

1Scientell Pty Ltd 2Bureau of Meteorology

Session 7.1/7.2 – February 9, 2018, 1155-1200

Climate, climate change and weather are topics of enduring interest to society and the media. There have been a number of assessments of the frequency of mentions in the media over time of terms such as ‘climate change’ (eg Boykoff & Boykoff 2007, Power et al 2008, Schmidt et al 2013) and internet searches for terms such as 'weather' (Power and Delage 2011).

This presentation will compare the frequency of occurrence of 'weather', 'climate change' and a range of other ‘AMOS-relevant’ terms in the Australasian media. The analysis will cover both print and electronic media. It has been undertaken via the international media monitoring service, Meltwater, which tracks over 13,000 media representatives in Australia and New Zealand. We will identify seasonal cycles, trends and spikes and suggest how these features arise. The analysis will be augmented by analysing internet searches over longer periods. We will also examine the frequency and timing of articles exhibiting denialist views.

Our conclusions will include tips to maximise media coverage of climate and weather topics, including targeting specialist journalists in a rapidly-changing media landscape, crafting relevant hooks and media releases, and consideration of non-traditional media campaigns.

References:

Boykoff, M.T. and Boykoff, J.M., (2007). Climate change and journalistic norms: A case-study of US mass-media coverage. Geoforum, 38(6), pp.1190-1204.

Power, S.B., and Delage, F., (2011). Sumer Peak, winter minimum, and growth in the demand for online weather services in Australia. Bull. American. Meteorol. Soc., 1275-1277.

Power, S.B., Plummer, N., Pearce, K.B., Walland, D., Edwards, S., Jones, D., Gipton, S., Holper, P.N. and Whitehead, R., (2008). Changes in Australian attitudes towards global warming. WMO MeteoWorld, April issue.

Schmidt, A., Ivanova, A., & Schäfer, M. S. (2013). Media attention for climate change around the world: A comparative analysis of newspaper coverage in 27 countries. Global Environmental Change, 23(5), 1233-1248.

334

Comparing weather prediction information between formal and informal sources Hewson, Michael1, Ames, Kate1

Presenting author’s e-mail: [email protected]

1CQUniversity, QLD, Australia

Session 7.1/7.2 – February 9, 2018, 1200-1208

Weather prediction and emergency service agencies increasingly need to account for the “enthusiast” in the ranks who are seen as pseudo-official sources by members of the public. During disaster events, disseminating credible information is vital, but recent events suggest there are issues of trust in weather-based information generally. This project explores the accuracy of information provided to inform the public during the flood event in South East Queensland post Cyclone Debbie in March 2017. Severe category 4 tropical Cyclone Debbie had crossed the coast near Airlie beach on the Queensland coast. On its inland track back out to sea south of Brisbane, Debbie’s precipitation created devastating floods in the Fitzroy River basin and through-out SE-Queensland and northern NSW.

This project aims to identify the accuracy and timeliness of prediction information dissemination to the public via official weather sources as opposed to unofficial weather sources via social media.

The study will assist authorities improve analysis and communication processes accounting for changes afforded by social media.

The research is based on critical social enquiry to document and analyse emergency weather warnings from official sources and compare these with educated enthusiasts disseminating information via social media. This is a mixed method study.

To determine whether the event was in fact misdiagnosed by official channels, Bureau of Meteorology data taken from sites in South East Queensland on Thursday 23 March will be analysed. Automatic weather station, rain rate radar imagery and geo-stationary Himawari satellite data will be processed. This analysis will be compared against official warnings for South East Queensland on Wednesday 22 and Thursday 23 March. Content analysis of social media website Higgins Storm Chasing for those dates will provide a basis for comparison between official warnings and commentary by unofficial sources.

335

Bearing witness 2017: Fiji climate change journalism revisited Robie, David1, Chand, Sarika2

Presenting author’s e-mail: [email protected]

1Auckland University of Technology, New Zealand 2The University of the South Pacific, Fiji

Session 7.1/7.2 – February 9, 2018, 1208-1215

In February 2016, the Fiji Islands were devastated by Severe Tropical Cyclone Winston, the strongest recorded tropical storm in the Southern Hemisphere. The category 5 storm with wind gusts reaching 300 kilometres an hour, left 44 people dead, 45,000 people displaced, 350,000 indirectly affected, and $650 million worth of damage (Climate Council, 2016). In March 2017, the Secretariat of the Pacific Regional Environment Programme (SPREP) launched a new 10-year Strategic Plan 2017-2026, which regards climate change as a ‘deeply troubling issue for the environmental, economic, and social viability of Pacific island countries and territories’. In November, Fiji will co-host the UN Framework Convention on Climate Change (COP23) climate change conference in Bonn, Germany. Against this background, the Pacific Media Centre despatched two neophyte journalists to Fiji for a two-week field trip in April 2016 on a ‘bearing witness’ journalism experiential assignment to work in collaboration with the Pacific Centre for Environment and Sustainable Development (PaCE-SD) and the Regional Journalism Programme at the University of the South Pacific. This article is a case study assessing this climate change journalism project and arguing for the initiative to be funded for a multiple-year period in future and to cover additional Pacific countries, especially those so-called ‘frontline’ climate change states.

336

Newspaper coverage of climate change in Fiji: a content analysis Chand, Sarika1

Presenting author’s e-mail: [email protected]

1The University of the South Pacific, Fiji

Session 7.1/7.2 – February 9, 2018, 1215-1223

Media plays a crucial role in the global fight against climate change, acting as a tool for awareness, advocacy and policy change. For Fiji, this role becomes even more essential with the country’s vulnerable island system facing the direct impact of current and future climate change threats. The primary aim of this study was to analyse climate change coverage in the Fiji press. The Fiji Times, Fiji’s national newspaper, was examined to identify trends in climate change coverage between January 2004 and December 2010. A quantitative analysis was initially carried out to see the volume of reports, followed by a qualitative look into the context and thematic values of the news reports. Empirical findings showed an increase in coverage over time, although there was a transiency in the high levels of coverage when looked at on a monthly basis. Published reports also show a trend of event-based reporting with more than 80 percent of articles being generated out of or following up on a climate change convention, meeting or report launch. An overall consensus on the scientific realities of climate change in the newspaper coverage, and relatively high coverage of impacts and threats of climate change highlighted the plight of the islands. Reporting of climate change issues needs to be prioritised if the press is to fulfill its role in providing timely information on climate change. Journalists training and collaboration with national stakeholders would assist in more effective climate change coverage instead of the great reliance on one-off events to spark recognition of the major environmental problem. Developments in the discourse since this research was conducted will be worth noting as climate change has continued to rise as one of the most salient global environmental issues of our time.

337

Life cycle assessment in interdisciplinary education of sustainability, energy and green economics Sikand, Monika1, Mazzatenta, Claudio1, Wong, Keith1, Socha, Aaron2

Presenting author’s e-mail: [email protected]

1Bronx Community College, City University of New York, New York, USA 2Queens University of Charlotte, North Carolina, USA

Session 7.1/7.2 – February 9, 2018, 1223-1230

This study demonstrates the life cycle assessment of a product in interdisciplinary student centered pedagogy in Sustainability, Energy and Green Economics. This interdisciplinary teaching model was used to introduce inquiry based pedagogy in student’s environment literacy, understanding on how the principles of sustainability are building the green economy and encourage students to apply the critical lens of sustainability to all aspects of their personal lives, as well as local, regional and global economies. It is shown that an interdisciplinary approach to introduce students to the foundations of sustainability strongly connects education with real world applications, and highlights the growing influence of sustainable practices on the world at large. The authors will present results from the interdisciplinary course “Sustainability, Energy and Green Economy” taught at the Center of Sustainable Energy, Bronx Community College, City University of New York (CSE-BCC-CUNY) by faculty from Physics, Chemistry, Biology. The students enrolled in this course are lead through the concept of ‘Life Cycle Analysis’ and how such analyses can be used to create market value and a “green product”. The students chose a product of their choice, collected data of raw materials, provided carbon foot print calculations, investigated impact of such a product on health and environment, engaged in discussion of results, review of other student’s work and articulated a hypothesis specifically related to the sustainability of societal and economic market trends. The final assessment resulted in paper submission on Life cycle analysis of a product chosen by students. The qualitative research methods including course surveys and questionnaires provided evidence that the inquiry based, student centered, interdisciplinary pedagogy improves student perception, relevance and environment literacy to understand the principles of sustainability in comprehensive life cycle assessment of a certain product.

338

Researcher development in the ARC Centre of Excellence for Climate Extremes Hart, Melissa1

Presenting author’s e-mail: [email protected]

1ARC Centre of Excellence for Climate System Science, UNSW

Session 7.1/7.2 – February 9, 2018, 1230-1238

The Researcher Development program within the new ARC Centre of Excellence for Climate Extremes recognizes that development and training should not end as soon as you submit your PhD. The Researcher Development program will include fundamental research and communication skills, professional development, mentoring and leadership opportunities and will involve ALL Centre researchers. Climate scientists come from a variety backgrounds with a varying range of skills and knowledge. Therefore, components of the Program will be tailored to individual researcher needs. Incoming researchers will undertake an individualised training needs analysis to assess their skills and knowledge base, and prepare an individualised career development plan. This will reveal the skills and knowledge they need to acquire for successful research and to prepare for their future careers.

Nest within the Researcher Development program is a program of tailored research training for postgraduate and honours students which forms our Graduate Program. An individualised training plan will be developed for each student. This training plan will become a living document revisited throughout the student’s candidature. The targeted training offered through the Graduate Program will allow students to acquire the skills they need to optimise their research and research outputs, including publications, to ensure an on time and successful completion.

339

The Sydney Schools Weather and Air Quality (SWAQ) Network Hart, Melissa1,2, Maharaj, Angela M.1,2, Di Virgilio, Giovanni2

Presenting author’s e-mail: [email protected]

1ARC Centre of Excellence for Climate System Science, UNSW Sydney, Australia 2Climate Change Research Centre, UNSW Sydney, NSW, Australia

Session 7.1/7.2 – February 9, 2018, 1238-1245

Sydney’s population is predicted to grow by 30% within twenty years, most of which is slated for the semi-rural fringes. The resulting urbanisation could adversely impact temperature and air quality in these areas of rapid population growth. Currently, meteorology and air quality measurement sites to adequately monitor the effects of increased urbanisation on local weather and air quality are located sparsely. This citizen science project funded by the Australian Government’s Department of Industry, Innovation and Science, will place meteorology and air quality sensors in approximately 30 schools across Sydney. Students will collect and analyse research quality data for use in science and geography curriculum-aligned classroom activities. The data will also be freely available online to the public and researchers. This talk will report on how the siting of stations and recruitment of schools will be carried out for the first phase of the project.

340

How leadership skills can help us become better scientists: Lessons from Antarctica Speirs, Johanna1,2, Hart, Melissa3

Presenting author’s e-mail: [email protected]

1Snowy Hydro Ltd, NSW, Australia 2School of Earth and Environmental Science, The University of Queensland, QLD, Australia 3ARC Centre of Excellence for Climate System Science, University of New South Wales, NSW, Australia

Session 7.1/7.2 – February 9, 2018, 1245-1253

Our changing planet is challenging scientist’s capabilities to lead, collaborate, communicate and influence policy and decision making. However, scientists are not often equipped with specialised training in these areas. The authors are participants in ‘Homeward Bound’ - a ground breaking leadership and strategic initiative for women in science. Launched in 2016, Homeward Bound aims to equip 1000 women in science, from all over the world, with the leadership, strategy and communication skills required to contribute to a more sustainable future. Participants undertake a year-long leadership program, culminating in intensive training on board a ship in Antarctica. The leadership content involves coaching and diagnostic testing on personal learning styles, attitudes, behaviours and emotional intelligence. Participants learn and understand what they’re doing well, but also pinpoint what they need to improve to become more effective communicators, collaborators and leaders. Participants explore their personal values and purpose and fine-tune a personal strategy to have a greater influence and impact in addressing complex problems in their field of study. Homeward Bound focusses on women due to the under-representation in global leadership and decision-making positions, however, leadership training could help us all. In this presentation, the authors share their experiences of the Homeward Bound program and discuss why it’s becoming critical that more of our scientific community equip themselves with effective leadership skills.

341

Ambassadors for science Whitaker, Richard1

Presenting author’s e-mail: [email protected]

1AMOS, NSW, Australia

Session 7.1/7.2 – February 9, 2018, 1253-1300

Possibly at no other time since 1616, when Galileo was accused of heresy, has science come in for so much public scrutiny and criticism as we have seen in the last 20 years. To a certain extent we, as scientists, have been unprepared for such a challenge and considerable inroads have been made against our public credibility during this time.

However there is much we can do as individual scientists to help retrieve this situation, with one such activity being that of public science education, sometimes called Education and Outreach – the subject of this special session.

In this presentation the author reveals the results of his community engagement history since July 2011, a period during which more than 150 public groups have been addressed on various weather and climate topics. The groups concerned include, Probus, Rotary, Lions, University of Third Age, historical societies and schools.

He has found that the general public is fascinated by science and is in fact “hungry” for general interest scientific knowledge. When the “big picture” of weather prediction and climate science is explained, audiences tend to become strongly engaged, a point well illustrated by the numerous appreciative references that have been received.

The author argues that doing good science at academic level is no longer enough – unless we can effectively and directly communicate our work to the public – who finance much of our endeavour, we run the risk of our labours being devalued by outside interests. In other words we should become ambassadors for science.

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7.3 Climate services for decision makers The high value and short payoff time of seasonal forecasts in risk-averse crop management McIntosh, Peter C.1, Brown, Jaclyn N.2, Asseng, Senthold3, Wang, Enli4

Presenting author’s e-mail: [email protected]

1CSIRO Oceans & Atmosphere, GPO Box 1538, Hobart 7001 Australia 2CSIRO Agriculture and Food, 15 College Rd, Sandy Bay, 7005 Australia 3Department of Agricultural & Biological Engineering, University of Florida, Gainesville, FL 32611, USA 4CSIRO Agriculture and Food, GPO Box 1666, Canberra ACT 2601, Australia

Session 7.3 – February 7, 2018, 0930-0945

Determining the appropriate amount of nitrogen fertilizer to apply in dry land cropping is a crucial decision for profit and productivity – too much nitrogen is an unnecessary cost, while too little will not allow the full yield potential to be realized, particularly in good years. Previous case studies in Western Australia suggest that harnessing current climate model forecasting capability to inform N fertilizer inputs can lead to a benefit of over A$50/ha. Here we explore whether this same benefit can be realized in eastern Australia. Using a climate forecast may increase the level of risk in years when the forecast is wrong, which may be unacceptable to the farm manager. To quantify the level of risk we introduce a range of metrics including “pay-off time”. We find that case studies in eastern Australia demonstrate increased average profits from using a seasonal rainfall forecast; ranging from A$16 to A$80 /ha over the study sites. Unlike the west however these profits are achieved in many cases with less risk to the farming system. In one location most of the profit was made in eight years of ten. A rainfall forecast allowed this same level of profit to be made in just four. We envisage that these risks will decrease with increasing skill in seasonal climate models in the future.

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Seasonal climate outlooks: keeping the customer satisfied Keay, Kevin1, Watkins, Andrew2

Presenting author’s e-mail: [email protected]

1Bureau of Meteorology, Australia 2Bureau of Meteorology, Australia

Session 7.3 – February 7, 2018, 0945-1000

The Bureau of Meteorology with Federal Government support is undertaking a four year program of work to improve its climate outlooks and introduce a series of climate model upgrades. As part of this work, known as the Improved Seasonal Forecasting Service (ISFS), the Bureau consulted directly with climate sensitive industries between August 2015 and June 2016 to understand their needs, and to guide priorities for improvement. Engaging and understanding user needs is considered critical to service development at the Bureau.

For instance, the workshops revealed that users have a strong preference towards chance of exceeding a user selected threshold (e.g. chance of exceeding X mm of rainfall or Y °C, chance of 100 hours below 20°C etc.) and chance of extremes outlooks (e.g. chance of heatwave, chance of heavy rainfall, chance of frost). This reflects quite a departure on past practices which have tended to emphasise probabilities attached to large groups such as terciles.

The service improvements to be delivered include:

• More localised climate outlooks using an upgraded model, Australian Community Climate and Earth-System Simulator-Seasonal (ACCESS-S), which replaces the Predictive Ocean Model for Australia (POAMA) (model resolution will increase from 250km to 60km). • More accurate climate outlooks, providing users with more confidence when making climate sensitive decisions. • Additional outlooks to cover the two to four week timeframe (filling the gap between the current 7-day weather forecast and the monthly and seasonal climate outlooks). • Additional changes are being made to the way forecast products are produced, including the introduction of full distributions based on ensembles and introduction of downscale information at 5km resolution.

The presentation will describe progress to date, including and plans for the remainder of the project.

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Climate Change Services: online tools that meet the needs of users…or not: Climate Change in Australia User Surveys 2016 - 2017 Clarke, John1, Hennessy, Kevin1, Gibb, Kerry1, Pearce, Karen2

Presenting author’s e-mail: [email protected]

1CSIRO Climate Science Centre, Aspendale, Vic, Australia 2Bloom Communication, Bathurst, NSW, Australia

Session 7.3 – February 7, 2018, 1000-1015

The CSIRO Climate Science Centre is building on its 30-year history of delivering climate change services within Australia and beyond. In 2015, the Climate Change in Australia (CCIA) website (www.climatechangeinaustralia.gov.au) was launched, providing the most comprehensive Australian climate change projections to date.

Ensuring the accessibility and applicability of climate change science and services is a focus of the National Environmental Science Programme Earth Systems and Climate Change Hub, which undertook a survey of CCIA users in July 2017 to evaluate how well the website and products meet users’ needs. This survey follows an initial user survey conducted in March 2016.

In 2016, there were 780 registered users, and 99 surveys were returned. In 2017, there were 1675 registered users and 128 surveys were completed. The 2017 survey repeated the 2016 survey questions for comparison. Questions focussed on who is using the website, which products were useful, the amount of user engagement and support, the applicability of the information, and what works well or could be improved. The 2017 survey also had four additional questions.

Whilst most users across both surveys identified as “Researchers” in the eastern States of Australia, almost 5% were international. Between 2016 & 2017, there was a reduction in users identifying as “Policy Analyst/Advisor” (12% to 6%). The proportion of respondents identifying as “end users” (as opposed to “next users” or “generators”) of climate information doubled to 40% in 2017.

Both surveys show consistent satisfaction with the usefulness of the website content. Across both surveys, around 70% of respondents indicated satisfaction with the web-tools.

While most respondents indicated satisfaction with user engagement and support, 2017 showed a reduction in those reporting “very good” engagement and support.

In 2017, the great majority of users used CCIA for “Impact assessment” (64%), “Adaptation planning” (58%) and “Awareness raising” (38%). There is a growing desire for more simplified communication.

The survey results will be used to inform enhancements to the CCIA projections products and services.

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Useful and usable information delivery for coastal adaptation Palutikof, Jean1, Rissik, David1, Webb, Steve1, Tonmoy, Fahim1, Leitch, Anne1, Boulter, Sarah1

Presenting author’s e-mail: [email protected]

1National Climate Change Adaptation Research Facility, Griffith University, Gold Coast Campus, Southport, Queensland 4222, Australia

Session 7.3 – February 7, 2018, 1015-1030

CoastAdapt is a decision support and information delivery framework for coastal managers in Australia seeking to understand and adapt to the risks from climate change and sea-level rise. It delivers widely ranging information and guidance, including climate and sea level scenarios at local council level through to 2100, how to build a business case, and jurisdictional differences in planning legislation. The first version was built between October 2014 and February 2017. The greatest challenge was to ensure that CoastAdapt is both useful and usable for its target audience, sited mainly in coastal local councils and small businesses. To meet this goal, the framework had to address very different user needs, from councils with very little knowledge of climate change and the associated risks, through to managers seeking to transition their adaptation plans into action. Failure would mean that CoastAdapt would cease to be used very soon after completion – a fate of very many decision support tools. To fully understand user needs, we engaged with and consulted potential users at every step, from initial design through the build process to evaluation after completion. The presentation will discuss the successes and failures of these consultation processes. Challenges exist in understanding and addressing user needs, for example, for most coastal managers climate change and sea-level rise risks are a low priority amongst their day-to-day activities. Information must be delivered efficiently to users who are time poor, and must precisely target their needs. CoastAdapt must be up-to-date and seen to be such, not only in scientific terms but also in terms of the legislative and regulatory framework within which adaptation takes place. The problems of ensuring that CoastAdapt will continue to be used and useful over time will be discussed.

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NextGen Projections: planning for the next generation of national climate projections in Australia Grose, Michael1, Moise, Aurel2, Evans, Jason3, Colman, Rob2, Clarke, John1, Brown, Josephine2

Presenting author’s e-mail: [email protected]

1CSIRO Oceans and Atmosphere, Hobart Australia 2Bureau of Meteorology, Melbourne Australia 3University of New South Wales, NSW Australia

Session 7.3 – February 7, 2018, 1030-1045

The NextGen Projections workshop brought together a targeted group of researchers from the climate projections field for two days in November 2017 to discuss a range of topics on where national climate projections could and should go in the coming years. There are continual developments in the science of understanding, modelling and projecting the climate. The upcoming IPCC sixth assessment report will be a major milestone on the global landscape, and there will be strong interest in what the assessment means for Australia. There are also major new data sources on the horizon, including the CMIP6 climate model database, the CORDEX regional downscaling experiment, and numerous others that can all be drawn upon for making climate projections. However, along with the new science and models, we also need to consider how the products and services can be enhanced to better meet the ever-evolving list of uses and users of climate projections to inform a widening range of applications. The workshop considered the perspectives of international experiences, previous projections producers, projections users, climate change detection and attribution and the emerging field of multi-year to decadal prediction. The workshop weighed up and debated various ideas and options for robustly understanding, framing and communicating information about the uncertain future climate, to enhance our shared national benefit. Here we give a report about the workshop, the outcomes and the next steps for continuing the conversation.

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Bellon, Gilles · 173 A Benthuysen, Jessica · 18, 57 Bernardo, Piero · 51 Beron-Vera, Francisco · 63 Abele, Doris · 29 Bers, Valeria · 29 Abellán, Esteban · 44 Beyer, Kathleen · 199 Abernathey, Ryan · 65 Beyerle, Urs · 208 Abraham, Luke · 143 Bi, Daohua · 180 Abram, Nerilie · 246 Bi, Dave · 178 Abramowitz, Gab · 181, 317 Biastoch, Arne · 53 Ackerley, Duncan · 117 Bielli, Soline · 282 Adcroft, Alistair · 83 Bindoff, Nathaniel · 15, 36, 69, 89, 328 Agusti-Panareda, Anna · 229 Bird, Michael I. · 238 Ajani, Penelope · 86 Bitz, Cecilia · 320, 321 Alberto, Polzin · 36 Black, Mitchell · 210, 211, 292 Alexander, Lisa · 174, 217, 219 Blanke, Bruno · 14 Alexander, Simon · 100 Bodhinayake, Geeth · 302 Allan, Rob · 261 Bodman, Roger · 178, 180 Allen, Kathryn · 235, 244 Boland, John · 287 Allie, Stuart · 235 Bonnardot, François · 260, 281, 282 Alves, Oscar · 196, 222 Bony, Sandrine · 114 Ambrizzi, Tércio · 202 Borges, Pablo de Amorim · 203 Ames, Kate · 335 Boschat, Ghyslaine · 147 Andreas, Prein F · 214 Boughton, Geoff · 302 Andrews, Timothy · 182 Boulter, Sarah · 346 Angélil, Oliver · 181, 207, 252 Bousquet, Olivier · 90, 282 Antoine, David · 17 Bowen, Melissa · 54, 56, 179 Aoki, Shiger · 32 Boysen, Lena · 208 Arblaster, Julie · 159, 237, 321, 323 Bozkurt, Deniz · 324 Archer, Matthew · 63 Brailsford, Gordon · 231 Armbruster, Alex · 206 Brandt, Richard · 327 Armstrong, Matthew · 234 Brassington, Gary · 37, 64 Arthur, Craig · 300, 304 Briggs, Peter · 315 Artlett, Christopher · 86 Brohan, Philip · 261 Asseng, Senthold · 343 Brovkin, Victor · 208 Ayers, Greg · 256 Brown, Andrew · 173 Brown, Jaclyn N. · 39, 343 B Brown, Josephine · 131, 347 Browning, Stuart · 259 Bruyere, Cindy · 6 Backeberg, Björn · 67 Buckley B. M. · 244 Bador, Margot · 201 Burton, Andrew · 285 Baker, Patrick · 235, 244 Busecke, Julius · 65 Ballis, Natasha · 213 Balukas, Denise · 301 Banner, Michael L. · 85 C Bannister, Tony · 104, 299 Barnes, Elizabeth A. · 139 Cahalan, Adrienne · 224 Barnston, Anthony G · 332 Cai, Shuqun · 73 Barrett, Bradford · 134 Cai, Wenju · 20, 42, 154, 159 Barthe, Christelle · 282 Callaghan, Jeffrey · 286 Barthélemy, Antoine · 21 Camp, Joanne · 284 Bauer, Nico · 226 Canadell, Pep · 225, 315 Bayr, Tobias · 157 Capet, Xavier · 35 Becker, Emily J · 332 Carey-Smith, Trevor · 210 Behera, Kumar Swadhin · 188 Carson, Greg · 235 Behrens, Erik · 19, 179

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Cavalcanti, Iracema F. A. · 169 Dare, Richard · 279 Cavicchia, Leone · 293 Dargaville, Roger · 262 Cetina-Heredia, Paulina · 64 Dätwyler, Christoph · 240 Chaffe, Pedro Luiz Borges · 203 David Sexton · 122 Chamberlain, Matt · 55, 178, 191, 193, 241 Davies, Laura · 276 Chambers, Scott · 97 Davies, Siwan M. · 238 Chand, Sarika · 336, 337 Davin, Edouard L. · 208 Chapman, Christopher · 35 Davis, Kenneth · 231 Chen, Deqiao · 126 de Lavergne, Casimir · 21, 80 Chen, Guixing · 172 de Lima Ribeiro, Andrea · 86 Chen, Hongzhuan · 128 De Maid, Robert · 93 Chen, Jingjing · 124, 127, 129 de Rességuier, Laure · 204 Chen, Shuyi · 163 Dean, Samuel · 210, 320 Chen, Xianyao · 48 Delage, François · 151 Chen, Zhiwu · 73 Deng, Difei · 277 Cheung, Kevin · 109, 283 Dennison, Fraser · 179 Chew, L.-Y. · 109 Denniston, Rhawn F. · 247 Chow, Winston T.L. · 308 Derkenne, Caro · 86 Chung, Christine C.Y. · 321 Devriendt, Laurent · 245 Church, John · 44, 48, 61, 89 Dharssi, Imtiaz · 305 Cindrić, Ksenija · 220 Di Liberto, Tom E · 332 Clarke, Hamish · 205 Di Lorenzo, Emanuele · 38, 148 Clarke, John · 345, 347 Di Luca, Alejandro · 199, 295 Clem, Kyle · 326 Di Virgilio, Giovanni · 140, 340 Cleugh, Helen · 1 Dipankar, Anurag · 311 Cleverly, James · 314 Dix, Martin · 178, 180, 185 Coleman, Thomas · 305 Dobrohotoff, Peter · 178, 180, 185 Collecutt, G. · 274 Doelman, Jonathan C. · 208 Collins, Mat · 189 Doi, Takeshi · 188 Colman, Rob · 131, 182, 347 Dolman, Bronwyn · 95 Compo, Gil · 261 Dommenget, Dietmar · 157, 160, 186 Conde Pardo, Paula · 33 Donat, Markus · 207, 217, 252 Cook, Benjamin I · 232 Donat-Magnin, Marion · 30 Cook, Edward · 232, 244 Done, James · 164, 297 Cooper, Alan · 238 Dong, Guangtao · 120, 125 Cooper, Shaun · 305 Dong, Lu · 43 Cope, Martin · 106 Dong, Shenfu · 52 Copper, Jessie Kai · 288 Dowdy, Andrew · 145, 265, 270, 293 Corrigan, Maggie E. · 105 Downes, Stephanie · 26 Cosoli, Simone · 17 Dubrovský, Martin · 168, 248 Cougnon, Eva · 31 Dunford, Mark · 304 Courtney, Joe · 285 Durack, Paul · 20 Cowtan, Kevin · 250, 254 Duran, Earl R. · 15 Crow, Brian R. · 139 Durand, Gaël · 30 Crozier, Adele · 279 Csutoros, Danny · 299 Curran, Mark · 238, 243 E Cyril, Dutheil · 201 Eamus, Derek · 314 Earl, Nick · 280 D Ebert, Elizabeth · 104, 106, 304 Edwards, Christopher A. · 78 D’Abreton, Peter · 318 Edwards, Mark · 303, 304 D’Adamo, Nick · 17 Eidt, Renata T. · 169 D’Alessandro, Adrian · 211 Ellis, Bethany · 246 da Rocha, Rosmeri · 202 Emmerson, Kathryn · 106 Dai, Zejun · 124 Engel, Chermelle B. · 276 Danian, Liu · 76

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England, Matthew · 2, 20, 25, 28, 45, 82, 150, 156, 184, Goldie, James · 219 189, 236, 241, 329 Golledge, Nicholas · 238, 242 Etheridge, David · 229, 238 Goodwin, Ian · 60, 259 Evans, Jason · 198, 199, 205, 291, 295, 317, 347 Goosse, Hughes · 21 Evans, Rob · 235, 244 Gottschalck, Jon · 332 Evenhuis, Chris · 39 Graham, Bruce · 104 Grainger, Simon · 152 Grant, David · 286 F Grant, Ian · 292 Graversen, Rune · 147 Faddy-Vrouwe, Robert · 245 Grcic, Badema · 75 Falck, Debbie · 302 Greenslade, Jesse W. · 102 Falk, Ulrike · 29 Gregory, Jonathan · 182 Fang, Wendong · 73 Gregory, Paul · 284 Feng, Ming · 12, 17, 18, 49, 69, 73 Griffin, David · 74 Fernandez, Denise · 54, 56 Griffiths, Alan · 97 Fernon, Joan · 305 Griffiths, Deryn · 307 Fest, Benedikt · 230 Griffiths, W. Ross · 84 Fichefet, Thierry · 21 Grima, Nicolas · 14 Fiddes, Sonya · 101 Groeskamp, Sjoerd · 65, 88 Fiedler, Russell · 82, 178 Grose, Michael · 182, 347 Fink, David · 245 Grosjean, Martin · 240 Fischer, Jonathan · 306 Gross, Mia · 217 Fischer, Matthew · 245 Guerette, Elise-Andrée · 102 Fisher, Jenny A. · 102 Guillod, Benoit P. · 208 Fitzpatrick, Mel · 327 Gurney, Kevin · 231 Fogwill, Christopher J. · 238 Güttler, Ivan · 220 Foley, Michael · 307 Foltz, Greg · 170 Foster, G · 250 H Fournier, Severine · 162 Frame, Dave · 210 Haberle, Simon · 104 Frankcombe, Leela · 184 Hague, Ben · 258 Franklin, Charmaine · 305 Haiyan, Zhang · 123 Fraser, Alex · 31 Halpert ,Michael S · 332 Fraser, James · 305 Ham, Yoo-Geun · 154 Frederiksen, Carsten · 152 Hamilton, Murray · 91 Frederiksen, Jorgen · 137, 185 Hannah, David · 275 Freund, Mandy · 158 Hannah, Nicholas · 82 Fu, Chenghao · 128 Hanslow, David · 296 Furue, Ryo · 15 Hardtke, Leonardo · 314 Harig, Christopher · 48 Harley, Mitchell · 296 G Harrison, A.W. · 103 Hart, Melissa · 140, 310, 339, 340, 341 Gagan, Michael · 245 Hartigan, Joshua · 271 Galbally, Ian · 99 Harvey, Mike · 141 Gallant, Ailie · 159, 237, 313 Hassim, Muhammad · 116 Galton-Fenzi, Ben · 27, 28, 31, 329 Hassol, Susan · 333 Gamble, Felicity · 332 Hattermann, Tore · 28 Garreaud, René · 215, 233, 324 Hauck, Judith · 33 Gayen, Bishakhdatta · 23, 66, 84, 330 Haumann, Alexander · 325 Ge, Ming · 297 Hausfather, Zeke · 254 Gibb, Kerry · 345 Haustein, Karsten · 209, 254 Gibson, Angus · 83 Haverd, Vanessa · 315 Ginger, John · 302, 303 Hay, Nick · 331 Glowacki, Tomasz · 305 He, Weiwei · 126 Goes, Marlos · 52, 170 He, Yinghui · 73

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Heerdegen, Aidan · 82 Iudicone, Daniele · 88 Heil, Petra · 82, 327 Heimburger, Alexie · 231 Hellmer, Hartmut · 28, 329 J Hemer, Mark · 40 Henderson, David · 302, 303 Jack, Harry · 307 Henderson, Gina · 134 Jacobs, Stephanie · 313 Hendon, Harry · 10, 49, 153, 155, 196, 212, 222, 284, Jager, Elisa · 249 323 Jakob, Christian · 108, 111, 112, 117 Heng, Su Li · 308 Jakob, Doerte · 292 Henley, Benjamin J. · 158, 213 Jan, Harlaß · 53 Hennessy, Kevin · 345 Janekovic, Ivica · 58, 75 Herger, Nadja · 181 Jerosch, Kerstin · 29 Hermes, Juliet · 67 Ji, Duoying · 226 Herold, Nicholas · 174 Ji, Fei · 199 Heron, Scott F. · 39 Jiang, Ningbo · 140 Hess, Marco · 91 Jiang, Zhu · 76 Hetzel, Yasha · 58, 75 Joh, Youngji · 148 Hewson, Michael · 335 Johnson, Fiona · 216 Hirsch, Annette · 208 Jokimaki, A · 250 Hobbs, Will · 32, 328 Jones, Chris D. · 226 Hobeichi, Sanaa · 317 Jones, Emlyn · 74 Hodgson, Dominic A · 240 Jones, Richard T. · 238 Hoeke, Ron · 40, 258 Jordan, Meredith J. T. · 103, 105 Hoffmann, David · 237 Josephine Brown · 262 Hogg, Andrew · 23, 25, 66, 82, 83 Joshi, Bibek · 288 Holbrook, Neil · 55 Jourdain, Nicolas · 30, 164, 201 Holland, Greg · 6, 164, 214, 297 Jourdain, Sylvie · 260 Holmes, Ryan M. · 150 Jullien, Swen · 201 Holper, Paul · 333, 334 Jungandreas, Leonore · 112 Hope, Pandora · 212, 265 Hopuare, Marania · 290 Horvat, Christopher · 320 K Hosen, Imran · 309 Howard, Emma · 138 Kable, Scott H. · 103, 105 Hu, Aixue · 192 Kajtar, Jules · 184, 189 Hu, Yongxiang · 107 Kala, Jatin · 309 Huang, Bohua · 167 Karion, Anna · 231 Huang, Boyin · 332 Karoly, David J. · 158, 178, 211, 213 Huang, David Defeng · 94 Katsumata, Katsuro · 34 Huang, Hans · 311 Katurji, Marwan · 204 Huck, Thierry · 14 Katzfey, Jack · 197 Hudson, Debra · 222 Kay, Merlinde · 288, 289, 291 Huete, Alfredo · 312, 314 Keating, Shane · 63, 64, 80 Hughes, Terry · 5 Keay, Kevin · 263, 344 Humphreys, Mitch · 302 Keller, David P. · 226 Huneke, Wilma · 27 Keller, Elizabeth · 231 Hunter, Jasmine · 245 Kelly-Gerreyn, Boris · 93 Hunter, John · 31 Kendrick, Gary · 17 Huth, Radan · 168, 248 Kennedy, Ivan · 142 Hyun-Su, Jo · 50 Kepert, Jeff · 304 Kerns, Brandon · 163 Kerry, Colette · 72, 77, 78 I Kestenare, Elodie · 22 Kettlewell, Graham · 102 Ioanna, Ioannou · 307 Kharazmi, A. · 103 Irving, Damien · 89 Kiem, Anthony · 234, 243 Islam, AKM Saiful · 209 Kim, Hyungjun J. · 208

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Kim, Sung Yong · 62 Leng, Song · 314 King, Andrew · 211, 213 Lengaigne, Matthieu · 201 King, Matt · 47, 48 Lenton, Andrew · 33, 39, 226, 227 King, Philip · 298 Levine, Richard · 119 Kingston, Daniel · 275 Lewandowsky, S · 250 Kinsela, Michael · 296 Lewis, Sophie · 219, 333 Kinter, James · 167 Li, Jianping · 121 Kirtman, Ben · 170 Li, Weibiao · 172 Kiss, Andrew · 82, 83 Li, Yanjie · 121 Kitsios, Vassili · 185, 195 Li, Ying · 114 Klingamann, Nicholas P. · 118 Li, Yue · 164 Klocker, Andreas · 27, 33 Li, Zhihong · 305 Kloetzke, Thomas · 302 Liang, Ping · 120, 125 Knutti, Reto · 181 Liguori, Giovanni · 148 Koh, T.-Y. · 109 Lim, Eun-Pa · 155, 212 Kohno, Mika · 238 Lin, Po-Hsiung · 166 Krause, Claire · 300, 304 Lipson, Mathew · 310 Kravitz, Ben · 226 Lisonbee, Joel · 115 Krummel, Paul · 229 Liu, Junliang · 73 Krupar III, Richard · 273, 302 Liu, Qin-Yan · 12 Krysta, Monika · 305 Loh, Zoë · 229 Kuchinke, Mareva · 39 Looker, Clare · 299 Kug, Jong-Seong · 154 Lorrey, Andrew · 261 Kuleshov, Yuriy · 174, 284 Louis, Simon · 294 Kumar, Ravind · 177 Loveday, Nicholas · 307 Lu, Wenming · 305 Lucas, Chris · 145, 279 L Lucas-Svay, Lorene · 290 Luhar, Ashok · 99 L’Heureux, Michelle · 332 Lumpkin, Rick · 63 Lafleur, Dimitri · 230 Luo, Jing-Jia · 153, 196 Lam, Sean · 318 Lupton, John · 26 Lamichhane, Bishnu · 271 Lynch, Amanda · 267 Lan, Ruoyu · 172 Landesman, Paul · 87 Lane, Agnes · 93 M Lane, Todd · 101, 161, 165, 276 Langhorne, Pat · 179 Ma, Yimin · 305 Langlais, Clothilde · 33, 39 Macadam, Ian · 199 Laohalertchai, Charoon · 167 Mackensen, Andreas · 29 Latif, Mojib · 157, 322 MacLachlan, Craig · 284 Laubach, Johannes · 316 Madec, Gurvan · 30, 80 Laurent, Victoire · 176 Maes, Christophe · 14 Lauvaux, Thomas · 231 Magee, Andrew · 175 Lavers, David · 275 Magill, Christina · 283 Law, Rachel · 178, 227, 229, 262 Maharaj, Angela M. · 340 Le Roux, Renan · 204 Maher, Nicola · 4, 183 Le Sommer, Julien · 30 Majumder, Sudip · 52 Lecacheux, Sophie · 282 Malan, Neil · 67 Lecomte, Olivier · 21 Manickam, Mey · 279 Lee, Eun Ae · 62 Mann, Michael · 184 Lee, Jin · 305 Mantua, Nathan · 38 Lee, Tong · 162 Maoyuan, Liu · 307 Lefevre, Jérôme · 201 Mapes, Brian · 110 Legras, B. · 109 Maria, Carvalho · 122 Legrésy, Benoit · 31, 48 Marin, Julio · 324 Lehmann, Karsten · 181 Marinović, Ivana · 220 Leitch, Anne · 346 Markham, J. · 54

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Marotzke, Jochem · 183 Morrow, Rosemary · 22, 68 Marshall, Andrew · 18, 284 Mosquera-Vasquez, Kobi · 332 Marshall, Gareth · 143 Moy, Andrew · 238, 243 Marsland, Simon · 178, 180 Mullan, Brett · 200 Martin, Gill M. · 118, 119, 122 Mullendore, Gretchen · 113 Martinez, Elodie · 14 Munksgaard, Niels C. · 238 Mason, Matthew · 270, 273, 302 Munroe, James · 82 Masumoto, Yukio · 11 Muri, Helene · 226 Matear, Richard · 193, 241 Murphy, Brad · 292 Matei, Daniela · 183 Muthukumaran, S. · 309 Mathiot, Pierre · 30 Matthews, Naveen · 228 Mayo, Richard · 91 N Mazzatenta, Claudio · 338 McAlpine, Clive · 132 Nagura, Motoki · 11 McCauley, Robert · 17 Narsey, Sugata · 117 McDonald, Adrian · 141, 179 Nathan, Rory J. · 213 McDougall, Trevor · 80 Naughten, Kaitlin · 28, 329 McGowan, Hamish · 270 Naughton, Michael · 305 McGree, Simon · 174 Naveira Garabato · 36 McGregor, Helen · 245 Neske, Sonja · 149 McGregor, James · 326 Neukom, Raphael · 240 McGregor, John · 197 Newbigin, Edward · 104, 106 McGregor, Shayne · 13, 149, 156, 189 Ng, A.W.M. · 309 McInnes, Kathleen · 40, 61, 258 Nguyen, Hanh · 145, 153, 173 McIntosh, Peter C. · 343 Nicholls, Neville · 159 McKay, Nicholas P. · 238 Nikoobahkt, Behnam · 105 McNaughton, Keith · 316 Nistor, Benjamin · 146 McPhaden, Michael · 43 Nitta, Tomoko · 208 Meehl, Gerald A. · 192, 321 Noone, David · 262, 266 Meissner, Katrin · 28, 241, 329 Norford, L. · 109 Meister, Julien · 282 Nuynh, H.-N. · 109 Menkes, Christophe · 201 Menviel, Laurie · 241 Meredith, Michael · 29 O Merryfield, William · 190 Meyssignac, Benoit · 44 O’Farrell, Siobhan · 180 Middleton, Jason · 296 O’Grady, Julian · 40, 258 Mikaloff Fletcher, Sara · 231 O’Kane, Terence · 55, 187, 191, 193, 194, 195 Miles, Elaine · 59 O’Leary, Mick · 60 Miles, Natasha · 231 Ogata, Tomomichi · 11 Millman, Helen · 238 Oke, Peter · 74, 82 Milton, Sean · 119, 122 Oliver, Eric · 18, 55 Mitchell, Bill · 258 Olivieri, Marco · 44 Mitchell, Dann · 208 Oreskes, N · 250 Mitrovica, Jerry · 60 Orr, Andrew · 143 Mo, Ruping · 124, 127, 128, 129, 130 Ortega, Pascal · 290 Moebis, Benjamin · 111 Osbrough, Stacey · 137 Moise, Aurel F. · 118, 119, 125, 126, 127, 131, 347 Osman, Marisol · 144 Moltmann, Tim · 16 Otto, Friederike E.L. · 209, 254 Mondal, Mainak · 330 Monselesan, Didier · 48, 61, 194 Morgan, Adam · 298 P Morgan, Ruth · 257 Morgenstern, Olaf · 141, 179 Pak, Bernard · 262 Morioka, Yushi · 188 Palmer, Jonathan · 232, 242 Morison, Russel P. · 85 Palmer, Paul I. · 102 Morrison, Adele · 25 Palutikof, Jean · 346

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Pan, He · 172 Rayner, Peter · 230, 262 Parackal, Korah · 302, 303 Reason, Chris · 67 Parfitt, Rhys · 264 Reboita, Michelle · 202 Park, Wonsun · 322 Recouvreur, Romain · 282 Parker, Tess · 272 Reeder, Michael · 108, 117, 272, 276 Parsons, Simon · 141 Renguang, Wu · 123 Partridge, Julian · 17 Rennie, Susan · 305 Pasarić, Zoran · 220 Renwick, James · 146, 326 Pask, Helen · 86 Rhodes, Steve · 92 Paton-Walsh, Clare · 102 Ribbat, Nina · 70 Patra, Prabir · 228 Ribbe, Joachim · 115 Patterson, Matt · 135 Ribo, Marta · 60 Pattiaratchi, Charitha · 17, 58, 75 Rice, Martin · 331 Paviet-Salomon, Thomas · 14 Richardson, Scott · 231 Pearce, Karen · 345 Richter, Harald · 270, 274, 286, 304 Pearce, Petra · 200, 261 Richter, Kristen · 44 Peel, Murray C. · 213 Rickard, Graham · 19 Peltier, Alexandre · 173, 201, 260 Ridgway, Ken · 9, 57 Peña-Molino, Beatriz · 32 Rikus, Lawrie · 292, 305 Pepler, Acacia · 265, 295 Rimi, Ruksana H · 209 Perry, Sarah · 156 Rintoul, Stephen · 26, 31, 32, 33, 45 Peters, Karsten · 111 Risbey, James · 194, 250 Pezza, Alex · 200 Rissik, David · 346 Phillips, Helen E. · 15, 36, 69 Ritchie, Elizabeth A. · 277, 285, 301 Phipps, Steven J. · 47 Rivera, Andres · 238 Pitman, Andy · 252, 291 Roach, Lettie · 320 Pitts, Owen · 318 Roberts, Jason · 47, 243 Polito, Paulo · 51 Roberts, Stephen J · 240 Pook, Mike · 194 Robie, David · 336 Pope, James · 143 Rocha, Carlos · 78 Potts, Rod · 279 Rocheta, Eytan · 198 Powell, Brian · 77 Rodrigues, Regina · 41, 171 Power, Scott · 151, 334 Rodriguez, Jose · 122 Prasad, Abhnil · 289, 291 Roesler, Collin · 327 Prein, Andreas · 6 Rondanelli, Roberto · 324 Preunkert, Susanne · 97 Rootes, Camilla M. · 238 Price, Benjamin · 307 Rosier, Suzanne · 146, 210 Protat, Alain · 111, 270 Roth, Matthias · 311 Purich, Ariaan · 20, 147 Roughan, Moninya · 63, 64, 70, 71, 72, 77, 78 Rubino, Mauro · 238 Rudeva, Irina · 263 Q Ruiz Barlett, Eduardo · 29 Ryu, Hyeuk · 303 Queiroz, Eduardo · 72 Quénol, Hervé · 204 Quetelard, Hubert · 281 S Quinting, Julian · 272 Sakov, Pavel · 187, 191 Salazar, Alvaro · 132 R Sallée, Jean-Baptiste · 33, 35 Sanabria, Augusto · 300 Rafter, Tony · 221 Sanchez, Claudio · 122, 311 Rahmstorf, Stefan · 238, 250 Sanderson, Benjamin M. · 181 Raphael, Marilyn · 325 Sandery, Paul · 187, 191 Rashid, Harun · 178, 180 Sang-Wook, Yeh · 50 Rasuly, Ali Akbar · 283 Santoso, Agus · 46 Rathore, Saurabh · 69 Sato, Olga · 51 Raut, Bhupendra · 111 Saunders, Krystyna M · 240

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Savarin, Ajda · 163 Stehfest, Elke · 208 Schloss, Irene · 29 Steinberg, Craig · 57 Schlosser, Elisabeth · 325 Steinle, Peter · 93, 305 Schmid, Claudia · 52 Steinman, Byron · 184 Schofield, Robyn · 101 Stevens, Lauren · 193 Schreider, Sergei · 174 Stewart, Kial · 87 Schroeter, Serena · 328 Stone, Dáithí · 207 Schuddeboom, Alex · 141 Stringer, Russell · 304 Schurer, Andrew · 254 Stuecker, Malte F. · 189 Schwarzkopf, Franziska U. · 53 Sturman, Andrew · 204 Scott, Vivian · 226 Sui, Chung-Hsiung · 166 Screen, James · 253, 268 Sulaiman, Asri · 305 Sen Gupta, Alex · 39, 156, 164, 236 Sullivan, Arnold · 20, 178, 180 Seneviratne, Sonia I. · 208 Sun, Xudong · 305 Sexton, Jane · 304 Surl, Luke · 102 Sgarbossa, Dean · 278 Suthers, Iain · 70 Shakespeare, Callum · 83 Sutton, Phil · 54 Sharma, Ashish · 198 Sutton, Philip · 56 Shaw, M.F. · 103 Sweeney, Colm · 231 Shay, Lynn K. · 63 Syktus, Jozef · 132 Shears, Nick · 54 Shen, Felix Xi · 94 Shepson, Paul · 231 T Sherwood, Steven · 219 Shiogama, Hideo · 208 Taggart, Robert · 307 Short, Ewan · 165 Tailleux, Rémi · 81 Sidiqui, Paras · 312 Tait, Andrew · 200 Sikand, Monika · 338 Takacs, George · 249 Silva Busso, Adrián · 29 Takahashi, Ken · 332 Silvano, Alessandro · 32 Talley, Lynne · 24 Silver, Jeremy · 104, 106 Tamsitt, Veronica · 24 Sime, Louise · 240 Tamura, Takeshi · 32 Simmonds, Ian · 147, 263, 280, 319 Tang, Xiaowen · 94 Simón-Moral, Andrés · 311 Tapper, Nigel · 313 Sims, Holly · 104 Tardy, Marc · 260 Singh, Martin · 112, 136 Taschetto, Andréa S. · 41, 51, 164, 236 Siqueira, Leo · 170 Tebaldi, Claudia · 7, 206 Slangen, Aimée · 44 Teng, Haiyan · 192, 321 Sloyan, Bernadette · 26 Teo, C.-K. · 109 Smith, Ben · 315 Thatcher, Marcus · 132, 197, 310, 315 Smith, Daniel · 302, 303 Thomas, Zoë · 238, 242 Smith, Inga · 179 Thompson, David W. J. · 114, 139 Smith, Madison · 320 Thompson, Jeremy · 231 Socha, Aaron · 338 Thorn, Dominic · 319 Soderholm, Joshua · 270, 271, 286 Thornton, David P. · 238 Sohail, Taimoor · 23 Timbal, Bertrand · 116 Soldatenko, Sergei · 93 Timmermann, Ralph · 28, 329 Song, Siwon · 110 Tingwell, Chris · 93 Spada, Giorgio · 44 Toivanen, Jussi · 276 Sparrow, Sarah · 208, 210 Tonmoy, Fahim · 346 Spassiani, Alessio · 273 Torok, Simon · 333, 334 Speirs, Johanna · 341 Tory, Kevin · 284 Spence, Paul · 13, 15, 25, 30, 82, 241 Tozer, Carly · 194, 243 Splinter, Kristen · 296 Tran, Nguyen Ngoc · 314 Sproul, Alistair Bruce · 288 Treloar, A. · 274 Stark, Clair · 285 Trenham, Claire · 258 Stassen, Christian · 186 Trewin, Blair · 218, 251 Stavert, Ann · 229 Trudinger, Cathy · 315

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Tully, Matt · 92, 98 Weir, Tony · 177 Turnbull, Jocelyn · 231 Wengel, Christian · 157 Turner, Ian · 296 Wenju, Cai · 50 Turner, Kathryn · 286 Wheeler, Matthew · 284 Turney, Chris · 238, 242 Whitaker, Richard · 342 Tyo, J. Scott · 285 White, Bethan · 108 White, Duanne A. · 47 Wiedinmyer, Christine · 96 U Wijffels, Susan · 12, 49, 89 Wilkinson, Clive · 261 Uhe, Peter F · 209 Williams, Alastair · 97 Ukkola, Anna · 317 Williams, Guy · 31, 32 Ummenhofer, Caroline C. · 236, 247, 264 Williams, Jonny · 179 Williams, Mike · 179 Williams, Scott · 298 V Williams, Ted · 299 Wilson, Simon · 208 Valenzuela, Raul · 215 Winter, Kate · 238 van Leeuwen, Cornelis · 204 Wittenberg, Andrew T · 332 van Ommen, Tas · 238 Wong, Henri · 245 van Rensch, Peter · 159 Wong, Keith · 338 van Sebille, Erik · 64, 238 Wood, Kim M. · 301 van Vuuren, Detlef P. · 208 Woodhouse, Matthew · 99, 101 van Wijk, Esmee · 32 Woodroffe, Colin · 245 Vance, Tessa · 243 Woodward, John · 238 Varma, Vidya · 179 Woollings, Tim · 135, 171 Vaughan, Naomi E. · 226 Wotherspoon, Simon · 55 Venema, Victor · 254 Wu, Quran · 54 Vera, Carolina · 144 Wu, Xianyun · 129 Verdon-Kidd, Danielle · 175 Vialard Jérôme · 201 Viale, Maximiliano · 215 X Vijayeta, Asha · 160 Vincent, Claire · 161, 165, 173 Xiao, Yi · 305 Vreugdenhil, Catherine · 84 Xiao, Ziyu · 79 Xie, Jieshuo · 73 Xu, Jiexin · 73 W Xu, Kuanman · 107 Xu, Lin · 128, 129, 130 Wain, Alan · 106, 279 Xu, Ying · 125 Wales, Scott · 276 Walland, David · 292 Walsh, Kevin · 293 Y Wang, Dongxiao · 12 Wang, Enli · 343 Yan, Hailin · 180 Wang, Guomin · 212, 323 Yang, Song · 167 Wang, Xiao Hua · 79 Yang, Woo-Hyun · 154 Wang, Yuqing · 297 Ye, Chengzhi · 120, 124, 125, 126, 127, 129, 130 Warren, Robert · 271 Yeqiang, Shu · 76 Warren, Stephen · 327 Ying, Xu · 133 Waterman, Stephanie · 36 Yoo, Jang Gon · 62 Watkins, Andrew · 269, 284, 332, 344 Yu, J. · 241 Watson, Christopher S. · 48 Yuehua, Li · 80 Way, Robert G. · 254 Webb, Steve · 346 Webster, Stuart · 276 Z Wedd, Tony · 270, 286 Wehner, Martin · 303, 304 Zawar-Reza, Peyman · 204

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Zeller, Mathias · 13 Zhiping, Wen · 123 Zeng, Wenxin · 172 Zhou, Jian-xin · 245 Zhang, Huqiang · 120, 125, 126, 127 Zhu, Hongyan · 305 Zhang, Jianqi · 124 Zickfeld, Kirsten · 226 Zhang, Tuantuan · 167 Zidikheri, Meelis · 279 Zhang, Xuebin · 48, 54, 61 Ziehn, Tilo · 178, 227 Zhao, Mei · 120 Zika, Jan D. · 150 Zhao, Sen · 121 Zsom, Andras · 267 Zhao, Yingying · 148 Zunz, Violette · 21

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