DOCSLIB.ORG

Introduction to Tropical Meteorology and Deep Convection

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Introduction to Tropical Meteorology and Deep Convection Introduction to tropical meteorology and deep convection Roger K. Smith University of Munich Thai Meteorological Department Lecture 1 Topics A satpix tour of the tropics The zonal mean circu lati on (H adl ey ci rcul ati on) , I nt er- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, westerly wind burst INDO IR 01010510 GMS IR 01022621 GOES IR 00112909 EUMETSAT Movie A numerical simulation Principal land and ocean areas between 40°S and 40°N. The shaded areas show tropical highlands (over 1000 m). From Nieuwolt (1977) How does one define the tropics? Tropic of Cancer 23.5oN MitiMaritime continent Tropic of Capricorn 23.5os Next topic A satpix tour of the tropics The zonal mean circu lati on (H adl ey ci rcul ati on) , I nt er- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, westerly wind bursts energy gain 300 + energy loss )) 2 200 W m Radiative heat balance (( Absorbed solar flux F 100 Emitted infrared flux 0 90 50 30 10 0 10 30 50 90 South Latitude North Zonally averaged components of the absorbed solar flux and emitted thermal infrared flux at the top of the atmosphere. (after Vonder Haar and Suomi, 1971, with modifications) 2000 1500 mm 1000 Mean annual precipitation 500 0 90 60 40 30 20 10 0 10 20 30 40 60 90 North Latitude South Mean annual precipitation as a function of latitude. (after Sellers, 1965) mean meridional ci rcul ati on The mean meridional circulation and main surface wind regimes . after Defant, 1958 ITCZ ITCZ Next topic A satpix tour of the tropics The zonal mean circulation (Hadley circulation), Inter- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, westerly wind bursts Field Exppperiments in the Tropics Global Atmospheric Research Programme ( GARP) Atlantic Tropical Experiment (GATE) July 1974 The MONsoon EXpp(eriment (WMONEX December 1978 , SMONEX May – August, 1979) Australian Monsoon EXperiment & Equatorial Mesoscale EXperiment (AMEX, EMEX) January – February 1987 Tropical Oceans Global Atmosphere Couple Ocean Atmosphere Response Experiment (TOGA COARE) November 1992 – February 1993 Next topic A satpix tour of the tropics The zonal mean circu lati on (H adl ey ci rcul ati on) , I nt er- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, westerly wind bursts 200 mb JJA 850 mb 200 mb DJF 850 mb Velocity potential We can separate the three-dimensional velocity field into a rotational part and a divergent part (see e .g . Holton, 1972, Appendix C.) Vk rottitationa l ittilirrotational nondivergent divergent ()kk 2 ()0 ()0k () 2 Upper tropospheric (200 mb) mean seasonal velocity potential indicating the divergent part of the mean seasonal wind which is proportional to . (Adapted from Krishnamurti et al., 1973). month OLR < 225 W m2 From Lau & Chan, 1983 Walker circulation Next topic A satpix tour of the tropics The zonal mean circu lati on (H adl ey ci rcul ati on) , I nt er- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, westerly wind bursts Monsoons July SE Asian Monsoon January Australasian Monsoon South America: January climatology 850 mb wind 200 mb wind An example of monsoon variability West coast 1963 of India 1971 (From Webster, 1983) Next topic A satpix tour of the tropics The zona l mean c ircu ltilation (H (Hdladley ci rcul lti)Itation), Inter- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, Westerly wind bursts Time-longitude section of vis imagery - latitude band 10 -15 N 01/06 0107 0108 e tim From Wallace, 1970 Winter MONEX A B GMS – IR 25 Dec 1978 C Fig. 1.23 MSLP 25 Dec 1978 From Webster, 1983 Winter MONEX A 250 mb 25 Dec 1978 B C Fig. 1.24 shaded horizontal wind divergence A 850 mb 25 Dec 1978 C B From Webster, 1983 The variation of surface pressure at Darwin for the period 23 - 28 Dec. 1978. Easterly waves over Africa WV Imagery 17 June 1997 00Z Tropical cyclones Super typhoon Wynnie 11 Aug 1997 TC tracks (1979-1988) Next topic A satpix tour of the tropics The zonal mean circu lati on (H adl ey ci rcul ati on) , I nt er- Tropical Convergence Zone (ITCZ) Field experiments Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves Moist convection and convective systems The Madden-Julian Oscillation, westerly wind bursts Concluding remarks Moist Convection Trade Cumuli The tropical troposphere z km 15 -121oC -73oC obdbserved -150oC +150oC 29oC 77oC observed Conclusion: Deep tropical circulations cannot be dry adiabatic The role of diabatic processes z km 15 Latent heat Radiative cooling opposes adiabatic release Fast warming opposes ascent adiabatic Slow descent cooling ITCZ subtropical high Conclusion: Deep convection occupies a small fractional area Radar reflectivityy() contours (dBZ) of SiltifdSuccessive locations of radar a tropical squall line observed during reflectivity contours in a tropical COPT81 (Ivory Coast, West Africa). squall line. Horizontal cross-section at low levels From Chang et al. (1987) (0.5 – 1.5 km). Radar reflectivityy()pq contours (dBZ) of a tropical squall line observed during COPT81 (Ivory Coast, West Africa). Vertical cross-section along the axis of propagation. Types of convection “Hector”, Darwin, Australia Next topic A satpix tour of the tropics The zonal mean circulation (Hadley circulation) , Inter - Tropical Convergence Zone (ITCZ) Field experi ment s Macroscale circulations, The Walker circulation, Monsoons Synoptic scale weather systems, tropical waves MitMoist convecti on and convecti ve syst ems The Madden-Julian Oscillation, westerly wind bursts Madden-Julian Oscillation From JAS, Sept. 1972 Madden-Julian Oscillation MJO From Webster 1987 Indian Ocean Feb/Mar 2001 06/02 07/02 13/02 17/02 24/02 06/03 West Pacific Ocean – Feb 2001 06/02 09/02 13/02 21/02 24/02 29/02 http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/hov.last6mths.anom.S.gif Westerly wind bursts GOES-9 12 UTC 2 Dec 1997 10.7 micron image Solution for and Y The extended Held-Hou Model M0 u = UM z YY y unknowns Pole Winter Summer Eq. u = 0 Y y Cellcell Cellcell 2 1/2 0 42 5gH M022YY E0 Y 10a gH 3a 2 30 2 0 42 2 M022YY E0 5gH 2a gH a M0 E0 22 Y- Eq. Y0 Y1 Y+ 18a 0 Take 0 = 255 K, = 40 K and H = 12 km Y 2400 km and Streamline dividing the 0.9 K cooler than . Solar heating maximum winter and summer cells in agreement with obs. Kelvin wave dv 2 2 uY v dY Scale and put y = L Y E dv 22 Yv dY Mixed R-GGw wave Parcel 1 2 Now vY () v nnexp 2 Y H ( Y ) motions dv dH and Yv exp 1 Y2 n dY n 2 dY dHn Properties of the 2nHn1 () Y Hermite polynomials dY HY()22 YHYnHY () () nnn11Horizontal structure of the Kelvin wave and of a westward propagating Mixed Rossby-gravity wave. A few outstanding problems Interaction between moist convection and the large-scale flow. What are the controls on deep convection? Models usually don’t get the diurnal variation correct. No generally accepted theory of the Madden-Julian Oscillation. Weather forecasting in the tropics is still very difficult compared with that in the middle latitudes! The End.
Load more

Recommended publications
  • Link Between the Double-Intertropical Convergence Zone Problem and Cloud Biases Over the Southern Ocean
    Link between the double-Intertropical Convergence Zone problem and cloud biases over the Southern Ocean Yen-Ting Hwang1 and Dargan M. W. Frierson Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195-1640 Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved February 15, 2013 (received for review August 2, 2012) The double-Intertropical Convergence Zone (ITCZ) problem, in which climate models show that the bias can be reduced by changing excessive precipitation is produced in the Southern Hemisphere aspects of the convection scheme (e.g., refs. 7–9) or changing the tropics, which resembles a Southern Hemisphere counterpart to the surface wind stress formulation (e.g., ref. 10). Given the complex strong Northern Hemisphere ITCZ, is perhaps the most significant feedback processes in the tropics, it is challenging to understand and most persistent bias of global climate models. In this study, we the mechanisms by which the sensitivity experiments listed above look to the extratropics for possible causes of the double-ITCZ improve tropical precipitation. problem by performing a global energetic analysis with historical Recent work in general circulation theory has suggested that simulations from a suite of global climate models and comparing one should not only look within the tropics for features that affect with satellite observations of the Earth’s energy budget. Our results tropical precipitation. A set of idealized experiments showed that show that models with more energy flux into the Southern heating a global climate model exclusively in the extratropics can Hemisphere atmosphere (at the top of the atmosphere and at the lead to tropical rainfall shifts from one side of the tropics to the surface) tend to have a stronger double-ITCZ bias, consistent with other (11).
    [Show full text]
  • Tropical Weather Discussion
    TROPICAL WEATHER DISCUSSION • Purpose The Tropical Weather Discussion describes major synoptic weather features and significant areas of disturbed weather in the tropics. The product is intended to provide current weather information for those who need to know the current state of the atmosphere and expected trends to assist them in their decision making. The product gives significant weather features, areas of disturbed weather, expected trends, the meteorological reasoning behind the forecast, model performance, and in some cases a degree of confidence. • Content The Tropical Weather Discussion is a narrative explaining the current weather conditions across the tropics and the expected short-term changes. The product is divided into four different sections as outline below: 1. SPECIAL FEATURES (event-driven) The special features section includes descriptions of hurricanes, tropical storms, tropical depressions, subtropical cyclones, and any other feature of significance that may develop into a tropical or subtropical cyclone. For active tropical cyclones, this section provides the latest advisory data on the system. Associated middle and upper level interactions as well as significant clouds and convection are discussed with each system. This section is omitted if none of these features is present. 2. TROPICAL WAVES (event-driven) This section provides a description of the strength, position, and movement of all tropical waves analyzed on the surface analysis, from east to west. A brief reason for a wave’s position is usually given, citing surface observations, upper air time sections, satellite imagery, etc. The associated convection is discussed with each tropical wave as well as any potential impacts to landmasses or marine interests.
    [Show full text]
  • ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
    ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere.
    [Show full text]
  • ESCI 344 – Tropical Meteorology Lesson 3 – General Circulation of the Tropics
    ESCI 344 – Tropical Meteorology Lesson 3 – General Circulation of the Tropics References: Forecaster’s Guide to Tropical Meteorology (updated), Ramage Climate Dynamics of the Tropics, Hastenrath Tropical Climatology (2nd ed), McGregor and Nieuwolt Tropical Meteorology, Tarakanov Climate and Weather in the Tropics, Riehl General Circulation of the Tropical Atmosphere, Vol II, Newell et al. “The South Pacific Convergence Zone (SPCZ): A Review”, Vincent, Mon.Wea. Rev., 122, 1949-1970, 1994 “The Central Pacific Near-Equatorial Convergence Zone”, Ramage, J. Geophys. Res., 86, 6580-6598 Reading: Introduction to the Meteorology and Climate of the Tropics, Chapter 3 Vincent, “The SPCZ: A Review” Lau and Yang, “Walker Circulation” James, “Hadley Circulation” Waliser, “Intertropical Convergence Zones” Hastenrath, “Tropical Climates” Madden, “Intraseasonal Oscillation (MJO)” TERMINOLOGY Boreal refers to the Northern Hemisphere Austral refers to the Southern Hemisphere LATITUDINAL HEAT IMBALANCE Net radiation flux is defined as the difference in incoming radiation flux and outgoing radiation flux. A positive net radiation flux indicates a surplus of energy, while a negative net radiation flux indicates a deficit. This figure shows the longitudinally-averaged, annual-mean radiation fluxes at the top of the atmosphere. Outgoing shortwave is due to scattering and reflection. Net shortwave is the difference between the incoming and outgoing shortwave radiation. When the earth-atmosphere system is considered as a whole, there is a positive net radiation flux between about 40N and 40S, while there is a negative net radiation flux poleward of 40 in both hemispheres. In order for a steady-state temperature to be achieved, there must be transport of heat from the earth’s surface to the atmosphere, and from the tropics to the polar regions.
    [Show full text]
  • Synoptic Meteorology
    Lecture Notes on Synoptic Meteorology For Integrated Meteorological Training Course By Dr. Prakash Khare Scientist E India Meteorological Department Meteorological Training Institute Pashan,Pune-8 186 IMTC SYLLABUS OF SYNOPTIC METEOROLOGY (FOR DIRECT RECRUITED S.A’S OF IMD) Theory (25 Periods) ❖ Scales of weather systems; Network of Observatories; Surface, upper air; special observations (satellite, radar, aircraft etc.); analysis of fields of meteorological elements on synoptic charts; Vertical time / cross sections and their analysis. ❖ Wind and pressure analysis: Isobars on level surface and contours on constant pressure surface. Isotherms, thickness field; examples of geostrophic, gradient and thermal winds: slope of pressure system, streamline and Isotachs analysis. ❖ Western disturbance and its structure and associated weather, Waves in mid-latitude westerlies. ❖ Thunderstorm and severe local storm, synoptic conditions favourable for thunderstorm, concepts of triggering mechanism, conditional instability; Norwesters, dust storm, hail storm. Squall, tornado, microburst/cloudburst, landslide. ❖ Indian summer monsoon; S.W. Monsoon onset: semi permanent systems, Active and break monsoon, Monsoon depressions: MTC; Offshore troughs/vortices. Influence of extra tropical troughs and typhoons in northwest Pacific; withdrawal of S.W. Monsoon, Northeast monsoon, ❖ Tropical Cyclone: Life cycle, vertical and horizontal structure of TC, Its movement and intensification. Weather associated with TC. Easterly wave and its structure and associated weather. ❖ Jet Streams – WMO definition of Jet stream, different jet streams around the globe, Jet streams and weather ❖ Meso-scale meteorology, sea and land breezes, mountain/valley winds, mountain wave. ❖ Short range weather forecasting (Elementary ideas only); persistence, climatology and steering methods, movement and development of synoptic scale systems; Analogue techniques- prediction of individual weather elements, visibility, surface and upper level winds, convective phenomena.
    [Show full text]
  • BASIC WEATHER CONCEPTS CHAPTER TWO WIND, PRESSURE • Be Familiar with Global Wind Patterns
    LLI BASIC WEATHER CONCEPTS CHAPTER TWO WIND, PRESSURE • Be familiar with global wind patterns. • Understand barometric pressure. • Know the factors that affect the wind. • Predict the circulation of winds around highs and lows. • Determine the direction to a low. • Understand winds aloft and how they differ from surface winds. 1 EquatorPole Air Flow warm equatorial air rises, then moves to cooler mid-latitude regions then sinks 2 Mid-latitude High note each higher latitude region is colder until Pole is reached 3 What is a Hadley Cell? The Hadley cell, named after George Hadley, is a global scale tropical atmospheric circulation that features air rising near the equator, flowing poleward at 10–15 kilometers above the surface, descending in the subtropics, and then returning equatorward near the surface. This process maintains the Global Energy Balance preventing the equator from becoming hotter and polar regions becoming colder. 4 Global Highs and Lows 5 Global Winds 6 Video of Atmospheric Circulation • Global Atmospheric Circulation 1:54 mins. • https://www.youtube.com/watch?v=DHrapzH PCSA 7 European Explorers used Tradewinds St. Augustine >30˚ N > 30˚ S 9 Land Masses Modify Global Pattern 10 Key Points to Remember about Heat and Pressure • Heat: energy (heat) is always transferred from WARM to COLD • Pressure: pressure always flows from HIGH to LOW 11 Pressure Differences – HIGH pressure areas – like Hills – LOW pressure areas – like valleys Earth’s rotation causes winds to turn rather than travel straight from high to low 12 Winds around Highs and Lows highs-clockwise, lows counterclockwise 13 Movement of Air in Low Pressure and High Pressure Regions • Air molecules* move counterclockwise (in the Northern Hemisphere) and rise in a low pressure area.
    [Show full text]
  • The Intertropical Convergence Zone of the Eastern Pacific Region (I)*
    The Intertropical Convergence Zone of the Eastern Pacific Region (I)* MAJOR LEO ALPERT, A.C. Hq. AAF Weather Service, Asheville, N. C. INTRODUCTION Recently a large number of weather ob- servations have become available from air- ITTLE INFORMATION concerning the craft patrols in the Eastern Pacific Ocean structure and position of the inter- L between 90°W to 95°W Longitude, and 7°S tropical convergence zone in the East- to 14°N Latitude. From December 1941 to ern Pacific Ocean was available prior to the late 1944, hourly weather observations were war. As daily weather reports from ships made daily by patrol aircraft, flying between have never been numerous from this area, the Republic of Guatemala in Central Amer- all attempts to show the position of the ica, the Galapagos Archipelago and the main- intertropical convergence zone based upon land of Ecuador in South America. Data an interpretation of summarized ship re- for the period February 1942 to January ports are open to question. The charts pub- 1944 have been plotted on daily charts and lished in the " Atlas of Climatic Charts of analyzed by the author. the Oceans'n are probably the best of these The grand total of observations available for this region. They are based upon fre- from the aircraft patrols in the area from quencies of true-wind directions determined 10°N to 5°S for the period February 1942 by observing the effect of wind on the sea to January 1944, inclusive, is two to four surface from a moving ship at Greenwich times as great as the grand total of observa- Noon during the period 1885-1933.
    [Show full text]
  • Two Phases of the Holocene East African Humid Period: Inferred From
    Earth and Planetary Science Letters 460 (2017) 123–134 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Two phases of the Holocene East African Humid Period: Inferred from a high-resolution geochemical record off Tanzania ∗ Xiting Liu a,b, , Rebecca Rendle-Bühring b, Holger Kuhlmann b, Anchun Li a a Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China b MARUM – Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen, D-28359 Bremen, Germany a r t i c l e i n f o a b s t r a c t Article history: During the Holocene, the most notably climatic change across the African continent is the African Received 10 August 2016 Humid Period (AHP), however the pace and primary forcing for this pluvial condition is still ambiguous, Received in revised form 2 December 2016 particularly in East Africa. We present a high-resolution marine sediment record off Tanzania to provide Accepted 11 December 2016 insights into the climatic conditions of inland East Africa during the Holocene. Major element ratios Available online xxxx (i.e., log-ratios of Fe/Ca and Ti/Ca), derived from X-Ray Fluorescence scanning, have been employed to Editor: M. Frank document variations in humidity in East Africa. Our results show that the AHP is represented by two Keywords: humid phases: an intense humid period from the beginning of the Holocene to 8ka (AHP I); and a African Humid Period moderate humid period spanning from 8 to 5.5 ka (AHP II).
    [Show full text]
  • How Does Intertropical Convergence Zone Variation Impact on Tropical Cyclone in the Northern Hemisphere?
    Geophysical Research Abstracts Vol. 19, EGU2017-16196, 2017 EGU General Assembly 2017 © Author(s) 2017. CC Attribution 3.0 License. How Does Intertropical Convergence Zone Variation Impact on Tropical Cyclone in the Northern Hemisphere? Liping Ma (1,2) and Richard Williams (2) (1) Chinese Academy of Meteorological Sciences, Beijing, China, (2) University of Liverpool, Department of Earth, Ocean & Ecological Sciences, School of Environmental Sciences, Liverpool, UK Enhanced sea surface temperature is expected to be favourable for more tropical cyclone formation. However, a surprising result emerges from the analysis of the frequency of tropical cyclones in the global tropical oceans in the northern hemisphere. The frequency of tropical cyclones positively correlates with a strengthening and northward movement of the Intertropical Convergence Zone (ITCZ hereafter). There is a different regional character for the tropical cyclones activity: in the Western North Pacific, the number of tropical cyclones has been decreasing since 1960s, whereas in the Eastern North Pacific and North Atlantic, the number of tropical cyclones has been increasing since 1949 and 1984 respectively. Most of the tropical cyclones in the tropical oceans are generated within the ITCZ (called the monsoon trough in the Western North Pacific, and the easterly wave in the Eastern North Pacific and North Atlantic). At the same time, there are changes in the strength and position of the ITCZ. In the Western North Pacific, ITCZ strength has been weakening and its position has been moving equatorward since the 1960s when the tropical cyclones frequency decreased. In the Eastern North Pacific, the ITCZ has been strengthening and moving northward where the tropical cyclone frequency has been increasing since 1949.
    [Show full text]
  • A Climate Network Perspective of the Intertropical Convergence Zone Frederik Wolf1,2, Aiko Voigt3,4, and Reik V
    https://doi.org/10.5194/esd-2020-81 Preprint. Discussion started: 6 November 2020 c Author(s) 2020. CC BY 4.0 License. A climate network perspective of the intertropical convergence zone Frederik Wolf1,2, Aiko Voigt3,4, and Reik V. Donner1,5 1Research Domain IV - Complexity Science, Potsdam Institute for Climate Impact Research (PIK) – Member of the Leibniz Association, Potsdam, Germany 2Department of Physics, Humboldt University, Berlin, Germany 3Institute of Meteorology and Climate Research, Department Troposphere Research, Karlsruhe Institute of Technology, Karlsruhe, Germany 4Lamont-Doherty Earth Observatory, Columbia University in the City of New York, NY, USA 5Department of Water, Environment, Construction and Safety, Magdeburg–Stendal University of Applied Sciences, Magdeburg, Germany Correspondence: Frederik Wolf ([email protected]) Abstract. The intertropical convergence zone (ITCZ) is an important component of the tropical rain belt. Climate models continue to struggle to adequately represent the ITCZ and differ substantially in its simulated response to climate change. Here we employ complex network approaches, which extract spatio-temporal variability patterns from climate data, to better understand differences in the dynamics of the ITCZ in state-of-the-art global circulation models (GCMs). For this purpose, 5 we study simulations with 14 GCMs in an idealized slab-ocean aquaplanet setup from TRACMIP – the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project. We construct network representations based on the spatial correlation pattern of monthly surface temperature anomalies and study the zonal mean patterns of different topological and spatial network characteristics. Specifically, we cluster the GCMs by means of their zonal network measure distribution utilizing hierarchical clustering.
    [Show full text]
  • Early Holocene Greening of the Sahara Requires Mediterranean Winter Rainfall
    Early Holocene greening of the Sahara requires Mediterranean winter rainfall Rachid Cheddadia,1,2, Matthieu Carréb,c,1, Majda Nourelbaitd, Louis Françoise,1, Ali Rhoujjatif, Roger Manayc, Diana Ochoac, and Enno Schefußg,1 aInstitut des Sciences de l’Évolution de Montpellier, CNRS, Institut de Recherche pour le Développement, University of Montpellier, 34000 Montpellier, France; bInstitut Pierre-Simon Laplace-Laboratoire d’Océanographie et du Climat: Expérimentations et approches numériques, CNRS, Institut de Recherche pour le Développement, Muséum National d’Histoire naturelle, Sorbonne Université (Pierre and Marie Curie University), 75006 Paris, France; cCentro de Investigaciòn Para el Desarrollo Integral y Sostenible, Laboratorios de Investigación y Desarrollo, Facultad de Ciencias y Filosofia, Universidad Peruana Cayetano Heredia, Lima 15102, Peru; dLGMSS, URAC45, University Chouaib Doukkali, El Jadida 24000, Morocco; eUR-SPHERES, University of Liège, 4000 Liège, Belgium; fLaboratoire Géoressources, URAC42, Université Cadi Ayyad, Marrakech 40000, Morocco; and gMARUM - Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany Edited by Francesco S. R. Pausata, University of Quebec in Montreal, Montreal, Canada, and accepted by Editorial Board Member Donald R. Ort April 20, 2021 (received for review December 17, 2020) The greening of the Sahara, associated with the African Humid the land surface (19–22). Reproducing the green Sahara has posed Period (AHP) between ca. 14,500 and 5,000 y ago, is arguably the a lasting challenge for climate modelers. The influence of the Af- largest climate-induced environmental change in the Holocene; it rican monsoon extends only to ∼24° N (with or without interactive is usually explained by the strengthening and northward expan- vegetation) in most Middle Holocene simulations, which is insuf- sion of the African monsoon in response to orbital forcing.
    [Show full text]
  • Interaction Between a Shear Line and the Inter Tropical Convergence Zone in the Northwestern Coast of Venezuela
    Interaction between a shear line and the Inter Tropical Convergence Zone in the Northwestern Coast of Venezuela. 25 November 2010 Heavy Rainfall Event Julio Cabanerit, INAMEH, Venezuela NCEP, College Park, MD, July 2016 This work describes the interaction between a shear line and the Inter Tropical Convergence Zone that produced heavy rains in a usually dry region of the northern coast of Venezuela. The event occurred during 25-30 November 2010 producing rainfall totals near 80% of the annual total in only six days. This generated severe flooding in the Coro, Falcon region in Venezuela. The short case study was conducted by Julio Cabanerit from INAMEH (Instituto Nacional de Meteorologia e Hidrología) as part of the WPC Tropical Desk Training carried out during the April-July 2016 period. Heavy rainfall events in the Northern Coast of Venezuela are rare. Climatologically, this region of the Caribbean is characterized by a persistent low-level divergent wind pattern in association with the entrance of the South Caribbean Low-Level jet. This jet also provides enhanced low-level shear that often disintegrates deep convective structures rather than enhancing them. Active deep convection over the continent usually leads to subsidence along the southern Caribbean, which further limits the development of deep convection and large rainfall accumulations. The image presented in this slide is a Multisatellite Precipitation Analysis produced at NASA’s Goddard Space Flight Center using data from the TRMM (Tropical Rainfall Measuring Mission) satellite. It shows rainfall totals of 200-350mm in the northern coast of Venezuela over the 25-30 November 2010 period.
    [Show full text]