DOCSLIB.ORG

Orographic Effect on the Summer

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Orographic Effect on the Summer Orographic Effects on South China Sea Summer Climate Haiming Xu∗ Department of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing, China Shang-Ping Xie and Yuqing Wang International Pacific Research Center and Department of Meteorology, University of Hawaii, Hawaii, USA Wei Zhuang, and Dongxiao Wang LED，South China Sea Institute of Oceanology, Chinese Academy of Science, Guangzhou, China Submitted to Meteorology and Atmospheric Physics April, 2007 ∗ Corresponding author address: Dr. Haiming Xu, Department of Atmospheric Sciences, Nanjing University of Information Science and Technology, 114 New Street, Pancheng, Pukou District, Nanjing 210044, China. E-mail: [email protected] Abstract New satellite observations reveal several distinct features of the South China Sea (SCS) summer climate: an intense low-level southwesterly wind jet off the coast of South Vietnam, a precipitation band on the western flank of the north-south running Annam mountain range, and a rainfall shadow to the east in the western SCS off the east coast of Vietnam. A high-resolution full-physics regional atmospheric model is used to investigate the mechanism for the formation of SCS summer climate. A comparison of the control model simulation with a sensitivity experiment with the mountain range artificially removed demonstrates that the aforementioned features form due to orographic effects of the Annam mountains. Under the prevailing southwesterly monsoon, the mountain range forces the ascending motion on the windward and subsidence on the lee side, giving rise to bands of active and suppressed convection, respectively. On the south edge of the mountain range, the southwesterlies are accelerated to form an offshore low-level wind jet. The mid-summer cooling in the SCS induced by this wind jet further helps reduce precipitation over the central SCS. A reduced-gravity ocean model is used to investigate the ocean response to the orographically induced wind forcing, which is found to be important for the formation of the double-gyre circulation observed in the summer in SCS, in particular for the northern cyclonic circulation. Thus, orography is a key to shaping the SCS summer climate both in the atmosphere and in the ocean. 1. Introduction The South China Sea (SCS) is a large semi-enclosed marginal ocean basin with a total area of 3.5 million km2. It is connected to the East China Sea to the northeast, the Pacific Ocean to the east, and the Indian Ocean to the southwest. The SCS climate is part of the East Asian monsoon system [Lau et al., 1998]. In winter the SCS is dominated by the strong northeasterly monsoon while in summer the winds reverse the direction to southwesterly [e.g., Liu and Xie, 1999]. It is well known that in summer the southwesterly winds reach a maximum east of Ho Chi Minh City [e.g., Xie et al., 2002]. Figure 1a shows the summer surface wind climatology along with land topography over the Indochina peninsula. A narrow mountain range, called the Annam cordillera, runs in a north-south direction on the east coast of Indochina peninsula on the Vietnam-Laos borders and ends just north of Ho Chi Minh City. Noting that the SCS wind jet is located just offshore of the south edge of the Annam cordillera, Xie et al. [2003] suggest that the orographic blockage of the southwesterly monsoon and the wind acceleration at the south corner of the mountain range are the cause of the wind jet. They go on to show that the strong curls of this wind jet are the major drive of the summer SCS circulation, giving rise to a number of important climatic features of the region such as a cold upwelling filament [Huang et al., 1994; Kuo et al., 2000] that disrupts the summer warming. The wind jet varies with the El Nino/Southern Oscillation (ENSO), driving interannual variability of the SCS in both ocean circulation and sea surface temperature (SST). While plausible, the orographic hypothesis of Xie et al. [2003] has never been rigorously 1 tested in numerical models. The Annam cordillera also leaves a clear signature on precipitation. Figure 1b shows the summer precipitation climatology in the region. As the southwesterly monsoon impinges on the mountain range, the rising motion creates a windward rain band and the subsequent subsidence produces a rain shadow on the lee. Such orographic rain bands are also observed on the west coasts of Myanmar, Thailand, Cambodia, and the Philippines. With a numerical experiment, Xie et al. [2006] suggest that such orographic rain bands are not simply a local phenomenon but exert important remote influences on the continental monsoon because of strong interaction between circulation and convection in the region during summer. The Annam cordillera is more than 500 m high on average but only 200 km or less in width, posing a serious problem for numerical simulations. With typical horizontal resolution of 2-3o, the current global general circulation models represent the Annam mountain range poorly and fail to simulate either the SCS wind jet or the orographic rain band/shadow (not shown). The summer circulation of the central SCS is dominated by a double-gyre circulation, with an eastward inter-gyre jet in between that advects the cold coastal water to form the cold filament east of south Vietnam. This pair of anticyclonic and cyclonic gyres south and north of roughly 12oN are observed from in-situ current measurements [Fang et al., 2002] and satellite altimetry [Shaw et al. 1999; Ho, et al., 2000]. With its strong wind curls, the orographic-induced southwest wind jet is considered to be the major cause of this double-gyre circulation pattern [Xie et al., 2 2003; Gan et al., 2006; Wang et al., 2006]. The present study test the above orographic hypothesis for the formation of the wind jet and the couplet of the rain band and shadow in the summer SCS by using a high-resolution regional atmospheric model. The 0.2º grid size of the model is equivalent to T520 resolution for a global spectral model. Our results show that indeed, the Annam cordillera exerts a great influence on the wind and precipitation distributions over the Indochina peninsula and SCS. We further apply the atmospheric model results to assess the orographic effect on ocean circulation using a reduced-gravity ocean model. We find a strong effect on the northern cyclonic gyre north of the wind jet. The rest of the paper is organized as follows. Section 2 describes the regional atmospheric model, experimental design, and observational data sets used for verification. Section 3 presents the atmospheric simulation results and investigates the orographic effects of the Annam mountain range. Section 4 describes the ocean model and presents the experiment results. Section 5 presents a summary and discussion. 2. Regional Atmospheric Model and Experimental Design 2.1. Atmospheric Model The regional atmospheric model (RAM) developed at the International Pacific Research Center (IPRC), University of Hawaii, is used in this study. It is a primitive equation model with sigma as the vertical coordinate, solved on a longitude-latitude grid system. The model domain is 5ºS-25ºN, 90º-135ºW, including the SCS, Indochina peninsula, east part of the Bay of Bengal, and part of the western Pacific 3 (Fig. 2). The model uses a grid spacing of 0.2º in both longitude and latitude, and has 28 levels in the vertical. A detailed description of the model and its performance in simulating regional climate of East Asia can be found in Wang et al. [2003]. The model has also been used to simulate the regional climate over the eastern Pacific, including the atmospheric response to tropical instability ocean waves [Small et al., 2003], boundary layer clouds over the southeast Pacific [Wang et al., 2004], the effects of the Andean and Central American mountains [Xu et al., 2004; Xu et al., 2005], and more recent the diurnal cycle of precipitation over the Maritime continent region (Zhou and Wang 2006; Wang et al. 2007). The model includes a detailed cloud microphysics scheme for grid-scale moist processes [Wang, 2001]. The mixing ratios of cloud water, rainwater, cloud ice, snow, and graupel are all prognostic variables in the model. Condensation (evaporation) of cloud water takes place instantaneously when the air is supersaturated (subsaturated). Subgrid-scale convective processes, such as shallow convection, midlevel convection, and penetrative deep convection, are considered based on the mass flux cumulus parameterization scheme originally developed by Tiedtke [1989] and later modified by Nordeng [1995]. The subgrid-scale vertical mixing is accomplished by the so-called E⎯ε closure scheme, in which both the turbulence kinetic energy (TKE) and its dissipation rate are prognostic variables [Detering and Etling, 1985]. Turbulent fluxes at the ocean surface are calculated using the TOGA COARE algorithm [Fairall et al., 1996; Wang 2002]. Over the land, the bulk aerodynamic method is used in the land surface model, 4 which uses the Biosphere-Atmosphere Transfer Scheme [Dickinson et al., 1993]. Soil moisture is initialized using a method described by Giorgi and Bates [1989] such that the initial soil moisture depends on the vegetation and soil type defined for each grid cell. The radiation package originally developed by Edwards and Slingo [1996] and later modified by Sun and Rikus [1999] is used, which includes seven/four bands for longwave/shortwave radiation. Seasonal-varying climatological ozone and a constant mixing ratio of carbon dioxide for the present climate are used. 2.2. Experimental Design The initial and lateral boundary conditions are obtained from the National Centers for the Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis [Kalnay et al., 1996], available on a 2.5º×2.5º grid with 17 vertical pressure levels.
Load more

Recommended publications
  • (Highresmip V1.0) for CMIP6
    High Resolution Model Intercomparison Project (HighResMIP v1.0) for CMIP6 1 2 3 5 Reindert J. Haarsma , Malcolm Roberts , Pier Luigi Vidale , Catherine A. Senior2, Alessio Bellucci4, Qing Bao5, Ping Chang6, Susanna Corti7, Neven S. Fučkar8, Virginie Guemas8, Jost von Hardenberg7, Wilco Hazeleger1,9,10, Chihiro Kodama11, Torben Koenigk12, Lai-Yung Ruby Leung13, Jian Lu13, Jing-Jia Luo14, Jiafu Mao15, Matthew S. Mizielinski2, Ryo Mizuta16, Paulo Nobre17, Masaki 18 4 19 20 10 Satoh , Enrico Scoccimarro , Tido Semmler , Justin Small , Jin-Song von Storch21 1Royal Netherlands Meteorological Institute, De Bilt, The Netherlands 2Met Office Hadley Centre, Exeter, UK 15 3University of Reading, Reading, UK 4 Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy 5LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing , China P.R. 6Texas A&M University, College Station, Texas, USA 7National Research Council – Institute of Atmospheric Sciences and Climate, Italy 20 8Barcelona Super Computer Center, Earth Sciences Department, Barcelona, Spain 9Netherlands eScience Center, Amsterdam, The Netherlands 10Wageningen University, The Netherlands 11Japan Agency for Marine-Earth Science and Technology, Japan 12Swedish Meteorological and Hydrological Institute, Norrköping, Sweden 25 13Pacific Northwest National Laboratory, Richland, USA 14Bureau of Meteorology, Australia 15Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, USA 16Meteorological Research Institute,
    [Show full text]
  • Computer Models, Climate Data, and the Politics of Global Warming (Cambridge: MIT Press, 2010)
    Complete bibliography of all items cited in A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming (Cambridge: MIT Press, 2010) Paul N. Edwards Caveat: this bibliography contains occasional typographical errors and incomplete citations. Abbate, Janet. Inventing the Internet. Inside Technology. Cambridge: MIT Press, 1999. Abbe, Cleveland. “The Weather Map on the Polar Projection.” Monthly Weather Review 42, no. 1 (1914): 36-38. Abelson, P. H. “Scientific Communication.” Science 209, no. 4452 (1980): 60-62. Aber, John D. “Terrestrial Ecosystems.” In Climate System Modeling, edited by Kevin E. Trenberth, 173- 200. Cambridge: Cambridge University Press, 1992. Ad Hoc Study Group on Carbon Dioxide and Climate. “Carbon Dioxide and Climate: A Scientific Assessment.” (1979): Air Force Data Control Unit. Machine Methods of Weather Statistics. New Orleans: Air Weather Service, 1948. Air Force Data Control Unit. Machine Methods of Weather Statistics. New Orleans: Air Weather Service, 1949. Alaka, MA, and RC Elvander. “Optimum Interpolation From Observations of Mixed Quality.” Monthly Weather Review 100, no. 8 (1972): 612-24. Edwards, A Vast Machine Bibliography 1 Alder, Ken. The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World. New York: Free Press, 2002. Allen, MR, and DJ Frame. “Call Off the Quest.” Science 318, no. 5850 (2007): 582. Alvarez, LW, W Alvarez, F Asaro, and HV Michel. “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction.” Science 208, no. 4448 (1980): 1095-108. American Meteorological Society. 2000. Glossary of Meteorology. http://amsglossary.allenpress.com/glossary/ Anderson, E. C., and W. F. Libby. “World-Wide Distribution of Natural Radiocarbon.” Physical Review 81, no.
    [Show full text]
  • Aerosol-Orography-Precipitation – a Critical Assessment T Goutam Choudhurya, Bhishma Tyagia,*, Jyotsna Singhb, Chandan Sarangic, S.N
    Atmospheric Environment 214 (2019) 116831 Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv Review article Aerosol-orography-precipitation – A critical assessment T Goutam Choudhurya, Bhishma Tyagia,*, Jyotsna Singhb, Chandan Sarangic, S.N. Tripathid a Department of Earth and Atmospheric Sciences, National Institute of Technology Rourkela, Rourkela, 769008, Odisha, India b Shanti Raj Bhawan, Paramhans Nagar, Kandwa, Varanasi, 221106, India c Pacific Northwest National Laboratory, Richland, United States d Department of Civil Engineering & Department of Earth Sciences, Indian Institute of Technology Kanpur, Kanpur, 208016, India GRAPHICAL ABSTRACT ARTICLE INFO ABSTRACT Keywords: The increasing anthropogenic pollution and its interaction with precipitation received much attention from the Aerosols research community and have been explored extensively for understanding the aerosol-cloud interactions. The Aerosol-orography-precipitation interactions impacts of orography and aerosols on the precipitation processes have unveiled the Aerosol-Orography- Cloud microphysics Precipitation (AOP) interaction as an essential research area. The understanding of AOP interaction is critical for Spillover effect improving the extreme rainfall events prediction over mountainous regions. The phase of clouds (warm or Orographic enhancement factor mixed) along with orography has emerged as a significant factor for influencing the AOP relations. The present work reviews the modelling and observational based studies dealing with the relationship between orography and aerosols on the precipitation. The study reveals the principal role of aerosols in shifting the precipitation pattern for orographic regions. The environmental factors, especially ambient temperature, humidity and flow patterns are also identified to affect the orographic precipitation. The review also discovers that AOP studies exist only to limited areas of the world due to limited observations, and mostly with idealised cases in the modelling framework.
    [Show full text]
  • What Even Is 'Climate'?
    Geosci. Commun. Discuss., https://doi.org/10.5194/gc-2018-11 Manuscript under review for journal Geosci. Commun. Discussion started: 13 July 2018 c Author(s) 2018. CC BY 4.0 License. What even is ‘Climate’? Oliver Bothe1 1Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Max-Planck-Strasse 1, 21502, Geesthacht, Germany Correspondence: Oliver Bothe ([email protected], [email protected]) Abstract. Although the concept of climate is easy to understand, there is not any uncontroversial definition of it. Most def- initions fall back to the simple formulation that ‘climate is the statistics of weather’. Recent attempts at a definition called versions of this saying vague. Climate is policy-relevant, and discussions on climate and climate change benefit from clarity on the topic. Beyond the policy relevance a definition should also be valid for scientific purposes and for individual views. It 5 has to account for a general concept and individual instances of climate. Here, I try to highlight why the flexibility and the immediacy of the colloquial definition fit the topic. This defence shifts the lack of a clear definition towards the term ‘weather’ and the time-scales separating weather and climate. 1 Introduction “Climate is what you expect, weather is what you get” (e.g., Geographical Association and London Geographical Institute, 10 1902; Lorenz, unpublished). Or: “Climate is the statistics of weather” (e.g., McBean et al., 1992; Easterling et al., 1999; Farmer, 2014; Molua and Lambi, 2007; von Storch, 2004; Roe and O’Neal, 2009; Roe, 2009). Public discourse and scientific literature frequently use versions of these colloquial sayings.
    [Show full text]
  • Southern African Orography Impacts on Low Clouds and the Atlantic ITCZ
    PUBLICATIONS Geophysical Research Letters RESEARCH LETTER Southern African orography impacts on low clouds 10.1002/2017GL073098 and the Atlantic ITCZ in a coupled model Key Points: S. F. Potter1 , E. J. Dawson2, and D. M. W. Frierson2 • Namibian stratocumulus deck thins fi signi cantly due to the removal of 1Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington, USA, southern African orography 2 • Atlantic ITCZ shifts south due to the Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA increase in temperature resulting from the reduction of Namibian low clouds • Use of a coupled model allows ocean Abstract We examine the influence of southern African orography on the Namibian stratocumulus deck, circulation to cool the South Atlantic, the South Atlantic ocean-to-atmosphere energy transport, and the Intertropical Convergence Zone (ITCZ), which lessens and changes the structure of the ITCZ shift using an atmosphere-only model and a coupled atmosphere-ocean model. For both models, a control simulation with realistic orography is compared to a simulation where the orography in southern Africa was removed. As in the previous studies, the removal of orography results in thinning of the Namibian stratocumulus deck. In the coupled model, the increased sea surface temperature in the southern Atlantic Correspondence to: S. F. Potter, due to the reduction of low clouds forces the Atlantic ITCZ to shift southward toward the warmer [email protected] hemisphere. However, changes in the ocean circulation cool the South Atlantic atmosphere, lessening the ITCZ shift and changing the structure of precipitation. These results show the importance of orography on Citation: shaping Atlantic rainfall and highlight the role of dynamical ocean processes in atmospheric dynamics.
    [Show full text]
  • The Impacts of Topography on Spatial and Temporal Rainfall Distribution Over Rwanda Based on WRF Model
    Atmospheric and Climate Sciences, 2016, 6, 145-157 Published Online April 2016 in SciRes. http://www.scirp.org/journal/acs http://dx.doi.org/10.4236/acs.2016.62013 The Impacts of Topography on Spatial and Temporal Rainfall Distribution over Rwanda Based on WRF Model Didier Ntwali1,2,3*, Bob Alex Ogwang4,5, Victor Ongoma4 1Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 2University of Chinese Academy of Sciences, Beijing, China 3Rwanda Meteorology Agency, Ministry of Natural Resources (MINIRENA), Kigali, Rwanda 4Nanjing University of Information, Science and Technology, Nanjing, China 5Uganda National Meteorological Authority, Kampala, Uganda Received 13 January 2016; accepted 26 February 2016; published 1 March 2016 Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecast- ing (WRF-ARW) model was used to study two historical cases of heavy rainfall which took place over Rwanda during two rain seasons, March to May (MAM) and September to December (SOND), from April 7 to 9, 2012 (for MAM) and from October 29 to 31, 2012 (during SOND). The control experiment was done with actual topography, whereas sensitivity experiment was carried out with topography reduced by half. Results show that rainfall distribution over Rwanda significantly changes when topography is reduced. The reduction in topography leads to a decrease in rainfall amounts in both MAM and SOND seasons, with varying magnitudes.
    [Show full text]
  • The Interaction of Precipitation with Orography (IPRO) AGENDA
    ASP Summer Colloquium 2017 (June 4-16), NCAR The Interaction of Precipitation with Orography (IPRO) AGENDA Mornings will be in the Fleischmann Building (FB), Afternoons in the Damon Room (DR) and occasionally in the Mesa Lab Main Seminar Room (ML) Sunday, 4 June Location 5:00 pm Icebreaker and Welcome Williams Village North (in Lobby) Rich Neale and Val Sloan (NCAR) 5:30 pm Dinner at WVC Dining Hall Williams Village Center 6:30 pm Rich Neale Overview of Colloquium and Goals Talks Tim Barnes The History of NCAR 7:45 pm Rich Neale Final Remarks Return to dorms Monday, 5 June Location 8:30 am Rich Neale (NCAR) Welcome and Logistics FB 8:45 am Jim Hurrell (NCAR director) NCAR welcome FB 9:15 am Rich Neale (NCAR) IPRO: Overview of precipitation and orography: FB Observations, modeling and impacts 10:15 am Break 10:45 am Andrew Newman (NCAR) Producing observational precipitation datasets over FB orography in the US 11:45 am Lunch Including small weather trail hike 1:30 pm Kelly Mahoney (NOAA) Extreme Precipitation and Severe Weather in the Front FB Range 2:30 pm Project time FB/DR Cecile Hannay (NCAR) The Community Earth System Model (CESM) Michael Duda (NCAR) The Weather Research and Forecasting Model (WRF) 3:15 pm Break 3:45pm Project time DR Rory Kelly (CISL) Establishing local and supercomputing work environments for projects 5:00 pm Adjourn Tuesday, 6 June Location 8:30 am Angie Pendergrass (NCAR) Global Precipitation Statistics FB 9:30 am Brian Mapes (U. Miami) North American Monsoon Experiment (NAME) FB 10:30 am Break 11:00 am Nicholas Siler (U Washington) Orographic Rain Shadows FB 12:00 pm Lunch (opportunity to chat with speakers) 1:00 pm Meet for short hike 1:30 pm Project time: Running CESM and setting up case studies DR ​ 3:30 pm Break 5:00 pm Adjourn Wednesday, 7 June Location 8:30 am Kristen Rasmussen (Colo.
    [Show full text]
  • The Direct and Ocean-Mediated Influence of Asian Orography On
    Climate Dynamics https://doi.org/10.1007/s00382-019-04615-5 The direct and ocean‑mediated influence of Asian orography on tropical precipitation and cyclones Jane Wilson Baldwin1 · Gabriel A. Vecchi2 · Simona Bordoni3 Received: 8 June 2018 / Accepted: 4 January 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Prior global climate model (GCM) experiments have shown that the Tibetan Plateau and related orography play a significant role in enhancing the Indian Monsoon, particularly during its onset, and the East Asian monsoon. However, these experiments have been largely performed with atmosphere-only, lower-resolution GCMs that neglect the influence of atmosphere–ocean coupling, and do not resolve tropical cyclones (TCs). Here we explore the influence of Asian orography on tropical circula- ∼ tions in a Geophysical Fluid Dynamics Laboratory GCM at two different atmosphere/land resolutions ( 50 and 200 km), and with or without atmosphere–ocean coupling. Atmosphere–ocean coupling is found to play a significant role in the precipita- tion response due to the Asian orography, enhancing the precipitation increase over the Western North Pacific (hereafter WNP), and drying the Arabian Sea. In these same regions, the higher resolution model, which resolves TCs up to category 3, suggests that Asian orography has a significant influence on TCs, increasing TC frequency in the WNP, and decreasing it in the Arabian Sea. However, in contrast to precipitation, this TC response does not appear to be strongly affected by the atmosphere–ocean coupling. Connections between the direct atmospheric circulation response to Asian orography, ocean circulation changes, and these various effects on precipitation and tropical cyclones are analyzed and discussed.
    [Show full text]
  • Learning About Precipitation Orographic Enhancement from Snow-Course Data Improves Water-Balance Modeling
    https://doi.org/10.5194/hess-2020-571 Preprint. Discussion started: 26 November 2020 c Author(s) 2020. CC BY 4.0 License. Learning about precipitation orographic enhancement from snow-course data improves water-balance modeling Francesco Avanzi1, Giulia Ercolani1, Simone Gabellani1, Edoardo Cremonese2, Paolo Pogliotti2, Gianluca Filippa2, Umberto Morra di Cella2,1, Sara Ratto3, Hervè Stevenin3, Marco Cauduro4, and Stefano Juglair4 1CIMA Research Foundation, Via Armando Magliotto 2, 17100 Savona, Italy 2Climate Change Unit, Environmental Protection Agency of Aosta Valley, Loc. La Maladière, 48-11020 Saint-Christophe, Italy 3Regione Autonoma Valle d’Aosta, Centro funzionale regionale, Via Promis 2/a, 11100 Aosta, Italy 4Direzione Operativa Operations, C.V.A. S.p.A., Via Stazione 31, 11024 Châtillon, Italy Correspondence: Francesco Avanzi ([email protected]) Abstract. Precipitation orographic enhancement depends on both synoptic circulation and topography. Since high-elevation headwaters are often sparsely instrumented, the magnitude and distribution of this enhancement remain poorly understood. Filling this knowledge gap would allow a significant step ahead for hydrologic-forecasting procedures and water management in general. 5 Here, we hypothesized that spatially distributed, manual measurements of snow depth (courses) could provide new insights into this process. We leveraged 11,000+ snow-course data upstream two reservoirs in the Western European Alps (Aosta Valley, Italy) to estimate precipitation orographic enhancement in the form of lapse rates and consequently improve predictions of a snow-hydrologic modeling chain (Flood-PROOFS). We found that Snow Water Equivalent (SWE) above 3000 m ASL was between 2 and 8.5 times higher than recorded cumulative seasonal precipitation below 1000 m ASL, with gradients up to 1000 1 10 mm w.e.
    [Show full text]
  • New Possible Mechanisms of Thunderstorm Clouds Physics Manana Kachakhidze, Nino Kachakhidze-Murphy Georgian Technical University
    New Possible Mechanisms of Thunderstorm Clouds Physics Manana Kachakhidze, Nino Kachakhidze-Murphy Georgian Technical University, Faculty of Informatics and Management Systems Correspondence to: [email protected] Abstract The work provides possible mechanisms of physics of thunderstorm clouds. We tried to consider the problems of the hail clouds in a completely different view. The article is based on the latest scientific achievement of modern theoretical physics, chemistry, physics of thunderstorms clouds and gives opportunities for new ways searching of impact on hail clouds. Introduction It is known that a strong earthquake preparation process can be accompanied by various geophysical anomalies, which expose themselves several months, weeks or days prior to earthquakes. Such as: Changing of intensity of electro-telluric current in focal area; Perturbations of geomagnetic field in forms of irregular pulsations or regular short-period pulsations; Perturbations of atmospheric electric field; Irregular changing of characteristic parameters of the lower ionosphere (plasma frequency, electron concentration, height of D layer, etc.); Irregular perturbations reaching the upper ionosphere, namely F2-layer, for 2-3 days before the earthquake; Increased intensity of electromagnetic emissions in upper ionosphere in several hours or tenths of minutes before earthquake; Lighting before earthquake; Infrared radiation; Total Electron Content (TEC) anomalies; Changing of weather parameters. Physical mechanisms of the mentioned phenomena by us are explained on the base of the classical electrodynamics [16]. As it was expected, in the origination of the above mentioned anomalies the defining role electromagnetic radiation plays. Exceptions are not the case of cloudiness intensification, which, of course, implies a good weather change with the "bad weather".
    [Show full text]
  • Temporal and Spatial Study of Thunderstorm Rainfall in the Greater Sydney Region Ali Akbar Rasuly University of Wollongong
    University of Wollongong Research Online University of Wollongong Thesis Collection University of Wollongong Thesis Collections 1996 Temporal and spatial study of thunderstorm rainfall in the Greater Sydney region Ali Akbar Rasuly University of Wollongong Recommended Citation Rasuly, Ali Akbar, Temporal and spatial study of thunderstorm rainfall in the Greater Sydney region, Doctor of Philosophy thesis, School of Geosciences, University of Wollongong, 1996. http://ro.uow.edu.au/theses/1986 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] TEMPORAL AND SPATIAL STUDY OF THUNDERSTORM RAINFALL IN THE GREATER SYDNEY REGION A thesis submitted in fulfilment of the requirements for the award of the degree UNIVERSITY O* DOCTOR OF PHILOSOPHY from UNIVERSITY OF WOLLONGONG by ALIAKBAR RASULY B.Sc. & M.Sc. (IRAN, TABRIZ University) SCHOOL OF GEOSCIENCES 1996 CERTIFICATION The work presented herein has not been submitted to any other university or institution for a higher degree and, unless acknowledged, is my own original work. A. A. Rasuly February 1996 i ABSTRACT Thunderstorm rainfall is considered as a very vital climatic factor because of its significant effects and often disastrous consequences upon people and the natural environment in the Greater Sydney Region. Thus, this study investigates the following aspects of thunderstorm rainfall climatology of the region between 1960 to 1993. In detail, it was found that thunderstorm rainfalls in Sydney have marked diurnal and seasonal variations. They are most frequent in the spring and summer and during the late afternoon and early evening. Thunderstorms occur primarily over the coastal areas and mountains, and less frequently over the lowland interior of the Sydney basin.
    [Show full text]
  • Revisiting the Role of Mountains in the Northern Hemisphere Winter Atmospheric Circulation
    JULY 2021 W H I T E E T A L . 2221 Revisiting the Role of Mountains in the Northern Hemisphere Winter Atmospheric Circulation a b b R. H. WHITE, J. M. WALLACE, AND D. S. BATTISTI a Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada b Department of Atmospheric Sciences, University of Washington, Seattle, Washington (Manuscript received 30 September 2020, in final form 9 April 2021) ABSTRACT: The impact of global orography on Northern Hemisphere wintertime climate is revisited using the Whole Atmosphere Community Climate Model, version 6 (WACCM6). A suite of experiments explores the roles of both resolved orography and the parameterized effects of unresolved orographic drag (hereafter parameterized orography), including gravity waves and boundary layer turbulence. Including orography reduces the extratropical tropospheric and stratospheric zonal mean zonal wind U by up to 80%; this is substantially greater than previous estimates. Ultimately, parameterized orography accounts for 60%–80% of this reduction; however, away from the surface most of the forcing of U by param- eterized orography is accomplished by resolved planetary waves. We propose that a catalytic wave–mean-flow positive feedback in the stratosphere makes the stratospheric flow particularly sensitive to parameterized orography. Orography and land–sea contrast contribute approximately equally to the strength of the midlatitude stationary waves in the free tropo- sphere, although orography is the dominant cause of the strength of the Siberian high and Aleutian low at the surface and of the position of the Icelandic low. We argue that precisely quantifying the role of orography on the observed stationary waves is an almost intractable problem, and in particular should not be approached with linear stationary wave models in which U is prescribed.
    [Show full text]