Influence of South America orography on summertime precipitation in Southeastern South America
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Impacts of the main South American orographic structures (the Andes, the Brazilian Plateau and the Guiana shield) on the regional climate and associated global teleconnection are investigated through numerical experiments in which some of these features are suppressed. Simulations are performed with a ‘‘two-way nesting’’ system coupling interactively the regional and global versions of the LMDZ4 atmospheric general circulation model. At regional scale, the simulations confirm previous studies, showing that both the Andes and the Brazilian Plateau exert a control on the position and strength of the South Atlantic convergence zone (SACZ), mainly through their impact on the low-level jet and the coastal branch of the subtropical anticyclones. The northern topography of South America appears to be crucial to determine the leading mode of rainfall variability in eastern South America, which manifests itself as a dipole-like pattern between Southeastern South America and the SACZ region. The suppression of South America orography also shows global-scale effects, corresponding to an adjustment of the global circulation system. Changes in atmospheric circulation and precipitation are found in remote areas on the globe, being the consequences of various teleconnection mechanisms. When the Brazilian Plateau and the Andes are suppressed, there is a decrease of precipitation in the SACZ region, associated with a weakening of the large-scale ascendance. Changes are described in terms of anomalies in the Walker circulation, meridional displacements of the mid-latitude jet stream, Southern annular mode anomalies and modifications of Rossby wave train teleconnection processes.
KeywordsSouth America orography Summer precipitation Orography influence Two-way nesting system Global teleconnection processes
Comments and suggestions provided by three anonymous reviewers were very helpful in improving this paper. This research was supported by the European Commission’s Seventh Framework Programme (FP7/2007–2013) under Grant Agreement No 212492 (CLARIS LPB. A Europe-South America Network for Climate Change Assessment and Impact Studies in La Plata Basin), ECOS-MINCyT (project No A12U02 DIAGAC), CNRS/LEFE Program, and CONICET PIP 112-200801-00399. The first author C.J. was supported by a Ph.D grant from the Ecole Polytechnique, and post-doc grants from the Institute of Research for the Development (IRD), the French National Center for Scientific Research (CNRS), and the Ecole Polytechnique. We especially thank François Lott, Frédéric Hourdin and our other colleagues from the LMD (Laboratoire de Météorologie Dynamique) for the productive discussions about the experiments.
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