Climate Change and Climatic Variability in Latin America and the Caribbean
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both interannual and decadal ENSO-like climate variations yield wetter subtropics (when the ENSO-like indexes are in positive, El Niño–like phases) and drier midlatitudes and tropics (overall) over the Americas, in response to equatorward shifts in westerly winds and storm tracks in both hemispheres (Dettinger and others 2001).
South America A complex variety of regional and remote factors contributes to the climate of South America (Nogués-Paegle and others 2002). The tropospheric upper levels are characterized by high pressure centered over Bolivia and low pressure centered over northeast Brazil. At low levels the Andes effectively block air exchanges with the Pacific Ocean, but a continental-scale gyre transports moisture from the tropical Atlantic Ocean to the Amazon region and then southward toward extratropical South America. The South American low-level jet starts a regional intensification of this flow, channeling it along the eastern foothills of the Andes into the so-called Chaco low.4 The LLJ carries significant moisture from the Amazonas toward southern South America, and it is present throughout the year, but strongest during the austral winter season (Berbery and Collini 2000; Vernekar, Kirtman, and Fennessy 2003). A clear warm season precipitation maximum, associated with the South American Monsoon System (SAMS), dominates the mean seasonal cycle of precipitation in tropical and subtropical latitudes. The rainfall over northern South America is directly influenced by east-west circulation patterns, and consequently tropical sea surface temperature anomalies affect regions such as the Ecuador coast and north-northeast Brazil.5 The SAMS is also modulated by incursions of drier and cooler air from the midlatitudes over the interior of subtropical South America (Garreaud 2000; Vera and Vigliarolo 2000). Rainfall anomalies over subtropical South America are associated with regional feedback processes and interactions among the topography, the SAMS, and the midlatitude systems. Another important feature, a regional part of the ITCZ, is the South Atlantic Convergence Zone (SACZ)—a southeastward extension of cloudiness and precipitation from southern Amazonas toward southeast Brazil and the neighboring Atlantic Ocean. The SACZ reaches its easternmost position during December, in association with high precipitation over much of Brazil, a southeasterly flow over eastern Bolivia, and low precipitation in the Altiplano. The variability of precipitation during the austral summer