Can easterly winds in Southern Hemisphere mid-latitudes cause extreme daily precipitation over Patagonia?

E. A. AGOSTA, P. B. MARTIN Y L. SERIO

Viena

Conferencia; EGU General Assembly; 2018

Patagonia is a vast region in South America?s mid-latitudes, which encompasses two regions with highly distinctprecipitation features. They include wet Western Patagonia extending from the Pacific coast to the Andean highs,and dry Eastern Patagonia situated leeward of the Andes in the Argentine steppe plains. The prevailing westerlywinds throughout the year are responsible for the spatial distribution of mean precipitation. The climate of theArgentinean Eastern Patagonia is characterized by the extremely dryness of the air, because of low rainfalls andhigh evaporation as a consequence of strong westerly winds. At climatic scale, enhanced (reduced) monthly meanprecipitation is associated with weakened (intensified) westerly flow in the region. For such a reason, westerlieshave been considered the unique driver of climate both in Western and Eastern Patagonia.Extreme daily precipitation events are examined in detail to identify their typical synoptic tropospheric circulationflows. Intense daily precipitation is related partly to strong local westward moisture transport, as a consequence ofslow-moving weather systems crossing over eastern Patagonia. It could be interpreted as due to enhanced synopticeasterly moisture flux from the Atlantic. Thus, the westerlies rule was broken at least under blocking-like flows,which induces moist easterlies. The influence of the Peruvian coastal manifestation of the El Niño-SouthernOscillation (ENSO) phenomenon is discussed too.