''Easterlies'': induced precipitation in eastern Patagonia. Seasonal influences of ENSO'S FLAVOURS and SAM

Abstract

The seasonal influence of the phases of El Niño-Southern Oscillation (ENSO) and of Southern Annular Mode (SAM) on precipitation over eastern Patagonia is examined. Also, their impact in generating persistent daily easterly moisture flux leading to daily precipitation events. The significant signatures of the drivers on precipitation are found in March–April–May (MAM), June–July–August (JJA) for ENSO and November–December–January (NDJ) for SAM. Over the east coast, precipitation is mainly favoured owing to an overall growth of the seasonal mean number of precipitation days (~30%) by central Niño in JJA and by negative SAM phase in NDJ, and growth of the frequency of persistent events of daily westward moisture flux (~90%) by eastern Niña in MAM. A great spatial variability shapes the anomalies. Evidence is shown for weakened seasonal westerlies linked to Eastern Pacific Niño in MAM. Enhanced daily easterlies with net daily westward moisture flux in the region lead to strong daily precipitation. Growth in precipitation intensity in the northeast coast is also associated with Eastern Pacific Niño in MAM. In the interior lands, south of 45°S, westward moisture flux is increased up to ~200% by negative SAM phase in NDJ. The nature of extratropical low-frequency transient eddies travelling over the South Pacific will influence the frequency and intensity of daily local precipitation as well as the persistent westward flux during ENSO events.