CONICET | Buscador de Institutos y Recursos Humanos

The relationship between daily precipitation and unusually persistent easterly wind recorded at station level in the coast of Eastern Patagonia is examined. Despite an event of easterly winds persistent for more than 20 hr (E) is infrequent in Comodoro Rivadavia (CMR), about 80% of the times when it happened, it rained with daily precipitation over 1 mm; and near 30% of the times when it happened, it rained as an event of easterly winds persistent for two or more days (2E) with precipitation over 75th percentile.A precipitation day (P>= 1 mm) in weather context of 2E is defined as a daily P1&2E. The occurrence of P1&2E is far from randomness for most stations. The probability of null precipitation days with westerlies was higher than 95% on average among the stations. For daily P1&2E events in CMR, the convergence of westward moisture flux from the Atlantic is key. Its daily frequency shifts toward Niño (44%), followed by the Neutral (32%), and Niña (25%). The tropospheric circulation anomalous conditions are characterized by a blocking-like flow along 80-90ºW, with anticyclonic anomalies near 60º-70ºS and cyclonic anomalies in the mid-latitudes. The strength of the anomalies is given by the meridional gradient of tropospheric circulation anomalies, stronger during the Niño phase. A P1&2E event at CMR is linked to active slow-moving weather systems linked to tropospheric Rossby waves triggered by upper-level tropospheric mass divergence anomalies in low latitudes. The source and trajectory these Rossby waves are different through ENSO phases. We have found that heavy precipitation over subtropical eastern Argentina during Niño precede 10 to 8 days. Daily P1&2E events contribute substantially to the mean precipitation total from April to June. The differential influence of the ENSO phases through the seasons of year is evident in such a contribution.

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