Analysis of the heavy precipitations during the summer 1997-1998 in southeastern South America and their relations with the summer 1982-1983

Abstract

In this paper the synoptic situation related to the intense rainfalls observed during summer 1997-1998 under strong El Niño conditions is studied. The mean synoptic situation of the summer 1997-1998 was characterized by a positive anomaly in the Pacific Ocean at 500 and 1000 hPa, approximately located at 55ºS,80ºW, northeast of that corresponding to El Niño event of 1982-1983. This phenomenon of blocking activity, along with a band of negative anomalies between 30 and 40ºS and 120 and 40ºW in 500 hPa and the intensification of the mass flux of air from the Amazonia to the northern limits of the Patagonia were the common characteristics of both cases. Then a comparison is performed between the rainfalls associated to El Niño events corresponding to the summer 1982-1983 and 1997-1998, in the south of South America. In both cases, intense rainfalls producing important flooding events within the Rio de la Plata basin have been recorded. During the first event, the maximum precipitation was observed in Paraguay and Misiones (Argentina), while a much larger area located to the south of the latter extending towards the center of Argentina was affected during the second event.