Influência do Oceano Atlântico Sul na precipitação do Brasil com ênfase sobre o Rio Grande do Sul.

Abstract

In order to analyze the South Atlantic Ocean influence over rainfall patterns in Brazil, in particular, the impacts on the state of Rio Grande do Sul, an oscillation index for the South Atlantic ocean, named IAS, was determined for the period from 1900 to 2008. For this purpose, precipitation rate (Pt), outgoing long wave radiation (OLR) and sea level pressure (SLP) data from the Reanalysis NCEP/NCAR were used. Furthermore, time series of UDEL precipitation and weather stations in Rio Grande do Sul, obtained from the 8th District of Meteorology (Porto Alegre), National Institute of Meteorology (INMET) and the State Foundation for Agricultural Research (FEPAGRO) were also used. A series of IAS was correlated with PDO, SOI, and MEI. The IAS correlation coefficients with PDO and MEI were high, showing that PDO and MEI explain 34% and 28% of the IAS variance, respectively. Rainfall observed in Rio Grande do Sul, and UDEL rainfall, were also correlated with Pt, OLR, SLP. For these variables, the correlation coefficients were more significant in Rio Grande do Sul, mainly for Pt with values around 0.6 for the period 1948-2008 and the cold PDO phase, showing greater degrees of association within this phase of the IAS. Furthermore, correlations were done with the index in 0-5 months advance with the variables Pt, OLR and SLP, the best results were found with up to five months in anticipation of Rio Grande do Sul, mainly. Although correlation does not imply a cause-effect relation ship, these results indicate that rainfall in some regions of Brazil was related to IAS, suggesting that this index is potential predictor of precipitation, considering each phase of the PDO, respectively. In particular, it is suggested that the IAS developed here, is used as a predictor of quality of the rainy season in Rio Grande do Sul, with five months in advance, at least.