SUMMER CIRCULATION PATTERNS RELATED TO THE UPPER-TROPOSPHERIC VORTICES OVER THE TROPICAL SOUTH ATLANTIC

Daily 200-hPa relative vorticity data have been used to study the domi nant patterns related to the cyclonic vortices over the South Atlantic Ocean in the vicinities of northeast Brazil, during the 1980-1989 per iod. Reference modes were obtained through empirical orthogonal functi on (EOF) analysis of the 200-hPa filtered vorticity anomalies over nor theast Brazil, considering all the southern hemisphere (SH) summers wi thin the study period. The amplitude time series of the first referenc e mode, separately for each SH summer, was correlated with the corresp onding filtered vorticity anomalies in a larger area extending from 20 degrees N to 40 degrees S and between 120 degrees W and 20 degrees W. The correlation patterns feature a wave-like structure along eastern South America, with three main centers: the first one, over the South Atlantic off the northeast Brazil coast, is associated with the cyclon ic vortices; the second one, over eastern Brazil, represents the corre sponding anomalously amplified ridges; and the third one, over souther n Brazil/Uruguay, is related to the equatorward incursions of midlatit ude upper level troughs. This wave-like pattern is consistent with the vortex formation mechanism suggested in previous works. Another wave- like pattern southwest-northeast oriented is evident over the tropical southeastern Pacific, for some years. The interannual variability of these patterns is discussed in this paper.