Revista Brasileira de 'Meteorologia; 1986; Vol. 1, 1 1 - 17 A STUDY OF THE INFLUENCE OF EXTRA-TROPICAL LATITUDES SYSTEMS ON THE CLIMATIC VARIABILITY ON NORTHEAST BRAZIL J. BUCHMANN Departamento de Mereorologia - UFRJ - 22910 - Rio de Janeiro - RJ., Brazil A.D.MOU RA Insritu to de Pesquisas Espaciais/CNPq - 12200 - S5o Jose dos Campos - SP., Brazil M.H.HIRATA Departamento de Energia Mecânica - COPPE - 22910 - Rio de Janeiro., Brazil ABST RACT This study aims at obtaining a better understanding of the relationship between Northeast Brazil interannual precipitation variability (droughts and f looding events) and the global changes in atmospheric circulation. Particularly. the work of Namias (1972) is further explored by analysing then years of monthly mean upper air data (1968-1977) for the region 48N-48S, 20W-90W. A t 700mb. results show an increase of eddy momentum flux (u'v') in the tropical North Atlantic for a wet year (1974) and a decrease for a dry year (1972). The eddy potential energy flux (v) shows a reversal of slope in the tropical region (about 20s to 10N for these two years. Most of the contribution comes from the longitude band of 20W-50W,which includes Northeast Brazil. The 200mb flow is westerly in most of the cases in the Nort.1 Atlantic sector up to 5N or even to the equator. This conditions favors the coupling between the Northeast Brazil region and the extra- tropics, by allowing the propagation of mid-latitude perturbations into the tropics (Webster and Holton, 1982; Simmons, 1982). On the other hand at 700mb the flow is easterly in most of the tropical North Atlantic, thus raising the hportanse of baroclinicity in this problem. A simple, non-linear, two-layer model similar to that of Mak (1969) is used with realistic forcing in the northern boundary (35N) to intercompare the model results for two extreme cases of drought (year 1972) and flood (year 1974) and to verify conditions for equatorward propagation when baroclinicity is present. 1. INTRODUCTION The interannual variability of precipitation over Northeast Brazil (hereafter called Nordeste) is quite high. The occurrence of recurrent drought cond itions severely affects a population of over 30 million people. This variability seems to be linked to the large-scaleatmospheric circulation anomalies over the globe as has been pointed out by Namias (1972), who associated-ytars with high cyclonic activity at 700mb in the ~ewfoundland-~reenland region with rainy years in Nordeste and the reverse for drought years,. Intense blocking conditions over North America are usually associated with devastating droughts over Nordeste. Recently, Moura and Shukla (1981), extending the work of Hastenrath and Heller (19771, suggested that a possible mechanism associated with the occurrence of severe droughts is the establishment of an anomalous thermally induced direct cell with ascending motion in the North Atlantic (in the ITCZ region, near 10N) and descending motion to the south of the equator over Nordeste and adjacent oceanic region. This anomalous cell arises because of the existence of a dipole type of sea surface temperature anomalies in the Atlantic for years of severe droughts.