| description abstract | The atmospheric circulation features associated with rainfall variability during the main rainy period of the region of southern Northeast Brazil (sNEB) are determined through principal components analysis and cluster analysis. Daily rainfall, NCEP reanalysis, and OLR data are used from 1979 to 1997. The analyses are performed considering a large area including South America and the Pacific and Atlantic Oceans and also considering a regional area over tropical South America. The influence of synoptic systems, as well as the phenomena associated with their variability, such as El Niño?Southern Oscillation (ENSO) and baroclinic waves over the Pacific Ocean and South America are discussed. Positive (negative) rainfall anomalies over sNEB are related to cold (warm) episodes in the tropical Pacific. On the intraseasonal timescale there are interrelationships among the South Atlantic convergence zone (SACZ), Bolivian high, and the northeast upper-cyclonic vortex. It is noted that rainy periods in sNEB are associated with a northward displacement of the SACZ, an upper-level cyclonic vortex situated over the Atlantic Ocean, intense convection over the eastern Amazon, and an eastward shift in the position of the Bolivian high. At low levels the flow is directed from the Amazon toward the sNEB and there is a shift of the South Atlantic subtropical anticyclone eastward with a weakening of the southeast trade winds over the northeast coast. The dry pattern is associated with a southward displacement of the SACZ, an upper-level cyclonic vortex either close to or over the continent, and a westward displacement of the Bolivian high. In this case, the low-level flow is directed from the Amazon to the south and there is a strengthening and/or westward shift of the South Atlantic anticyclone with an intensification of the southeast trade winds along the northeast coast. | |
