UC Santa Barbara

The dominant mode of coupled variability overthe South Atlantic Ocean is known as ‘‘South AtlanticDipole’’ (SAD) and is characterized by a dipole in seasurface temperature (SST) anomalies with centers over thetropical and the extratropical South Atlantic. Previousstudies have shown that variations in SST related to SADmodulate large-scale patterns of precipitation over theAtlantic Ocean. Here we show that variations in the SouthAtlantic SST are associated with changes in daily precipitationover eastern South America. Rain gauge precipitation,satellite derived sea surface temperature andreanalysis data are used to investigate the variability of thesubtropical and tropical South Atlantic and impacts onprecipitation. SAD phases are assessed by performingSingular value decomposition analysis of sea level pressureand SST anomalies. We show that during neutral El Nin˜oSouthern Oscillation events, SAD plays an important rolein modulating cyclogenesis and the characteristics of theSouth Atlantic Convergence Zone. Positive SST anomaliesover the extratropical South Atlantic (SAD negative phase)are related to increased cyclogenesis near southeast Brazilas well as the migration of extratropical cyclones furthernorth. As a consequence, these systems organize convectionand increase precipitation over eastern South America.