Interannual rainfall variability over South America and the South Atlantic

The South Atlantic Convergence Zone (SACZ) is one of the most significant features of the circulation in the Southern Hemisphere. Whilst previous work has focused on the mean state of the SACZ and variability at intra-seasonal scales there has been less attention given to interannual variability. Here we utilise EOF analysis of recent satellite-derived rainfall products to identify objectively patterns of interannual variability during the austral summer months, over South America and the adjacent Atlantic Ocean. The leading mode of variability in November-March is represented by a rainfall tripole, with loadings organised into 3 bands. Enhanced (suppressed) rainfall over eastern Brazil and the SACZ is associated with suppressed (enhanced) rainfall over both the subtropical plains of South America (and the adjacent Atlantic ocean) and the ITCZ over the equatorial Atlantic and South America.

Links between this leading mode of interannual variability and atmospheric circulation are assessed using NCEP re-analysis data. We identify distinct patterns of sea surface temperature anomalies and moisture flux associated with each phase of the EOF loading pattern.