Influence of sea surface temperature in the southern Indian and Atlantic Oceans on austral summer rainfall in southern Tanzania

Abstract

As one of the prominent oceanic regions exhibiting high interannual variability of sea surface temperature (SST), the southern Indian and Atlantic Oceans have been found to exert strong impacts on January–February-March (JFM) rainfall in southern Tanzania. The JFM rainfall is found to be significantly linked to the subtropical Indian Ocean Dipole (SIOD)-like SST pattern over the southern Indian Ocean and southern Atlantic Ocean Tripole (SAOT)-like SST structure over the southern Atlantic Ocean. This relationship is linearly independent of the effects of El Niño–Southern Oscillation and the Indian Ocean dipole. The presence of a weakened Mascarene high associated with the negative SIOD phase leads to southerly wind anomalies across the Mozambique Channel, which enhances moisture transport into southern Tanzania and rainfall over the region. The SAOT, on the other hand, excites a zonal elongated wave train-like pattern that induces large-scale cyclonic circulation over the southern Indian Ocean. Subsequently, the western flank of the cyclonic circulation excites southerly wind anomalies traversing through the Mozambique Channel towards the study region, leading to rainfall over the study region. Moreover, the observed wave train-like pattern is echoed in the upper levels, but the anticyclonic center over southern Australia expands further towards northern Madagascar. At this position, the associated anticyclonic wind anomalies reach southern Tanzania to create a divergence condition, enhancing rainfall conditions. Finally, the joint SIOD and SAOT indices show enhanced contribution to the rainfall, explaining about 28% of rainfall variability.