Remote Effects of El Nino and Modoki Events on the Austral Summer Precipitation of Southern Africa

Remote effects modulating the austral summer precipitation over southern Africa during El Nino/El Nino Modoki events are investigated by analyzing the observed events during December-February of the years from 1982/83 to 2010/11. Based on the composite analyses, it is found that southern Africa experiences significantly below normal precipitation during El Nino events compared to El Nino Modoki events. During these latter events, precipitation anomalies are not so significant although southern Africa as a whole receives below normal precipitations. The differences in the spatial distribution of precipitation over southern Africa are seen to be related to the sea surface temperature (SST) anomalies of the equatorial Pacific through atmospheric teleconnections.The low-level (850 hPa) Matsuno-Gill response to anomalously high precipitation over the Pacific during El Nino events results in an anomalous anticyclone extending from the equatorial to the subtropical South Indian Ocean. These anomalous anticyclonic winds weaken the tropical moisture flow into the southern Africa landmass. Rossby wave activity flux analysis of the upper-level (300 hPa) circulation shows an anomalous tropospheric stationary wave from the Pacific propagating toward southern Africa and maintaining an anomalous anticyclone over southern Africa. The anomalous Matsuno-Gill response and the anomalous tropospheric stationary wave response are intense during El Nino events, causing drought over southern Africa. During El Nino Modoki events, these processes are weaker compared to El Nino events.