Influence of Indian ocean sea-surface temperature anomalies on the general circulation of southern Africa

Modelling the effect of sea-surface temperature (SST) anomalies on the rainfall of southern Africa has been a major focus of climate research in the region in recent years. The purpose of this experiment was to find a possible dynamic link between the Indian Ocean SSTs and the general circulation over southern Africa. Anomalous SST fields were constructed by superimposing an anomaly on the climatological SST data. The anomaly was chosen to represent an area in the Indian Ocean that showed the best correlations between Indian Ocean SST anomalies and rainfall over South Africa, as revealed by statistical studies. This field served as a lower boundary condition for the COLA atmospheric general circulation model (AGCM). The model was run to simulate the atmosphere for periods of two months, using initial data for January 1991 and January 1992. These years are good examples of above- and below-average rainfall, respectively, in the summer rainfall areas of southern Africa. Results show that warm SST anomalies in the Indian Ocean cause a drop in surface pressure and enhanced rainfall in the area of the anomaly The general circulation around the SST anomaly is changed in such a way that convective rainfall over the eastern and north-eastern areas of South Africa is suppressed This is more evident during the second month of the the integration, indicating that there is a time lag between the cause and effect of this warm anomaly. Cold SST anomalies show negligible effects on weather conditions over South Africa.