REGIONAL TELECONNECTION PATTERNS ASSOCIATED WITH SUMMER RAINFALL OVERSOUTH-AFRICA, NAMIBIA AND ZIMBABWE

Climatic determinants of southern African summer rainfall are analysed using statistical techniques. Summer rainfall time series are formula ted for South Africa, Namibia and Zimbabwe areas and correlated with g lobal indices and with field variables: sea-surface temperature (SST), outgoing longwave radiation (OLR), and tropospheric winds at 200 and 700 hPa levels. Linear regression correlations are performed using mon thly standardized departures at various lags before and during the sum mer season. The SSTs in the central equatorial Indian Ocean (CEI) are identified as significant predictors/modulators of southern African ra infall. The SSTs at the CEI are best correlated with South Africa rain fall at r < -0.6 at lags -2 and 0 months and are associated with the E l Nino. The SSTs of the CEI modulate the overlying monsoon trough, as indicated by the OLR correlation maps. A centre of convective action a lternates between southern Africa and the south-west Indian Ocean from year-to-year. A useful circulation index that emerges in the statisti cal analysis is spring-time zonal upper wind anomalies over the equato rial central Atlantic. This index is correlated with South Africa rain fall at r < -0.8 at lags -4 and -2 months. Westerly (easterly) 200 hPa anomalies in spring are followed by a summer of below (above) normal rainfall. Other patterns that have a bearing on summer rainfall includ e a circulation gyre identified in 700 hPa wind correlations off the c oast of south-east Africa. This circulation feature controls the flux of moisture between southern Africa and the northern Mozambique Channe l. The correlation patterns offer statistical guidance in long-range f orecasts and insights to climatic processes that govern the interannua l variability of summer rainfall over southern Africa.