SPATIAL STRUCTURE AND INTERANNUAL VARIABILITY OF SUMMER CONVECTION OVER SOUTHERN AFRICA AND THE SW INDIAN-OCEAN

The spatial structure and interannual variability of convective anomalies over southern Africa and the adjacent tropical SW Indian Ocean during the summer months of January and February were investigated using an area rainfall index in comparison with outgoing long-wave radiation (OLR) anomalies and 700-hPa wind fields. Low-frequency cycles of summer rains were noted and contrasts between heavy summer rains in the mid-1970s and droughts in the early 1980s emphasized. The spatial structure of the OLR anomalies imply widespread areas of ascent (descent) during 1976-1978 (1982-1984) over southern Africa. OLR and the area rainfall index were correlated at a peak value of -0.93 at 24-degrees-S, 25-degrees-E. The OLR-rain correlation pattern was dominated by an ENE-WSW convective dipole, with a +0.82 correlation over the SW Indian Ocean east of Madagascar (24-degrees-S, 55-degrees-E). The 700-hPa wind field-area rainfall correlation structure indicated a two-mode (east or west) position for a subtropical trough-ridge pattern. Opposing interannual trends in circulation and convection over the SW Indian Ocean provide new insights into the climate dynamics of the region and serve to correct and update previous conceptual models of wet and dry summers.