VARIABILITY OF THE SOUTH INDIAN-OCEAN AND IMPLICATIONS FOR SOUTHERN AFRICAN RAINFALL

Variability of the South Indian Ocean on time scales ranging from the intraseasonal to the multidecadal is examined, and implications for so uthern African rainfall discussed. Sea-surface temperature (SST) is th e most important ocean variable for atmospheric circulation and rainfa ll patterns, and particular emphasis is devoted to understanding ifs b ehaviour Aspects of the strength and distribution of the subtropical g yre of the South Indian Ocean, particularly the Agulhas system as it r elates to SST patterns are also considered. While effects of climate v ariability, particularly those of rainfall, tend to be most obvious to us on intraseasonal to interannual time scales, patterns on decadal t o multidecadal scales are also of interest, not least because of the p ossibility that they may modulate the shorter scale phenomena. Far rea sons of geography and ocean circulation processes, it appears that SST in the Agulhas region is particularly sensitive over a range of time scales and to a variety of mechanisms. On time scales up to the intera nnual, it is suggested that SST variability may be forced largely by a tmospheric changes whereas over longer periods, large-scale ocean dyna mics may be important for driving SST variability.