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 southern African rainfall discussed. Sea-surface temperature (SST) is the most important ocean variable for atmospheric circulation and rainfall patterns, and particular emphasis is devoted to understanding ifs behaviour Aspects of the strength and distribution of the subtropical gyre of the South Indian Ocean, particularly the Agulhas system as it relates to SST patterns are also considered. While effects of climate variability, particularly those of rainfall, tend to be most obvious to us on intraseasonal to interannual time scales, patterns on decadal to multidecadal scales are also of interest, not least because of the possibility that they may modulate the shorter scale phenomena. Far reasons 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 interannual, it is suggested that SST variability may be forced largely by atmospheric changes whereas over longer periods, large-scale ocean dynamics may be important for driving SST variability.