The southern oscillation and South African summer rainfall

Abstract

AbstractUsing data since 1882 the relationship between summer rainfall over South Africa and the ENSO phenomenon is investigated. A strong association between Warm Events and dry spells, and between Cold Events and wet spells is discussed. The temporal and spatial variability in the relationship is presented. Rainfall during December and March correlates significantly with the previous winter's SOI but rainfall during the mid‐summer months, January and February, shows much weaker correlation. A significant relationship is detected between the summer rainfall and mean monthly geopotentials as well as the 850–500 hPa thermal wind over the central parts of South Africa. Distinctions are made between the dominant rain‐producing systems with regard to these parameters. During January and February, when the SO/rainfall relationship is fairly weak, rainfall develops in a predominantly quasi‐barotropic circulation. On the other hand, during December and March the most significant SO/rainfall correlation coincides with a shift to baroclinic systems. Analysis suggests that a clear signal of the SO can be observed in the phase and amplitude of summertime synoptic‐scale baroclinic systems over the South African region.