Atmospheric circulation variations and the occurrence of extended wet and dry spells over Southern Africa

Abstract

Abstract Variations in rainfall over southern Africa are explained in terms of variations in pressure and circulation patterns. The extended wet spells of the quasi 18‐year oscillation in rainfall that have affected the subcontinent are shown to have occurred in association with increased pressures in the region where the subtropical ridge of the first zonal standing wave in the 500‐mb surface has its expression in the southern hemisphere, in association with the eastwards displacement or weakening of the Indian Ocean high and a probable lowering of pressure over the subcontinental interior. It is further suggested that the 10‐11 year rainfall oscillation of the southern Cape may be forced by longitudinal changes in the position of the first ridge of standing wave 3 which may oscillate with a similar quasi‐periodicity.