Generation of Convective Storms over the Escarpment of Northeastern South Africa

Abstract

The generation of convective storms over the escarpment of the northeastern region of South Africa is examined in terms of synoptic-, meso-, and local forcing. Severe storm days are defined and contrasted with no-storm days over a 5-year period. Storms are associated with midtropospheric troughs in the westerlies which interact with a major topographic boundary. A mesoscale capping inversion is shown to exist in the lee of the escarpment on storm days. Formation of the inversion is enhanced by a diurnal shift in wind direction across the escarpment. The subsidence inversion anchored to the escarpment is deepened during the day by the advection of the daytime mixed layer off an elevated beat source. Development of severe storms occurs selectively in time and space where easterly low-level moist inflow can penetrate the capping inversion. There appears to be a critical relationship between the larger-scale synoptic circulations and the meso- and local-effects for severe storms to develop.