The Mean Circulation in the Lower Troposphere over Southern Africa

Abstract

Charts showing summer and winter mean streamlines of the wind at 2, 4 and 6 kilometres above sea-level over Southern Africa are presented. These charts are preliminary, being based upon observations published in the form of frequency tables or wind roses only. Charts showing the pressure distribution at sea-level over the surrounding oceans and at 1,250 geopotential metres over the Union, Bechuanaland and South West Africa, are included. It is shown that the anti-cyclonic centre east of Transvaal at 2 kilometres is displaced rapidly to central or northern South West Africa at 4 and 6 kilometres in both seasons, while the high pressure axis is about 4 to 8 degrees nearer the equator in winter. The Intertropical Convergence Zone is indicated at 2 and 4 kilometres in summer, stretching from northern Madagascar westwards to the Zambesi valley. Another zone of convergence between equatorial air from the Congo and tropical air from South Africa stretches from the Zambesi valley in a westerly direction across southern Angola. In winter an almost uninterrupted easterly to south-easterly airstream exists at all levels to the north of the high pressure axis. A col is indicated over the Mozambique Channel or Madagascar in summer and winter. “Constancy indices” have been entered on the maps for the South African area.