The Seasonal Evolution of the Atmospheric Circulation over West Africa and Equatorial Africa

Abstract

Abstract This paper examines the mean annual cycle of rainfall and general circulation features over West Africa and central Africa for 1958–97. Rainfall is examined using a 1400-station archive compiled by the first author. Other circulation features are examined using the NCEP–NCAR reanalysis dataset. Important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations. In addition to the well-known African easterly jet (AEJ) of the Northern Hemisphere, the seasonal evolution of its Southern Hemisphere counterpart is also described. Thermal wind calculations show that although the southern jet is weaker, its existence is also due to a local reversal of the surface temperature gradient. In the upper troposphere, a strong semiannual cycle is shown in the 200-mb easterlies and a feature like the tropical easterly jet (TEJ) is evident south of the equator in January and February. The paper describes the movement of the rainbelt ...