ATMOSPHERIC BOUNDARY-LAYER FLUXES AND STRUCTURE ACROSS A LAND-SEA TRANSITION ZONE IN SOUTH-EASTERN AFRICA

The structure of the lower atmospheric boundary layer along the southe astern escarpment of Africa during November 1993 is investigated. The study region falls in a transition zone between dry desert to the west and sub-humid vegetated areas bordering the Agulhas Current to the ea st. The physical environment is described by in situ observations from aircraft and a coastal weather station; from satellite composites of sea surface temperature, vegetation reflectance and cloud temperatures ; and synoptic weather data. Example aircraft sections illustrate shar p spatial gradients and changes in surface heat fluxes of order 100 W m(-2) (10 km)(-1). Inland penetration of moisture depends on backgroun d zonal winds and depth of the marine layer. Aircraft turbulent covari ance estimates are used to identify high surface heat fluxes over the inland Karoo desert. During easterly winds, moisture fluxes are greate st over vegetated coastal mountains in a plume 2 km deep. Surface mois ture fluxes over the Agulhas Current and coastal mountains are double those over the cold inshore waters and inland desert. The injection of moist unstable air increases the convective potential during ridging anticyclone weather conditions.