Lower-tropospheric cyclonic vortices in northern Africa in summer

Abstract

Using analyses from the ECMWF (European Centre for Medium Range Weather Forecasts) model, we compute the monthly and seasonal mean wind and relative vorticity at 1000 and 850 hPa, for the summers of 1980-1982 and 1985-87 for northern Africa (5°-30°N, 20°W-40°E). The mean streamlines display three very persistent cyclonic vortices, that are steady during the summer at 20°N-5°W, 17.5°N-12.5°E, and 12.5°N-25°E. The central and eastern vortices are probably linked to orography. The western vortex seems to be linked to the surface thermal trough. The western and central vortices are located in the generation region of African waves. These vortices are areas of possible mixing of air masses originating from the two meteorological hemispheres. -Authors