Impact of Desert Environment on the Genesis of African Wave Disturbances

Abstract During summer the meteorological conditions in the lower troposphere between the anticyclonic-shear (north) side and cyclonic-shear side of the midtropospheric easterly jet over North Africa are rather different. A significant dynamical feature on the cyclonic-shear side of the jet core is the reversed potential vorticity gradient, which satisfies the Charney-Stern necessary condition for combined barotropic-baroclinic instability. There is no indication of such combined instability on the anticyclonic-shear side. The desert air to the north is characterized by near-neutral static stability and a marked horizontal temperature gradient as a result of strong surface heating. The role of the unique desert environment in the dynamics and energetics of African wave disturbances is examined based on linearized perturbation analysis. A “dry” (no moist processes) system of primitive equations is used in the analysis. Results reveal that the mean thermal conditions over the east-central African deserts in...