DYNAMICS OVER TROPICAL AFRICA AND ATLANTIC HURRICANES

A scheme has been developed to study tropical tropospheric dynamics with special emphasis on the African continent. In the scheme, a linearised inviscid form of the hydrodynamical equations is solved under different atmospheric static stabilities. The equations are solved with a two-layer model of the atmosphere in order to correctly simulate tropospheric conditions in most parts of tropical Africa. Results show that some modes of the wave-like disturbances generated along the surface of discontinuity between tropospheric air masses propagate and amplify with time. In the case of West and Central Africa, this instability is found to be most-pronounced when the surface of discontinuity between the South-westerlies and the North-easterlies is at 700 hpa level. For East and Southern Africa, a solution was obtained for a wave-like disturbance which has a phase speed of 6.0 ms-1 in the East-West direction, a wavelength of 2000 km, a period of 3.49 days and growth rate of 3.6 per hour, when the interface between the North-East monsoon and the South-East trade winds is at 500 hpa. Further, it is shown that in West and Central Africa, the zone of these unstable waves shifts depending on the sea-surface temperature(SST) anomalies in the Pacific, South Atlantic and Indian Oceans. This shift is shown to have bearing on the frequency of Atlantic hurricanes.