Equatorial Africa is one of the most important convective centers in the tropical regions. Maximum convection and the major rainfall seasons over this region are boreal spring (March-May) and autumn (September-November).

Focused on the spring season, we show that strong quasi-periodic 5-6 day perturbations related to convectively coupled Kelvin waves obviously dominate the intraseasonal variability over equatorial Africa. Using a composite technique as well as the Wheeler and Kiladis (1999) filtering technique, we also show that such a dominance of a Kelvin wave is a unique feature of equatorial Africa for the whole equatorial zone.

The mesoscale convective systems embedded into these synoptic perturbations are studied using high resolution brightness temperature. The diurnal and the wave modulations of the occurrence, the size and the life cycle of the mesoscale convective systems have been studied. These systems are generated mostly over highland specialy those located east of equatorial Africa. They propagate westward over the Congo Basin where they reach their maximum size. The Kelvin wave does not modify significantly the diurnal triggering of convection but favors the development and the maintenance of large organized convection over the Congo Basin. The Kelvin wave thus perturbs mainly the lifetime and the size of the largest convective systems. This gives persisting convection even for hours when it is usually expected to be suppressed (i.e. around noon L.T.).

The equatorial position of the ITCZ over the Atlantic Ocean and over central Africa probably favors the development and the propagation of these coupled equatorial Kelvin waves compared to other tropical regions where the ITCZ is in general off the Equator. Continental surface processes and topography may also play a role in such a strong Kelvin wave disturbance over the Congo Basin.