A regional ocean-atmosphere coupled model is developed for climate variability studies. The model allows dynamic and thermodynamic interactions between the atmospheric boundary layer and an ocean mixed layer spatially and temporally varying depth. The model's performance in simulating observed climatological fields over tropical Atlantic and West Africa is evaluated. It is then used to identify the contributions of various land-air-sea interaction mechanisms to the strong seasonal SST variability over the eastern Atlantic Ocean and the influence of this variability on the West African Monsoon circulations. In the model, the observed rapid cooling of the Gulf of Guinea between April and July is primarily due to increased entrainment of cool underlying water and enhanced evaporation associated with the acceleration of the southerly winds driven by the African heat low.

Over the northeastern tropical Atlantic, the seasonal SST rise during this period is mainly associated with radiative heating. The northward migration of the ITCZ low weakens the northeasterly winds. The associated suppression of evaporation and sensible heat transfer significantly contributes to the warming. This seasonal warming of the northeastern tropical Atlantic weakens the easterly anti-cyclonic winds and strengthens the cyclonic westerly monsoon winds associated with the African heat low.