Interaction of the West African Monsoon Circulation and Eastern Tropical Atlantic SSTs

A previous regional atmospheric modeling study shows that, by modulating the land-ocean pressure gradient and the supply of moisture, the Atlantic Ocean SSTs influence the West African monsoon dynamics. Here, the two way interaction of the monsoon with the Atlantic Ocean SSTs is studied using a coupled regional climate model. The model comprises a PSU/NCAR MM5 based regional atmospheric model coupled with a mixed layer ocean model. In this model, the ocean mixed layer and atmospheric boundary layer interact through momentum and heat transfer. Results of the simulations show that during the monsoon onset, the weakening of the northeasterly surface flow reduces evaporation and Ekman upwelling cooling and contribute to the rapid warming of the region off the Western Coast of Africa. Comparison of results from uncoupled and coupled simulations is presented and the primary mechanisms through which the monsoon interacts with the ocean are identified. The role of these interactions in the monsoon onset and evolution are discussed.