Physical Processes Associated with the Tropical Atlantic SST Gradient during the Anomalous Evolution in the Southeastern Ocean

Abstract

This work is focused on the evolution of the dominant air–sea coupled mode in the equatorial and southeastern tropical Atlantic and the associated physical processes. It is shown that in June–August (JJA) the evolution of the dominant mode is mainly dynamically driven and displays a coherent warming or cooling pattern extending from the Angola coast toward the equator in the Gulf of Guinea. For anomalies peaking in JJA, the warming (cooling) is initiated near the Angola coast in March–May. It is suggested that SST anomalies along the coast and near the equator are physically connected. The air–sea interaction along the coast may be a major factor in triggering the development of SST anomalies near the equator, which is intensified by local positive feedbacks that may include Bjerknes and Ekman processes. In return, the warming or cooling near the equator weaken the SST anomalies along the coast by changing the direction of anomalous wind. Slow westward Rossby wave propagation may also play a role in stimulating the equatorial feedback. The thermodynamic processes affect the evolution of this mode. On average, the net surface latent heat flux anomalies are the leading damping factor, and the net surface sensible heat flux plays the same role on a smaller scale, while the net surface shortwave (longwave) radiation heating has a negative (positive) contribution to the SST variation. However, although on average the surface heat flux damps the SST anomalies, the role played by the heat flux varies with regions and components. Spatially, the latent and sensible heat flux as well as the longwave radiation damp air–sea coupling in the eastern South Atlantic near the Gulf of Guinea and amplify the coupling in the western equatorial ocean. The situation is opposite for the solar radiation.