On the Seasonal Cycle of the Equatorial Atlantic Ocean

Although the seasonal cycle of the equatorial Atlantic and Pacific Oceans have many similarities, for example, an annual signal is dominant at the equator even though the sun ‘‘crosses’’ the equator twice a year, different processes determine the seasonal cycles of the two oceans and in the Atlantic different processes are important in the east and west. In the Gulf of Guinea in the eastern equatorial Atlantic, the seasonal cycle of surface winds is primarily in response to seasonal variations in land temperatures so that annual changes in sea surface temperatures are, to a first approximation, the passive response of the ocean to the winds. The seasonal cycle of the western equatorial Atlantic has similarities with that of the equatorial Pacific—both are strongly influenced by ocean–atmosphere interactions in which the surface winds and sea surface temperature patterns depend on each other—but only in the western equatorial Atlantic are the seasonal variations in sea surface temperature influenced by vertical excursions of the thermocline. These results are obtained by means of a general circulation model of the atmosphere and a relatively simple coupled ocean–atmosphere model.