The role of the dynamic ocean-atmosphere interactions in the tropical seasonal cycle

Abstract

The role of dynamic ocean-atmosphere interactions on the evolution of the tropical seasonal cycle is explored using a simple coupled model. It is shown that the seasonal cycle in the coupled system can be divided into two parts - a forced part that is a direct response to seasonal changes in the solar radiation and a coupled part that involves dynamic feedbacks between the oceans and atmosphere. The latter part contributes significantly to the pronounced annual cycle in the eastern equatorial Pacific, but is less influential in the western Pacific, owing to the different climate mean conditions. The study further suggests that the ocean-atmosphere interactions in the meridional and zonal direction play different roles in the evolution of the tropical annual cycle. The former is crucial to the development of the strong annual cycle in the near-coastal zone of the eastern Pacific (eastward of 100°W), whereas the latter is instrumental in the westward expansion of the annual cycle along the equator. The results of this study suggest that many important features of the tropical seasonal cycle can be modeled with a relatively simple coupled model, provided that the climate mean conditions are correctly established.