Abstract
Atmosphere–ocean coupled processes responsible for generating and maintaining the equatorial warm pool were investigated using models of different complexities. The primary focus was to answer the following question: why is the observed warm pool concentrated around the maritime continent? In this first of a two-part series, the solutions of a simple conceptual model that represents the tropical Pacific and Indian Oceans interacting via the Walker circulation are examined. When the interbasin coupling is sufficiently strong, surface wind convergence over the Maritime Continent associated with easterly trades over the Pacific acts to generate the equatorial westerly over the Indian Ocean, leading to a warm pool spontaneously emerging between the two ocean basins. The conceptual model shows that tropical climate has two equilibria, depending upon the ocean basin widths—a single warm pool regime corresponding to the current climate and a split warm pool regime that accompanies warm pools created in the western parts of each ocean basin. The latter is found to be unstable and hence exhibits large-amplitude vacillations between the ocean basins being further amplified by the Bjerknes feedback. The above two regimes of the equatorial warm pool are identified in the model incorporating the interactive Atlantic Ocean as well, wherein the mean state and variability in the three ocean basins qualitatively agree with the observations.
Corresponding author address: M. Watanabe, Center for Climate System Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan. Email: hiro@ccrs.u-tokyo.ac.jp
