A Model of Tropical Ocean-Atmosphere Interaction

Abstract

A model is used to study ocean-atmosphere interaction in the tropics. The model ocean consists of the single baroclinic mode of a two-layer ocean. Thermodynamics in the upper layer is highly parameterized. If the interface is sufficiently shallow (deep), sea surface temperature is cool (warm). The model atmosphere consists of two wind states that interact with the ocean according to the ideas of Bjerknes. When the eastern ocean is cool, the trade winds expand equatorward in the central Pacific, simulating an enhanced Walker circulation (WC). When the eastern ocean is warm, the trade winds expand eastward, simulating an enhanced Walker circulation (WC) there. For reasonable choices of parameters, the model oscillates at all time scales associated with the Southern Oscillation. The WC has positive feedback with the ocean. This interaction generates persistence, and thereby makes it possible for solutions to oscillate at long time scales. Interaction of the HC with the ocean prevents the model from ever reaching, an equilibrium state. Wind curl associated with the HC generates a Rossby wave in the subtropics. It is the travel time of this wave across the basin that sets the oscillation period of the model.