SIMULATION OF THE TROPICAL PACIFIC CLIMATE WITH A COUPLED OCEAN-ATMOSPHERE GENERAL-CIRCULATION MODEL .1. THE SEASONAL CYCLE

A multiyear simulation with a coupled ocean-atmosphere general circula tion model (GCM) is presented. The model consists of the UCLA global a tmospheric GCM coupled to the GFDL oceanic GCM; the latter is dynamica lly active over the tropical Pacific, while climatological time-varyin g sea surface temperatures (SST) are prescribed elsewhere. The model s uccessfully simulates the main climatological features associated with the seasonal cycle, including the east-west gradient in SST across th e equatorial Pacific. The most apparent deficiencies include a systema tic cold bias (similar to 2 K) across most of the tropical Pacific and underestimated wind stress magnitudes in the equatorial band. Multich annel singular spectrum analysis is used to describe the multivariate structure of the seasonal cycle at the equator in both the model and o bserved data. The annual harmonic in equatorial SST is primarily wind driven, while air-sea interaction strongly affects the semiannual harm onic.(1)