Using an Ocean Model to Examine ENSO Dynamics

Abstract

Abstract An equatorial ocean model with the Kelvin and first six Rossby waves and n vertical modes is developed to simulate the equatorial sea surface temperature anomalies (SSTAs) and, more importantly, zonal movement of the western equatorial Pacific warm pool associated with an ENSO episode. When forced by observed wind stress, the model reproduces well the SSTAs in both the central and eastern equatorial Pacific. The two gravest baroclinic modes are needed to model the equatorial thermocline depth, zonal current, and SSTAs. The SSTA near the equatorial South American coast is mostly due to upwelling and that in the eastern Pacific from about 150°–100°W is mainly due to both zonal advection and upwelling. The SSTA in the equatorial Pacific near the edge of the warm pool (160°E–160°W) mostly results from the advection of mean SST by the anomalous zonal current and Newtonian damping. Model calculations show that the growing ENSO disturbance, which propagates eastward from the western equatorial Pacific d...