The effect of a tropical sea surface temperature anomaly in a Coupled Ocean-Atmosphere Model

A tropical sea surface temperature (SST) anomaly is imposed as an initial condition in a coupled mixed layer ocean-atmosphere model of the Southern Hemisphere, which is integrated for 80 days. The atmospheric response to the anomaly is shown to be similar to that occurring in an atmospheric model with a fixed SST anomaly, reflecting the persistent nature of tropical SST anomalies. However, in the equatorial region of the coupled model, the anomalous zonal wind circulation produced by the SST anomaly results in enhanced wind mixing, surface heat loss and upwelling on the eastern edge of the anomaly, and reduced wind mixing and surface heat loss on the western edge of the anomaly. This causes an increased SST on the western edge and a decreased SST on the eastern edge, which lead to a westward movement of the anomaly of 20° longitude in 80 days. At extratropical latitudes the changes in the circulation of the atmosphere as a result of the initial anomaly are shown to produce new SST anomalies of up to 2°C. Correlations between the atmospheric forcing and the SST anomalies reveal that wind mixing is a major cause of the anomalies, while the correlation with surface heat flux is small.