Surface Heat Balance in the Equatorial Pacific Ocean: Climatology and the Warming Event of 1994–95

The surface heat budget in the equatorial Pacific Ocean was investigated through ocean model simulations, both the climatological cycle and the case of the 1994–95 warm event. The dominant processes governing the seasonal cycle of sea surface temperature (SST) vary significantly across the basin. In the western Pacific the annual cycle of SST is primarily in response to net surface heat flux. In the central basin the magnitude of the zonal advection term is comparable to that of the net surface heat flux. In the eastern basin the role of zonal advection is reduced and the vertical mixing and advection are more important. The model estimate of the vertical mixing contribution to the mixed layer heat budget compared well with estimates obtained by analysis of observations using the same diagnostic vertical mixing scheme. During 1994–95 the largest positive SST anomaly was observed in the midbasin and was related initially to reduced latent heat flux due to weak surface winds and later to anomalous zonal advection. In the eastern Pacific where winds were not significantly anomalous throughout 1994–95, only a moderate warm surface anomaly was detected. This is in contrast to strong El Niño events where the SST anomaly is largest in the eastern basin. Overall, the balances inferred from the model forced by Special Sensor Microwave/Imager winds are consistent with the balances derived using tropical atmosphere–ocean moorings data and Reynolds SST.