Modeling Tropical Pacific Sea Surface Temperature: 1970–87

Abstract

An attempt is made to model the sea surface temperature (SST) of the tropical Pacific Ocean between January 1970 and August 1987. The SST is computed using the model and heat flux parameterization discribed in the climatological study of Seager et al. The model is forced with the observed winds as given by the Florida State University analysis. The results indicate that while short period variability in the model and observations is largely uncorrelated, variability with periods greater than about one year is well represented in the model. Each El Niño that occurred in this time period is captured by the model. The main discrepancies in the evolution of the 1982/83 and 1986/87 model El Niño events are the inability of the model equatorial SST anomaly to cool in early 1983 and the disappearance of the 1986/87 anomaly during 1987. The results suggest a number of conclusions. In the east Pacific equatorial Kelvin waves, excited by variations in the trade wind strength in the central and west Pacific, increase the SST via depression of the thermocline. In this region the surface heat flux acts as a negative feedback on the SST anomaly. However, in the central Pacific the surface heat flux anomalies are reinforcing heating through suppression of latent heat loss as a result or weakened trades. Zonal advection of warm water from the west, associated with Rossby waves excited by trade wind relaxation, contributes to warming in both the central and west Pacific. Anomalous cooling by entrainment is a negative feedback on the SST anomaly in the central Pacific.