A Model Study of Oceanic Mechanisms Affecting Equatorial Pacific Sea Surface Temperature during the 1997–98 El Niño

Abstract

In this study, the processes affecting sea surface temperature variability over the 1992-98 period, encompassing the very strong 1997-98 El Nin o event, are analyzed. A tropical Pacific Ocean general circulation model, forced by a combination of weekly ERS1-2 and TAO wind stresses, and climatological heat and freshwater fluxes, is first validated against observations. The model reproduces the main features of the tropical Pacific mean state, despite a weaker than observed thermal stratification, a 0.1 m s 1 too strong (weak) South Equatorial Current (North Equatorial Countercurrent), and a slight underestimate of the Equatorial Undercurrent. Good agreement is found between the model dynamic height and TOPEX/Poseidon sea level variability, with correlation/rms differences of 0.80/4.7 cm on average in the 10N-10S band. The model sea surface temperature variability is a bit weak, but reproduces the main features of interannual variability during the 1992-98 period. The model compares well with the TAO current variability at the equator, with correlation/rms differences of 0.81/0.23 m s 1 for surface currents. The model therefore reproduces well the observed interannual variability, with wind stress as the only interannually varying forcing.