El Niño–La Niña Events Simulated with Cane and Zebiak's Model and Observed with Satellite or In Situ Data. Part I: Model Data Comparison

Abstract

The Zebiak and Cane model is used in its ?uncoupled mode,? meaning that the oceanic model component is driven by the Florida State University (FSU) wind stress anomalies over 1980?93 to simulate sea surface temperature anomalies, and these are derived in the atmospheric model component to generate, wind anomalies. Simulations am compared with data derived from FSU winds, International Satellite Cloud Climatology Project cloud convection, Advanced Very High Resolution Radiometer SST, Geosat sea level, 20°C isotherm depth derived from an expendable bathythermograph, and current velocities estimated from drifters or current-meter moorings. Forced by the simulated SST, the atmospheric model is fairly successful in reproducing the observed westerlies during El Niño events. The model fails to simulate the easterlies during La Niña 1988. The simulated forcing of the atmosphere is in very poor agreement with the heating derived from cloud convection data. Similarly, the model is fairly successful in reproducing the warm anomalies during El Niño events, However, it fails to simulate the observed cold anomalies. Simulated variations of thermocline depth agree reasonably well with observations. The model simulates zonal current anomalies that are reversing at a dominant 9-month frequency. Projecting altimetric observations on Kelvin and Rossby waves provides an estimate of zonal current anomalies, which is consistent with the ones derived from drifters or from current meter moorings. Unlike the simulated ones, the observed zonal current anomalies reverse from eastward during El Niño events to westward during La Niña events. The simulated 9-month oscillations correspond to a resonant mode of the basin. They can be suppressed by cancelling the wave reflection at the boundaries, or they can be attenuated by increasing the friction in the ocean model.