Analysis of a General Circulation Model Simulation of the Atmospheric Response to the Observed Sea Surface Temperature Anomalies of January and February 1983

Abstract

An ensemble of three sets of simulations is produced with the GLA (Goddard Laboratory for Atmospheres) GCM to assess the effect of the El Niño event of 1982?83 on winter climate. The three sets of runs are started from the analyzed initial states of the atmosphere for the 14, 15, and 16 December 1982, respectively, and are integrated through the end of February 1983. Each set consists of a control run, which was forced with climatological SSTs, and a corresponding anomaly run, which was forced with the observed SSTs. The ensemble mean of the model-simulated atmospheric circulation and rainfall anomalies is compared with the corresponding analyses of observations. Most of the observed circulation anomaly features in the tropics are simulated rather well by the model. The tropical sea level pressure anomalies show a typical ENSO pattern: 850 mb wind anomalies show westerly winds over the equatorial Pacific Ocean; 200 mb anomalous winds show anticyclonic vortices straddling the equator; and the 200 mb height anomalies agree well with the corresponding observations. The regions of statistically significant anomaly patterns in the tropics are also in good agreement with observations. The model simulated rainfall anomalies also compare well with the rainfall analysis based on satellite-derived water vapor in the atmosphere from 37 GHz SMMR data. The model's OLR anomaly patterns show close correspondence with the anomalies in satellite observations of OLR. However, there is about a 5?10 degree eastward shift in the major simulated anomalies. This shift is also evident directly over the warm water of the equatorial eastern Pacific, with an even larger shift in the associated patterns in the extratropics. This discrepancy in the simulations leads to some very poor anomaly correlations in the extratropics.