An initial multi-year integration showed significant climate drift in the tropical Pacific sea surface temperatures. Several modifications were made in the coupled model to reduce these errors. Changes were made to the atmospheric model cloudiness parameterizations that improved the simulation of the time mean sea surface temperature. Large errors in the wind direction near the western coast of South America resulted in large mean SST errors in that region. A procedure to reduce these errors was devised and implemented.
Results from the last 17 years of a 62 year simulation are described. The model produces a reasonably realistic seasonal cycle of equatorial Pacific sea surface temperature. However, the upper ocean thermal structure has serious errors. Interannual variability for tropical Pacific sea surface temperatures, precipitation, and sea level pressure that resemble the observed El Ni¤o Southern Oscillation in structure and evolution is found. However, differences from observed behavior are also evident. The mechanism responsible for the interannual variability appears to be related to the delayed oscillator mechanism that occurs in the real climate system.
The structure of precipitation, sea level pressure, and geopotential anomalies associated with the tropical Pacific sea surface temperature interannual variability is isolated and described. The coupled model is capable of producing structures that are similar to those observed. The main conclusion is that the current class of atmosphere-ocean general circulation models are beginning to capture some of the observed characteristics of the climatology of the tropical Pacific and the El Ni¤o Southern Oscillation. The primary obstacles to realistic simulations are ocean model errors in the eastern equatorial Pacific and inadequate meridional resolution in the atmospheric model equatorial Pacific.
last update: 25 July 1995
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