Abstract
Many coupled ocean–atmosphere general circulation models (GCMs) suffer serious biases in the tropical Atlantic including a southward shift of the intertropical convergence zone (ITCZ) in the annual mean, a westerly bias in equatorial surface winds, and a failure to reproduce the eastern equatorial cold tongue in boreal summer. The present study examines an ensemble of coupled GCMs and their uncoupled atmospheric component to identify common sources of error. It is found that the westerly wind bias also exists in the atmospheric GCMs forced with observed sea surface temperature, but only in boreal spring. During this time sea-level pressure is anomalously high (low) in the western (eastern) equatorial Atlantic, which appears to be related to deficient (excessive) precipitation over tropical South America (Africa). In coupled simulations, this westerly bias leads to a deepening of the thermocline in the east, which prevents the equatorial cold tongue from developing in boreal summer. Thus reducing atmospheric model errors during boreal spring may lead to improved coupled simulations of tropical Atlantic climate.
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Acknowledgments
This study was supported by the NOAA CLIVAR Program and the Japan Agency for Marine-Earth Science and Technology through its sponsorship of the International Pacific Research Center. All the model output was downloaded from The IPCC Data Archive at Lawrence Livermore National Laboratory, which is supported by the Office of Science, U.S. Department of Energy. The authors would like to thank Justin Small and two anonymous reviewers for their helpful suggestions. IPRC publication #498.
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Richter, I., Xie, SP. On the origen of equatorial Atlantic biases in coupled general circulation models. Clim Dyn 31, 587–598 (2008). https://doi.org/10.1007/s00382-008-0364-z
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DOI: https://doi.org/10.1007/s00382-008-0364-z