Modeling climate variability in the tropical Atlantic atmosphere

Abstract

Climate variability in the tropical Atlantic sector as represented in six atmospheric general circulation models is examined. On the annual mean, most simulations overestimate wind stress away from the equator although much of the variability can be accounted for by differences in drag formulations. Most models produce excessive latent heat flux as a consequence of errors in boundary layer humidity. Systematic errors are also evident in precipitation and surface wind divergence fields. The seasonal cycle of the zonal trade winds is stronger than observed in most simulations, while the meridional component is well represented. Next interannual variability is considered, focusing on two tropical patterns (Atlantic Niño and interhemispheric modes). The directions of the surface wind anomalies in the models are found to be generally similar to observations, although the magnitude of the wind stress response varies greatly among models. However, all models fail to reproduce the wind-latent heat feedback believed to be essential to interannual variability in this basin.