SST Hindcast with a Coupled GCM Forced by Observed Wind Stress

Ocean GCMs forced by observed surface atmospheric variability are widely used to simulate and study interannual to decadal variations in the ocean, including sea surface temperature (SST) and currents. While observed air temperature and humidity are often prescribed for a realistic simulation, the implied atmospheric thermodynamic forcing of the ocean is flawed physically. To overcome this problem, we force a coupled GCM with observed wind stress but let the atmospheric model to respond to and interact with the simulated ocean variability. The hindcast skills are high in equatorial oceans as represented by correlations with observations for SST and sea surface height. The cross-correlation with observations is low, by contrast, in eastern subtropical oceans of background trade winds, where meridional modes are thermodynamically excited by stochastic extratropical variability and amplified by WES/low cloud feedback. The Pacific meridional modes propagate west-equatorward and modulate ENSO variability, but low correlation with observations suggests that the meridional modes are not forced by ENSO. Other useful applications of the coupled GCM forced by observed wind stress include biases in the mean state and multi-decadal change of tropical climate.