Evaluation of the zonal wind stress response to SST in the CMIP5 AMIP simulations

Zonal wind stress plays an important role in the evolution of El Nino-Southern Oscillation (ENSO) events; however, a comprehensive comparison and analysis in terms of model performance and related bias in the interannual variability of zonal wind stress across the tropical Pacific has yet to be performed. In this study, the authors evaluate how well the individual atmospheric models participating in phase 5 of the Coupled Model Intercomparison Project simulate zonal wind stress. It is found that the wind stress anomalies simulated by the multi-model ensemble are weaker than those in the observation in both El Nino and La Nina events, with a larger bias in the former. Further analysis indicates that the bias associated with El Nino events may be mainly attributable to the weaker negative precipitation anomalies in the AMIP simulations, compared with observations, over the eastern Indian Ocean. Through the Gill-like responses in atmospheric circulation, the rainfall bias over the eastern Indian Ocean results in an easterly wind stress anomaly in the western and central equatorial Pacific, which to some extent offsets the westerly wind stress anomalies associated with El Nino events. Consequently, the responses of zonal wind stress anomalies to warm SST anomalies are much underestimated in AMIP simulations during El Nino events.