Asymmetric Responses in the Equatorial Pacific to Wind Forcing in OMIP2 Experiments: Role of Zonal Currents

Abstract Numerical experiments from phase II of the Ocean Model Intercomparison Project (OMIP2) generally underestimate the asymmetric temperature response to interannual changes in the wind‐stress over the equatorial western Pacific subsurface. Despite the knowledge that such a bias may be directly behind the general lack of asymmetry in model‐simulated El Niño‐Southern Oscillation (ENSO), its causes remain unknown. Here we report that a weaker response in the zonal currents to wind forcing in these models results in a biased response in the vertical motion which in turn causes weaker asymmetric temperature responses through the contribution of the vertical motion to the advective heating (dynamic heating). This finding underscores the critical importance of accurately modeling the zonal currents—a previously less noticed element in the modeling effort—to better capture the asymmetric responses in the tropical western Pacific to external wind forcing and thereby improving simulations of ENSO by coupled climate models.