Mixed Layer and Oceanic Kelvin Wave Response Biases to Equatorial Pacific Westerly Wind Events in CMIP6 Models

This study explores the biases in westerly wind events (WWEs) and their induced oceanic Kelvin waves (OKWs) in seven CMIP6 models from three modeling centers that provide daily thermocline depth output. Among the WWEs and OKWs identified in historical simulations, WWEs are generally weaker than observed for a given OKW response, suggesting that OKWs in models respond too strongly to WWE forcing. The equatorial ocean mixed layers in the models are generally too thin and overly-stratified compared to observations. These biases may help inhibit the turbulence-induced mixed layer deepening and trap the WWE-provided momentum within the ocean surface layers. Thus, they support an exaggerated sea surface height build-up and thermocline deepening in OKW initiation regions, which leads to an overly strong OKW response. These biases may be associated with a too-strong net heat flux between the atmosphere and ocean.