Assessing the Impact of Sea Surface Temperature Biases in CMIP6 Coupled Models on the North Pacific Westerly Jet

Abstract

This study investigates the impact of sea surface temperature (SST) biases on the latitude of the climatological North Pacific westerly jet using multi‐model analyses and atmospheric general circulation model (AGCM) sensitivity experiments. A comparison of atmospheric‐only and coupled simulations from 35 models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) for 1985–2014 reveals a robust southward shift of the jet in the coupled simulations, identified in 34 models. Sensitivity experiments with an AGCM demonstrate that the jet latitude differences between atmospheric‐only and coupled simulations can be reproduced by imposing annual‐mean SST biases. Further analysis shows that the cold SST bias over the western North Pacific subtropical gyre dominates the jet response. Reduced atmospheric baroclinicity associated with weakened meridional temperature gradients suppresses eddy activity, favoring a southward jet shift.