Simulated asymmetric connection of SST in the Tasman Sea with respect to the opposite phases of ENSO in austral summer in CMIP6 models

A prior observational study indicates an asymmetric link between Sea Surface Temperature (SST) in the Tasman Sea and El Niño-Southern Oscillation (ENSO) during austral summer. Specifically, El Niño is associated with a dipolar SST anomaly pattern, featuring warming in the northwest and cooling in the southeast, whereas La Niña corresponds to basin-scale warming. This study employed the experiments of coupled models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to assess ENSO's impact on Tasman Sea SST. While all 15 models capture the observed dipolar SST anomalies (SSTAs) in the Tasman Sea during El Niño years, only 7 models capture the basin-scale warmth in the Tasman Sea during La Niña years. Consequently, the models are bifurcated into two groups: group-one models yield one physically reasonable asymmetric connection as the observational, including the asymmetry of oceanic heat transport, especially the Ekman meridional transport anomalies induced by zonal wind stress driven by the asymmetric atmospheric circulation over the Tasman Sea. However, due to abnormal responses to ENSO and systematic biases in model simulations, including jet and storm track, oceanic heat fluxes, ocean currents, and SST, the group-two models fail to reproduce the asymmetric connection between the Tasman Sea and ENSO. This study not only validates the observational asymmetric connection of SSTAs in Tasman Sea with respect to the two opposite ENSO phases, but also provides evidences and clues to reduce the models’ bias in group-two models.