Interhemispheric propagation of seasonal sea surface temperature fluctuations over the western Pacific in CMIP6

Interannual sea surface temperature (SST) variability in the western Pacific is a critical research topic in climate change, as it can significantly impact regional and global weather patterns. Previous observational studies have shown that SST in the southwestern Pacific (SWP) can effectively serve as a precursor signal for SST in the western tropical Pacific (WTP). In this study, we evaluate and compare the modelling capabilities of 32 CMIP6 models to simulate the relationship between SWP and WTP SST. The results indicate that while some CMIP6 models can simulate the spatial connection and physical processes between the SWP and WTP, there are significant intermodel differences. Specifically, the models that best simulate the cross-equatorial propagation of SWP SST anomalies are those that accurately simulate the cross-equatorial wind anomalies induced by SWP SST anomalies, highlighting the key role of wind-evaporation-SST feedback in SST propagation. Further analysis reveals that the intermodel spread in cross-equatorial SST propagation is attributable to model biases in simulating climatological SST and wind speed. Models with warm climatological equatorial SST and strong wind speeds provide favourable conditions for the cross-equatorial propagation of SWP-related SST anomalies towards the north. Warm SST and strong inter-season wind speeds near the equator facilitate the northward propagation of the SWP warm signal, leading to increased warming in the WTP.