Diversity of the climatological seasonal march of East Asian summer monsoon rainfall among the CMIP6 models

Abstract

We investigated the reproducibility of the observed seasonal march of the East Asian summer monsoon (EASM) in the climate models participating in Phase 6 of the Coupled Model Inter-comparison Project (CMIP6). Overall, the multi-model ensemble of 24 CMIP6 models captured the major characteristics of the seasonal march of the monsoon, but large intermodel diversity was seen. Most of the models simulated a much weaker pre-summer rainy season over South China in May, with the main rainband shifting north. We paid special attention to the Meiyu season in June and the North China rainy season in July, which varied greatly among individual models. The diversity of the seasonal march of the monsoon from June to July in the CMIP6 models is largely modulated by the simulated evolution of the western North Pacific subtropical high (WNPSH), which is closely tied to the sea surface temperature in both the western North Pacific and tropical Atlantic Ocean. Weaker warming in the western North Pacific and stronger warming in the tropical Atlantic favors strong air-sea interaction and the resultant realistic WNPSH, which brings more water vapor to support abundant rainfall, thus resulting in a more realistic seasonal march of the EASM rainfall in the CMIP6 models.