Inter-Model Spread of the Simulated East Asian Summer Monsoon Rainfall and the Associated Atmospheric Circulations From the CMIP6 Models

The model uncertainty, one of the major sources of projection uncertainty, is still a challenge in the climate change projection. In this study, the model uncertainty in simulating the East Asian summer monsoon rainfall and its physical link to the upper-level jet streams and the western North Pacific subtropical high (WNPSH) are investigated from the Coupled Model Inter-comparison Project Phase 6 (CMIP6) models. The results show that extracted by the inter-model Empirical Orthogonal Function method, the leading inter-model mode of the rainfall is characterized as a meridional pattern. The positive mode (a continent-wet-ocean-dry pattern) is closely associated with a northward shift of the oceanic branch of the East Asian subtropical jet and a northward movement of the WNPSH, while the negative mode (a continent-dry-ocean-wet pattern) is highly correlated with an enhanced East Asian polar-front jet combined with a weakened land branch of the East Asian subtropical jet as well as a weakened and eastward recess of the WNPSH. This systematic link among the atmospheric circulations and the leading inter-model mode is maintained by the negative phase of the Victoria Mode in the North Pacific and warming over the Atlantic Ocean in the positive mode, and the cooling over the Indian Ocean, Atlantic Ocean and the warming over the central Pacific in the negative mode. Our findings suggest that the physical linkage between the atmospheric circulations and monsoon rainfall is useful to understand the model uncertainty, which would be helpful in providing potential indicators of the East Asia summer monsoon change.