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. Plain Language Summary: Monsoon rainfall has profound economic and social impacts, however large uncertainties lie in the climate model simulations. In this study, the inter‐model spread is used to extract the model uncertainty for the East Asian summer monsoon rainfall. The leading inter‐model mode is a meridional dipole pattern, which is closely associated with the concurrent variations of jet streams and the intensity and meridional movement of the western North Pacific subtropical high (WNPSH), but with the asymmetric response. The associated jet stream and the WNPSH variations are sustained by the oceanic conditions over the Atlantic Ocean, Pacific Ocean, and Indian Ocean, and therefore results in the inter‐model spread of the monsoon rainfall. Our findings suggest a useful metric to understand the traces of model uncertainties, focused on the physical linkage between the atmospheric circulations and the monsoon rainfall. Key Points: The leading inter‐model spread in East Asian summer monsoon rainfall is a meridional pattern from the Coupled Model Inter‐comparison Project Phase 6 modelsThe associated jet streams and western North Pacific subtropical high (WNPSH) variations exhibit asymmetric responses to this inter‐model spreadThe uncertainties in the north Pacific, Atlantic, and Indian Ocean have physically linked the jet stream and WNPSH variations to this inter‐model spread [ABSTRACT FROM AUTHOR]