Index‐ and model‐dependent projections of East Asian summer monsoon in Coupled Model Intercomparison Project Phase 6 simulations

Abstract

AbstractIn terms of five categories of East Asian summer monsoon (EASM) indices and one classic meridional wind index, we project the EASM intensity change over the 21st century using 27 global climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) under the mid‐range combined scenarios of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP2‐4.5). Results show that future changes in the EASM intensity are index‐ and model‐dependent. Relative to the reference period 1985–2014, the EASM intensity strengthens slightly based on the east–west thermal contrast indices but varies little as a whole based on the southwest monsoon indices over the 21st century, with large discrepancies among the models. However, it tends to weaken over time based on the other three categories of indices, including the north–south thermal contrast indices, the shear vorticity indices, and the South China Sea monsoon indices. In terms of the meridional wind index that directly measures the EASM circulation in the lower troposphere and holds valid under future global warming, the EASM intensity strengthens significantly over the 21st century as a consequence of increases in zonal and meridional land–sea thermal contrasts between the East Asian continent and the adjacent oceans of western North Pacific and South China Sea. There are certain relationships between the trends of the meridional wind index and other EASM indices. The projections are overall consistent between the ensemble means of all available 27 models and the 14 good models as selected according to their abilities to simulate the present EASM climatology, but with different magnitudes.