The climatology and interannual variability of the East Asian summer monsoon simulated by a weakly coupled data assimilation system

ABSTRACT With the motivation to improve the simulation of the East Asian summer monsoon (EASM) in coupled climate models, oceanic data assimilation (DA) was used in CAS-ESM-C (Chinese Academy of Sciences–Earth System Model–Climate Component) in this study. Observed sea surface temperature was assimilated into CAS-ESM-C. The climatology and interannual variability of the EASM simulated in CAS-ESM-C with DA were compared with a traditional AMIP-type run. Results showed that the climatological spatial pattern and annual cycle of precipitation in the western North Pacific, and the ENSO-related and EASM-related EASM circulation and precipitation, were largely improved. As shown in this study, air–sea coupling is important for EASM simulation. In addition, oceanic DA synchronizes the coupled model with the real world without breaking the air–sea coupling process. These two successful factors make the assimilation experiment a more reasonable experimental design than traditional AMIP-type simulations. Graphical Abstrac