Numerical simulation of SSTA effect on interdecadal variation of East Asian summer monsoon

The effects of regional SST(sea surface temperature) anomaly on interdecadal variation of East Asian summer monsoon(EASM) are investigated based on the observed monthly SSTs in different sea waters(global,extra-tropical,tropical,tropical Indian Ocean-Pacific,tropical Indian Ocean,and tropical Pacific) during 1950—2000.The observed SSTs are used to drive the NCAR CAM3 global atmospheric circulation model in a separate way,followed by long-term multiple group integrations in comparison to ERA-40 and NCEP/NCAR reanalysis data.Numerical simulations show that the SST changes of global,tropical,tropical Indian Ocean-Pacific,and tropical Pacific exert important impacts upon the interdecadal variability of EASM,reproducing the observed interdecadal weakening happened in the mid-late 1970s.Their simulated summer circulation anomalies in the strong and weak EASM years differ greatly,in better agreement with observations.Tropical Pacific is the key region to impact the interdecadal variation of EASM.Extra-tropical SSTA has weaker effect on the interdecadal variation of EASM.The tropical Indian SST-driven simulations reveal an interdecadal strengthening of EASM since the mid-late 1970s opposed to the impact of tropical Pacific SSTA,i.e.,the EASM interdecadal strengthening(weakening) is responded to the interdecadal warm(cold) SSTA in the tropical Indian Ocean.As a background,the interdecadal variation of SST in tropical Pacific has important effect upon the interdecadal weakening of EASM in the mid-late of 1970s.