Numerical experiments for the influences of sst anomalies over the south china sea-eastern tropical indian ocean on the south china sea summer monsoon onset

Numerical experiments with a low resolution atmospheric general circulation model (AGCM) were conducted to investigate the influences of SST anomalies (SSTA) over the South China Sea- tropical eastern indian Ocean (SCS-TEIO) on the onset of the South China Sea summer Monsoon (SCSM).With positive SSTA over the SCS-TEIO, the anomalous cyclones appear over both sides of the equator at low layer, which weakens the Somali and Australian cross-equatorial SW flow. The anomalous anticyclone in the east of Phillips strengthens the subtropical high with its ridge southwestward shifted.The anomalous anticyclones over both sides of equator at high layer strengthen the South Asia high, thus weaken the SCSM and delay its onset.With negative SSTA over the SCS-ETIO, the anomalous anticyclones appear over both sides of the equator at low layer, which strengthen the Australian but weaken the Somali cross-equatorial SW flow.The anomalous cyclone in northeast of Phillips will weaken the subtropical high.The stronger monsoon meridional circulation over the tropical western Pacific will strengthen the cross-equatorial southerly flow, and the anomalous cyclones over both sides of equator at high layer will weaken the South Asia high, hence strengthen the SCSM and advance its onset.