Influence of intraseasonal oscillation on east-asian summer monsoon

The impact of intraseasonal oscillation on the onset of summer monsoon in the South China Sea (SCS) region is studied by using NCEP reanalysis data, the SCSMEX data and precipitation data in China.It is shown that the onset of summer monsoon in the South China Sea region is closely related to the activity of intraseasonal oscillation.Particularly, the existence of low frequency cyclone over the east of Philippines and its expanding into the South China Sea play an important role in the onset of the SCS summer monsoon.The analyses of the circulation pattern and summer rainfall showed that the climate variations in China caused by the strong and weak summer monsoons are completely different, even are out of the phase.Analyzing the activity of atmospheric intraseasonal oscillation (ISO), we found that the atmospheric ISO at 850 hPa over the SCS and neighboring regions is strong (weak) corresponding to strong (weak) SCS summer monsoon.The comparison of the atmospheric circulation pattern with the circulation pattern of atmospheric ISO showed that strong and weak East-Asian summer monsoon circulations (200 hPa and 850 hPa) should mainly result from the abnormal activity of atmospheric ISO.