EOF EXPANSION OF SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA

Using the NECP data from 1983 to 1992, the spatial and the temporal variation characteristics of main models of the summer monsoon onset process in the South China Sea(SCS) have been studied by the method of EOF expansion. It has been found that the northward shift of solar radiation is the most important factor of the monsoon onset. There is very evident adjustment of wind field at 850 hPa associated with the Asian summer monsoon onset in typical monsoon area. Amplification of westerlies trough and ridge in Southern Hemisphere mid-high latitude and augmentation of subtropical system meridional circulation in Northern Hemisphere are significant role of the Asian summer monsoon onset. The western Pacific Ocean high pressure abated rapidly and retreated east about 5 days before the monsoon erupts, which caused the southwest monsoon onset.