COMPOSITE ANALYSIS OF SUMMER MONSOON ONSET PROCESS OVER SOUTH CHINA SEA

doi:10.3969/j.issn.1004-4965.2001.01.002

Abstract：Based on the method of composite analysis, the onset process ofsummer monsoon over South China Sea (SCS) is investigated. Result indicates that convection activities firstly appear over Indo-China peninsula prior to the onset of the monsoon, then occur around Philippines as the monsoon begins immediately, implying that the convection activities around Philippines serve as one of the reasons leading to the SCS monsoon onset. Before the SCS monsoon onset, the equatorial westerly over the Indian Ocean (75～95°E ) experiences noticeable enhancement and plays an important role on the SCS monsoon onset. On the one hand,it propagates eastward rapidly and causes the establishment and strengthening of equatorial westerly in the southern SCS, on the other hand,it results in the migration southward of the westerly on south side of the south-China stationary front by means of shift northeastward of the westerly and convection over the Bay of Bengal. Further study also shows that the intensification of equatorial westerly in the Indian Ocean (75～95°E) and the southern SCS is closely related to the reinforcement of the southern-hemisphere Mascarene high and Australian high, and cross-equatorial flow northward around Somali, 85 and 105 °E, respectively.