A STUDY OF CIRCULATION CHARACTERISTICS AND INDEX OF SOUTH CHINA SEA SUMMER MONSOON^*

Based on height and wind data of NCEP/NCAR and OLR data,patterns of upper air circulation from April to October have been analyzed,and the South China Sea (SCS) Summer Monsoon Onset (SMO) and retreat have been defined.The empirical formula fitting to the onset index of the SCS SMO has been established,and the onset and ending time of monsoon,together with the intensity index sequence during 1953-1999 are given by the analysis of characteristics of thermodynamic and dynamic factors during the process of SMO.The emergence and development of symmetric vortex pair at both sides of the equator in tropical East Indian Ocean,which may excite the SCS SMO,can be taken as a short-term prediction indicator of SMO.