INTENSITY INDEX OF SOUTH CHINA SEA MONSOON AND ITS VARIATION CHARACTERISTICS

According to the basic characteristics of the activities of summer monsoon in the South China Sea, a standardized index, sI, has been designed that integrates a dynamic factor (southwesterly component) and a thermodynamic factor (OLR) for the indication of summer monsoon in the South China Sea. With the index determined for individual months of June, July and August and the entire summertime from 1975 to 1999, specific months and years are indicated that are either strong or weak in monsoon intensity. The variation is studied for the patterns and sI抯 relationship is revealed with the onset of summer monsoon and the precipitation in Guangdong province and China. The results show that there are quasi-10 and quasi-3-4 year cycles in the interannual variation of the monsoon over the past 25 years. When it has an early (late) onset, the summer monsoon is usually strong (weak). In the strong (weak) monsoon years, precipitation tends to be more (less) in the first raining season of the year but normal or less (normal) in the second, in the province, but it would be more (less) in northeastern China and most parts of the northern China and south of the lower reaches of the Changjiang River and less (more) in the middle and lower reaches of the river, western part of northern China and western China.