南海夏季风强度指数及其变化特征

AN INDEX OF SOUTH CHINA SEA SUMMER MONSOON INTENSITY AND ITS VARIATION CHARACTERS

依据南海夏季风活动的基本特征,设计了一个动力学因子（西南风分量）与热力学因子（OLR）相结合标准化的南海夏季风强度指数Is。并计算出1975～1999年6、7、8各月及夏季Is的数据,给出了强、弱夏季风月和年。分析了其变化特征和Is与夏季风爆发早晚,及与广东和我国降水的关系。结果表明:近25年来,南海夏季风年际变化有准10年和准3～4年变化周期。南海夏季风爆发早（晚）,则该年夏季风大多偏强（弱）。南海夏季风强（弱）年,广东后汛期偏涝（旱）,前汛期降水正常或偏旱（正常）,我国东北、华北大部和江南大部夏季降水偏多（少）,而长江中下游和华北西部以及华西偏少（多）。

According to the basic characteristic of activities of South China Sea summer monsoon, an index of South China Sea summer monsoon intensity, Is, which is composed by both dynamic factor (southwest wind component) and thermodynamic factor (OLR) was studied in this paper. The results of Is of June, July, August from 1975 ~ 1999 have been calculated and the strong and weak monsoon years have been given. The characteristic of Is and the relationship between variations of Is and the date of the summer monsoon onset and the rainfall amount in Guangdong province and China have been analyzed. The results showed: the multi-year variations of the summer monsoon have ten years and 3-4 years periods in past 25 years. The earlier the summer monsoon setups, the stronger the summer monsoon is, and vise verse. In strong summer monsoon year, the rainfall amount in Guangdong is more than normal in the second stage of rain period and is normal or less than normal in the first stage of rain period. And the summer rainfall amount is more than normal in the northeast part of China, in the north part of middle China and south of Yangzi River and is less than normal in the west part of China. They are reverse in weak summer monsoon year.