1997年东亚夏季风异常活动在汛期降水中的作用

ROLE OF SUMMER MONSOON IN ANOMALOUS PRECIPITATION PATTERNS DURING 1997 FLOODING SEASON

利用 1 997年逐日降水资料和国家气象中心提供的T6 3再分析资料 ,详细讨论了中国汛期降水及东亚夏季风活动的异常特征及其间的联系。结果表明 ,该年中国夏季降水及东亚夏季风活动均表现了突出的异常 ,东部雨带长期滞留在江南、华南一带 ,夏季风向北的推进很弱 ,主要活跃于较低纬度 ,最北仅至 3 5°N ,未能在黄河以北的地区建立 ,比起气候意义下夏季风北进的最高纬度偏南 1 0°左右。在这一过程中 ,夏季风异常是主要雨带异常发展的重要影响因子 ,候大雨带的建立和北推均与季风的建立与活跃密切相关。进一步对大尺度水汽场的分析表明 ,夏季风的活动明显改变了大尺度水汽输送及辐合 ,进而影响和制约了主要雨带的分布。夏季风爆发后 ,南海及中国大陆的主要水汽输送源均发生了明显变化 ,来自于孟加拉湾和热带印度洋的水汽输送到南海后 ,再从南海输送到中国大陆。而季风的活动同时也制约了强水汽辐合带的出现 。

By means of daily precipitation data and T63 reanalyzed data in 1997, the precipitation in China during the flooding season and East Asian summer monsoon activities are studied. The results show that the precipitation in South China was obviously more than that in North China. The eastern rainbelt stayed in the South and to the south of the Yangtz River for a long time. Corresponding to the anomalous precipitation patterns, the monsoon activities showed prominent anomalies. The northward propagation of summer monsoon was very weak. The monsoon was active mainly in the lower latitudes with the northernmost position being at 35°N, 10 degrees south as compared with normal years. The main variation mode was 25 days low frequency oscillation while 30-60 day oscillation was not prominent. After the onset of SCS monsoon, the main moisture transport sources of SCS obviously changed. The high value centers of moisture transportation and convergence stayed in lower latitudes for a long time, which was favorable to the rainbelt maintenance in South China. This situation was closely related to the monsoon wind fields. The anomalous activities of East Asian monsoon play an important role in the anomalous climate of China in the summer of 1997.