Role of Summer Monsoon in Anomalous Precipitation Patterns During 1997 Flooding Season

By means of daily precipitation data and T63 reanalyzed 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.