AN ANALYSIS OF THE 500 HPA SIGNAL FIELD FOR HEAVY RAINFALL EVENTS OVER THE MIDDLE REACHES OF THE YANGTZE RIVER IN CHINA

The signal field of 500 hPa anomalies for the heavy rainfall events was analysed over the Middle Reaches of Yangtze River, China. At test for the composit e signal field has been developed. The analysis of the 1977-1999 observational data implies that the appearance and distribution of anomaly in the 500 hPa signal field is an important precursory signal of heavy rainfall. The analysis of the composite signal field of 14 heavy rainfall cases indicates that on the first d ay of a heavy rainfall event, a positive anomaly occurred over the northwest of China (40°-50°N, 80°-100°E), and another over the south of China (20°-25°N , 100°-130°E), while a negative anomaly occurred over the area northern of the Middle Reaches of Yangtze, i.e., (30°-50°N, 100-150°E). Thus, a wave patter n +-+has been identified from the northwest to the southeast in China.