1999年夏季长江及以南地区洪涝的大尺度环流成因初探

通过对比分析，探讨了1999年夏季长江及以南地区洪涝灾害的环流成因，指出1999年处在La Nina年，西太平洋副热带高压偏弱，偏北且异常偏东；南海夏季风前期偏强，后期偏弱；带对流层上部南亚高压脊和洋中槽位置偏南；对流层下部长江下游至江南受气旋性异常环流影响，形成异常加强的水输送圈；夏季亚洲中纬度大陆高压维持，中低纬度环流系统的共同作用造成长江中下游及以南地区的洪涝灾害。

Preliminary Study on Circulation Cause of Abnormal Rich Precipitation in and to the South of Yangtze River in Summer of 1999

Circulation characteristics associated with abnormal rich precipitation in and to the south of Yangtze River basin in summer of 1999 were discussed. The following circulation characteristicswere noticed: During the sustained stage of La Nia period, the intensity of WestPacific subtropical high (WPSH) was belownormal with its position more moving northward and eastward. The tropical monsoon over South China Sea was stronger in earliersummer, butweaker later. In upper troposphere, South Asia anticyclone ridge and TUTT located something south. Meanwhile, in lower troposphere,the enhanced transportation of water vapor was formed by the cyclonic abnormal circulation over mid to low reach of Yangtze River and to the south of Yangtze river valley. In the summer, the continental high persisted in the mid latitude region of Asia. Mid and low latitude circulation anomalies syntheticallycause the flooding around and to the south of Yangtze river basin.