中国东南部5—8月持续性强降水和环流异常的准双周振荡

The quasi-biweekly oscillation characteristics of persistent severe rain and its general circulation anomaly over southeast China from May to August.

中文关键词:  中国东南部，持续性强降水，低频降水，低频大气环流

英文关键词:Southeast China, Persistent severe rain, Low frequency rainfall, Low frequency circulation

中文摘要:

      利用1979—2009年夏季（5—8月）中国站点逐日降水资料、NCEP/NCAR大气再分析资料以及向外长波辐射（OLR）资料，分析了中国东南部夏季持续性强降水的低频特征及其伴随的低频大气环流形势，利用超前滞后合成的方法对该低频信号的来源和传播特征进行了研究。结果表明：中国东南部夏季降水存在明显的准双周低频振荡，低频降水事件（持续性强降水）在6月10日前后和7月1日前后发生的次数较多，持续5 d的低频降水事件降水量占总低频降水事件的比例最大。在低频降水事件发生时期，中国东南部在低层是很强的低频气旋式环流，而在中国南海至西太平洋一带则是强大的低频反气旋，同时低频的水汽从孟加拉湾北部以及中国南海、菲律宾海一带输送到长江以南地区强烈辐合上升；此时在高层一个低频反气旋控制中国东北部地区，该低频反气旋与其西侧的低频反气旋以及位于中国东南沿海的低频气旋相互配合，使得长江以南地区高层强烈地辐散，加强了低层的上升运动。在超前低频降水7 d左右时，大气低层在150°E洋面附近开始出现低频反气旋，逐渐加强并向西移动到达中国东南沿海，而在中国南海一带的低频气旋则向西北移动到长江以南地区，与此同时，副热带高压有一个明显的西伸过程，高低层相互配合最终导致低频降水的发生。

英文摘要:

      The low frequency characteristics of persistent severe rain from May to August over southeast China (SC) and its associated low frequency general circulation are studied using the daily rainfall station data in China, the OLR data and the NCEP/NCAR reanalysis data. The source and propagation of the low frequency signal are also investigated by the composite analysis. The results show that the summer rainfall over SC has the characteristics of quasi-biweekly oscillation. The number of persistent severe rain events gets its peak around June 10 and July 1. The precipitation of five-day low frequency rain events takes up the largest ratio of all low frequency events. In the lower atmosphere a strong low frequency cyclonic circulation is located over SC, while a strong low frequency anticyclone is over the South China Sea (SCS) to the western North Pacific region. The persistent low frequency water vapor is supplied from the Bay of Bengal, SCS and the Philippine Sea, and converges to the south of the Yangtze River. At the same time, a low frequency anticyclone controls northeast China in the upper troposphere. This circulation coordinating with a low frequency anticyclone west of it and a low frequency cyclone located around the coastal waters, is favorable to a divergence environment over SC. Thus, the upward motion is enhanced. About 7 days before the low frequency rainfall, there was a low frequency anticyclone over about 150°E in the lower levels and it strengthened and propagated to the coastal waters of southeast China, while the low frequency cyclone over the SCS propagated northwestward to SC. At the same time, the western Pacific subtropical high had an apparently westward extension.The lower and upper circulations coordinating with each other resulted in the low frequency rainfall over SC.