Cause and Anomalous Characteristics of the South China Sea Monsoon Trough Producing Heavy Rainfall in South China
摘要: 2007年8月10日第7号台风“帕布”在广东沿海消失后，尾随而上的南海季风槽给华南沿海和台湾岛带来持续多日的暴雨和大暴雨。由于南海季风槽是华南最主要的降水系统，因此研究了8月第3候引发华南大暴雨的南海季风槽的异常特征及其可能的原因。首先分析了季风槽的气候平均时空特征。研究表明低层辐合、高层辐散位于季风槽的南侧，表现了季风槽独立的空间结构特征。南海季风槽强度8月中旬最强。对2007年季风槽的分析表明，该年8月第3候的南海季风槽强度偏强，低层正涡度、辐合以及高层辐散偏强。同时印度季风槽也偏强。南亚高压中心位于青藏高原上空并加强是整个亚洲季风槽增强的主要原因。青藏高原上空增温引起高空东风急流和低空西南季风的加强，增加了华南沿海高空辐散和低空辐合, 对于南海季风槽的加强和维持起着重要的作用。此外，西太平洋副热带高压位于日本上空并且强度偏强，西风带长波槽偏强并向我国西南深入也有利于南海季风槽加强。南海季风槽具有30～60天季节内振荡特征，30～60天大气季节内振荡对南海季风槽向北迁移及加强有重要影响。
Abstract: Atmospheric processes associated with the South China Sea (SCS) monsoon trough which caused the heavy rainfall in pentad 3 of August 2007 in South China are analyzed using the reanalysis data of NCEP and satellite images. The results indicate that the Asian summer monsoon trough has independent space structure, convergence in the low layers and divergence in the high layers are in the south of the Asian summer monsoon trough. The climate analysis shows that both the Indian monsoon trough and the SCS monsoon trough reach their maximum in 〖JP2〗August. The SCS monsoon trough in pentad 3 of August 2007 was located in South China coastal areas and had strong intensity. The convergence in the low layers and divergence in the high layers were also stronger. The Indian monsoon trough was also stronger. The strengthened South Asian high locating over the Tibetan Plateau is the main cause for the strengthening of the Asian monsoon trough. The subtropical high in the western Pacific is located over Japan and is intensified, which is propitous to the northward 〖JP〗movement and the enhancing of the SCS monsoon and monsoon trough. The increased temperature over the Tibetan Plateau induces the stronger easterly in the upper levels, westerly in the low levels,and the enhancing convergence in the low layers and divergence in the high layers of the SCS monsoon trough. The longwave trough in the westerly belt is intensified and extends to Southwest China, which causes the SCS monsoon trough to become stronger. The SCS monsoon trough has an intraseasonal period. The intraseasonal oscillation has an important effect on the northward movement and enhancement of the SCS summer monsoon trough.
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