Abstract: Interaction of tropical cyclone and South China Sea (SCS) summer monsoon, especially the mechanism for intensification of low level jet over SCS caused by tropical cyclone landfall, is discussed base on case study and statistical analysis. In case study, different sets of numerical experiments during the landfall of tropical storm BILIS (0604) are carried out using mesoscale model MM5. Result shows that the moist southwestly summer monsoon retarded the decay of tropical cyclone and enhanced the rainfall. On the other hand, the backward reaction from tropical cyclone to low level jet over SCS cannot be ignored. Mesoscale convection systems accompanied with tropical cyclone landfall would enhance the pressure gradient force in low atmosphere over SCS, which would lead to intensification of the low level jet in summer monsoon. Statistical analysis of 30 tropical cyclones with similar track as BILIS dating from 1950 to 2009 also shows that 80% tropical cyclone activities accompany with positive low level wind speed anomaly in SCS.

Key words: tropical cyclone, South China Sea summer monsoon, low level jet, numerical experiment

摘要： 通过个例分析和历史统计, 对热带气旋与夏季南海季风的相互作用进行了研究, 揭示了热带气旋活动导致南海低空急流增强的机制。在个例分析中, 以0604 号热带气旋 “碧利斯”为例, 利用中尺度数值模式 MM5 进行了多组数值模拟实验。结果表明, 强盛的西南季风使热带气旋登陆的维持时间变长, 对热带气旋的降水有显著的增幅作用; 与此同时, 热带气旋对西南季风的作用也不可忽略。在热带气旋登陆过程中引发的一系列中尺度对流系统, 会使得南海上空低层大气的气压梯度力增大, 导致南海季风中低空急流增强。最后, 对 1950?2009 年具有与 “碧利斯”相似路径的30 个热带气旋进行了统计, 发现其中80% 的热带气旋活动伴随着南海区域低空风速的正异常。

关键词: 热带气旋, 南海季风, 低空急流, 数值实验