台风榴莲（2001）生成初期中尺度涡旋合并过程研究

由于热带海洋上观测资料的稀缺和热带气旋系统本身发生、发展的复杂性,热带气旋生成机制研究领域至今仍然存在很多未解之谜。已有的观测和模拟研究证明,中尺度涡旋合并过程对于热带气旋的生成可能有触发作用,但尚未见到南海季风槽内热带气旋生成过程中中尺度涡旋合并现象的实例模拟研究。利用新一代中尺度天气研究与预报模式WRF对南海热带气旋榴莲(2001)生成过程中的中尺度涡旋合并过程进行了高分辨率(4 km)数值模拟,并与观测资料进行对比,利用模式输出结果重点分析两个中尺度涡旋合并过程中的主要动力学和热力学特征,并在此基础上进一步分析了合并过程中系统中心附近涡度方程中各项涡度收支的演变情况,最后通过两个敏感性试验与控制试验结果的对比,初步探讨中尺度涡旋合并过程对于热带气旋榴莲生成的作用。结果表明,南海季风槽中的新生中层中尺度涡旋V2,是榴莲生成过程中的主导涡旋,预先存在的东部低层的中尺度涡旋V1对于台风榴莲的生成则起到了辅助作用,两个不同高度的涡旋合并叠加促使涡度的辐合、辐散项率先在低层引起涡度的快速增长,随后垂直输送项在对流层中层对涡度的增长起主要作用。两个涡旋的最终合并,使热带气旋系统正绝对涡度在垂直方向上从低层到中层得以贯通,进而触发榴莲的生成。

A study of the role of mesoscale vortex merging in the genesis of Typhoon Durian (2001)

The tropical cyclone is one of the most destructive natural phenomena on the Earth.The mechanisms for the tropical cyclone genesis remain enigmatic and controversial,because of the lack of observations over the tropical oceans and the complexities of tropical cyclone lifecycle.Some observations and numerical studies indicate that the mesoscale vortex merger is a possible triggering mechanism for the tropical cyclone genesis.So far,however,there has been no real-case numerical simulating study on the vortex merger in the monsoon trough over the South China Sea.In this study,a high resolution simulation(4 km) is conducted to investigate the vortex merger process during the formation of the tropical cyclone Durian(2001) over the South China Sea by using the Weather Research and Forecasting(WRF) Model.The model verification shows that the formation and the development of Durian were reasonably reproduced.Consequently,the characteristic of the vortex merger was analyzed.Then the time series of vorticity budget were investigated.Moreover,two sensitivity simulations were performed to examine what role the merger process played in Durian’s formation.The results reveal that the mid-level vortex V2 which formed after 30 h integral is the main vortex for Durian’s genesis and that the low-level vortex V1 which preexisted at Philippines makes just an assistant contribution to its genesis.During their merger,the vorticity divergence first intensified at low level,and then the vertical advection transported positive vorticity to the mid-level.Their final merger accelerates vertically the establishment of positive vorticity,leading to Typhoon Durian’s formation.