南海夏季风对强热带风暴Bilis(0604)引发暴雨的影响

Bilis(0604)是一个登陆后长久维持并造成了特大暴雨的强热带风暴.通过对常规观测资料、雷达资料和红外卫星云图的分析,发现暴雨过程中不断有中尺度对流系统(MCSs)产生和发展,这些MCSs是造成强暴雨的主要中尺度系统.在此基础上用中尺度模式MM5对Bilis登陆后66 h的过程进行了数值模拟,模拟的雨带和雨量与实况较符合.利用模拟结果,对MCSs的发展过程和特征作了分析,发现Bilis的低压环流和南海夏季风在华南一带交汇,使得华南一带多中尺度涡旋、辐合中心和中尺度辐合线发展,这些系统为中尺度对流系统的生成和维持提供了有利的环境.敏感性试验表明,南海夏季风输送暖湿气流为暴雨区补充不稳定能量和水汽,对暴雨的产生具有十分重要的作用.     

THE INFLUENCE OF SOUTH CHINA SEA SUMMER MONSOON ON THE RAINSTORM ASSOCIATED WITH THE LANDFALLING STRONG TROPICAL STORM BILIS (0604)

Bilis （0604） is a strong tropical storm that sustained over land for a long time, bringing torrential rain. With conventional observation data, radar data and infrared satellite imagery, Mesoscale Convective Systems （MCSs） are found to form and develop successively, which cause torrential rain. Then numerical simulation is conducted using MM5 to simulate a 66-h post-landfall process. The simulated distribution and intensity of precipitation match the observation well. With the simulated result, the characteristics and process of MCS development are analyzed with the finding that the convergence of the tropical depression and South China Sea （SCS） summer monsoon over The south of China causes the formation of a mesoscale vortex, mesoscale convergence center and mesoscale convergence line, which are favorable to the development and sustaining of the MCSs. A sensitivity experiment indicates that the SCS summer monsoon transports unstable energy and water vapor continuously, which is of vital importance to rainstorms.