两次西行热带气旋影响云南降水对比分析

利用常规观测资料、中国气象局上海台风研究所(CMA-STI)热带气旋最佳路径数据和FY-2C卫星云图观测资料,以0608台风派比安和0809强热带风暴北冕两个西行热带气旋影响云南降水为例,通过其路径、降水量、移动速度、环境场和物理量场的对比分析,结果表明:两次台风源地、移动路径及登陆地点、影响时段、最大降水落区相同,但影响时间长度、影响范围和造成的灾害程度后者强于前者;西南季风与热带辐合带(ITCZ)较活跃,副热带高压西伸增强,并有低空急流、辐合区配合台风低压环流共同作用是热带气旋导致云南强降水的重要天气背景;云图中尺度分析发现,多种系统的共同作用,导致台风环流持久不消,进而易激发多个α-中尺度对流系统(MαCS)和β-中尺度对流系统(MβCS)云团生成并持久维持,是台风低压强降水发生的直接原因;物理量场的诊断分析表明,活跃的季风系统,使孟加拉湾和南海构成强大的水汽通道,伴随低空急流的建立和增强,致使大量不稳定能量和水汽向云南输送,在云南形成条件性对称不稳定(CSI)和深厚斜压性的正反馈机制,是导致云南强降水的重要物理机制。

Comparative Analysis of the Precipitation Caused by Two Landing Tropical Cyclones in Yunnan

Yunnan is a typical monsoon climate area located in the low latitude highland in China, affected by South Asia monsoon and East Asia monsoon at the same time. The heavy rainfall in Yunnan has peculiar area characteristic because of special geographic location and landform. In summer, the landing westbound TC from the South China Sea is one of the most important weather systems causing heavy rainfall in Yunnan. Statistics indicate the extreme heavy rainstorm in Yunnan is mostly caused by weaken landing TC, so its important to research mechanisms of landing TC heavy rainfall on the plateau. In 2006, the typhoon class TC Prapiroon, lands westbound and weakens into tropical depression in Yunnan without causing heavy precipitation. But in 2008, another TC Kammuri of the same strength causes eight days continuous precipitation, and a two day course of large-scale heavy precipitation in Yunnan Province. With the conventional observation data, best track data of CMA-STI and FY-2C satellite images and TBB, the precipitation caused by Prapiroon (0608) and Kammuri (0809) are compared on track, rainfall, speed, the circulation and hydrodynamic field. The result shows that they have similar birthplace, track, landing place, affecting time and central precipitation falling area, but Kammuri has much greater impacts on the length of time, the scope and impact of disasters. Active southwest monsoon and ITCZ, southerly low level jet, westward moving subtropical high and convergence ascending region, contribute to the major weather background of tropical cyclone precipitation in Yunnan. Effected by a variety of systems together, the typhoon circulation is very durable, resulting in the formation and maintenance of MαCS and MβCS clouds, leading to the occurrence of precipitation. Diagnosis on these physical fields shows that as a result of the active monsoon system, the Bay of Bengal and the South China Sea constitute a powerful water channel, through which instability energy and water vapor are transported to Yunnan accompanied by the establishment and enhancement of low-level jet. CSI and deep convection of positive feedback mechanisms lead to heavy precipitation in Yunnan.