由变性台风环流引发的山东特大暴雨天气的位涡场分析

POTENTIAL VORTICITY ANALYSIS OF AN TORRENTIAL RAIN TRIGGRED BY A NEUTERCANE IN SHANDONG PROVINCE

利用PSU/NCAR MM5V3非静力数值模式对1999年8月11～12日由变性台风引发的山东特大暴雨过程进行了较为成功的数值模拟.用模式输出资料,根据位涡理论探讨了这次特大暴雨天气发生、发展的动力学机制.结果表明:西风带弱冷空气侵入台风环流,触发不稳定能量释放是这次特大暴雨形成的重要原因;应用位涡守恒原理能较好地解释特大暴雨和中尺度低涡发生发展的原因,对流层高层位涡扰动是影响中尺度低涡和特大暴雨发生发展的重要因素;345K湿等熵面上风场和气压场的分布揭示了东南暖湿空气沿等熵面爬升与扩散的冷空气相遇,对流强烈发展,产生特大暴雨的物理机制.

By using the numerical model MM5V3,a successful simulation was made for a torrential rain in Shandong province triggered by a neutercane during 11th to 12th in August 1999. Using simulated information and the theory of potential vorticity (PV), the dynamical mechanism by which the torrential rain occurred and developed was analyzed. The results show that weak cold air spreading into the typhoon and tropical convergence stretching northward mainly resulted in the torrential rain. The conservation theory of PV can well explain why the torrential rain and mesoscale vortex occurred and developed. The PV disturbance of the upper troposphere is an important factor for the mesoscale vortex and torrential rain to occur and develop. The wind and pressure on the 345K isentropic surface revealed physical mechanisms that see southeastward warm-moist flow uplifting along the isentropic surface and meeting with descending cold air, which resulted in convection and the torrential rain.