对华北一次特大台风暴雨过程的位涡诊断分析

THE DIAGNOSIS ANALYSIS OF POTENTIAL VORTICITY FOR A SEVERE TYPHOON RAINSTORM IN NORTH CHINA

通过对 960 8号台风低压及其外围暴雨位涡和等熵面上物理量场的分析 ,揭示了台风低压北上诱发暴雨过程的位涡场的结构及冷空气对暴雨增幅的作用 ,给出此次暴雨增幅过程的图像。分析表明 :对流层低层中高纬度冷空气 (高位涡 )扩散南下在台风低压环流区附近的“侵入”作用是此次特大暴雨过程的最重要的原因之一 ;等熵面位涡的分析进一步说明了中高纬地区冷空气的活动状况 ;对流层高层或平流层低层高位涡的下传有利于位势不稳定能量的释放 ,使得暴雨增幅。分析也发现 :特大暴雨落区位于低层等熵面位涡高值区的东北侧 ,与中低层位涡斜压部分最大负值区相对应 ,并且随着位涡斜压部分负值中心强度的增强而增幅 ,这为暴雨强度和落区的预报提供了一定的参考。

Based on the analysis of potential vorticity ( PV ) and elements on isentropic surface about the typhoon 9608 and its heavy rain outside, the study is to show the PV structure and the interaction with midlatitude weather systems. It shows the feature of severe rainstorm dynamic and thermodynamic process. A picture about the process of heavy rain amplification is given. It is also shown that one of the most important reasons of the heavy rain amplification is the cold air (high PV region) which spreads to south from midlatitude in the lower troposphere and transports into the typhoon low pressure. The study of PV on isentropic surface shows the active state of the midlatitude cold air. The tropopause folding, which means that high PV spreads downward from the upper troposphere or stratosphere, helps the releasing of potential instability energy and the development of rainstorm. It also indicated that the rainstorm region lies in the northeast part of high PV center on the lower isentropic surface, corresponding to the maximum negative region of the PV baroclinic part, and supplies an important reference for forecasting the intensity and the region of the typhoon heavy rain.