2005年6月湖南大暴雨过程的天气动力学诊断分析

利用NCEP分析资料和实测资料，对2005年6月初湖南大暴雨过程进行了天气动力学诊断分析。结果表明：暴雨区中上升运动和水汽辐合均大于周围区域，中低层为对流不稳定层结。暴雨区位于非地转湿Q矢量辐合强迫的次级环流上升支中，其南北两侧为非地转下沉气流，下沉气流的补偿有利于暴雨系统的维持。非地转湿Q矢量辐合区对6小时暴雨落区预报有指示意义。暴雨区位于700hPa湿位涡和850hPa湿相对位涡负值中心附近偏暖湿气流一侧。低层暖湿平流和强上升运动致使低层湿空气辐合补偿、热量上传，利于高层辐散增强，抽吸作用加强低空辐合，促使暴雨发展。

Diagnostic Analysis of Heavy Rainfall in Hunan Province in June 2005

A heavy rainfall in Hunan Province in June 2005 is diagnosed based on NCEP/NCAR reanalysis data and observational data. The results show that the most intensive moisture convergence, the strongest ascending movement and the most instable convection stratification all occur in the rainfall center. The heavy rain region locates at the rising branch of a secondary circulation forced by the convergence of the ageostrophic wet Q-vector. Descending flows prevail at the south and north sides of this convergence center and produce a compensation effect, which is favorable for maintaining the heavy rainfall. Convergence of the ageostrophic wet Q-vector has a forecast significance for the coming 6h rainfall area through producing a secondary circulation and reinforcing the storm. The rainfall occurrs at the warm and wet side of the negative value center of the moist potential vorticity (MPV) at 700 hPa and relative MPV at 850hPa. The warm and wet advection and the strong ascending movement at lower level lead to the compensation of the moist air and the upward transport heat, and strengthen the high-level divergence and low-level convergence, which ultimately reinforce the storm.