山西晋城一次暖区大暴雨成因分析

Cause Analysis of a Warm-Sector Extreme Heavy Rainfall Event in Jincheng, Shanxi Province

摘要: 北方暖区暴雨预报是天气预报的一个难点。2012年7月30日夜间，山西晋城出现一次突破历史极值的暖区极端强降水，导致严重涝灾。利用常规和非常规探测资料，对此次极端强降水成因进行了综合分析，结果表明：此次大暴雨过程发生在东高西低的环流形势下，是高空急流、西风槽、日本海高压、低层“人”字形切变线、远距离台风等系统共同作用的结果，大暴雨发生在高空分流场伴随的强辐散气流之下、低层切变线附近。晋城周边环境条件有利于深厚湿对流的产生和发展，极端降水区周边具有深厚湿对流潜势。造成晋城城区的强降水云团是一个稳定少动的β中尺度对流系统，强降水出现在TBB等值线长轴两侧、接近TBB等值线低值中心的区域；在晋城强降水时段，中尺度辐合线在晋城附近稳定少动，不断触发对流；对流回波长轴方向与回波移动方向接近平行，列车效应显著；对流回波具有明显的后向传播特征和低质心的热带降水回波特点。山西南部风场自身的气旋式辐合、太行山地形的动力抬升及辐合作用为强降水的发生提供了有利的动力条件。基于雷达观测的短临预报可以弥补数值预报对中小尺度系统预报能力的不足，提高暖区暴雨的预报准确率。

Abstract: The forecasting of warm sector heavy rainfall in northern China is a difficult problem. On the night of July 30, 2012, a warm-sector extreme heavy rainfall occurred in Jincheng, Shanxi province, which broke the historical extreme value and caused severe flooding. In this paper, the extreme strong precipitation process causes were analyzed by using conventional and unconventional observation data. The results showed that the torrential rainfall was the result of the combined action of the upper jet, west wind trough, Japan Sea high pressure, low-level cold shear line and warm shear lines, long-distance typhoon. The torrential rain occurred under high-level distribution field with strong divergence airflow, near low-level shear line. The surrounding environment conditions of Jincheng were favorable for the generation and development of deep wet convection, and the surrounding area of extreme precipitation area had deep wet convection potential. In the period of heavy rainfall in Jincheng, the mesoscale convergence line was stable and less moving around Jincheng, and the convection was continuously triggered. Since the directions of the echo long axis and echo movement were parallel, train effect was obviously seen during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which were similar to tropical heavy rainfalls. The cyclonic convergence of the wind field in southern Shanxi and the dynamic uplift and convergence of the Taihang mountain topography provided favorable dynamic conditions for the occurrence of heavy precipitation. The short-time forecast and nowcasting based on radar observation could effectively compensate the lack of ability in finding mesoscale and small-scale systems by NWP models, which may improve the accuracy of forecasting warm sector rainfalls.