一次鄂豫川陕交界处短时暴雨诊断分析

Diagnostic Analysis of a Short-time Rainstorm at the Junction of Four Provinces

应用常规高空和地面观测资料、FNL(1o×1o)逐6 h再分析资料,对2016年6月23日发生在副热带高压外围由冷锋触发的一次暴雨机制进行综合诊断分析。结果表明:本次暴雨降水时段集中,主要是发生在午后到傍晚,且小时雨强大,具有明显的突发性特征。通过对湿位涡的时间演变和空间分布分析发现,强降水开始于对流层中低层MPV1由负值向正值逐渐转换时期,以及MPV2由正值向负值开始转变的过渡时期;强降水区主要位于MPV1 <0与MPV2> 0的重叠的区域,同时正、负值过渡区域等值线最密集处也与本次过程中两个暴雨中心落区有较好的相对关系。本次降水过程中锋生函数的各项在中低层共同作用于锋生,倾斜项的贡献要大于水平散度项和水平变形项,同时在短时暴雨开始发生时总锋生函数在暴雨区明显增大。降水过程中,锋面触发暖湿气流爬升,与高低空急流耦合构成的次级环流的上升支位置重合,进而在地面锋前形成深厚而宽广的上升运动,这为本次短时暴雨的产生提供了有利的动力条件。

Using conventional upper air and ground observation data, FNL reanalysis data(1 °×1 °), the mechanism of a heavy rain triggered by cold front in the periphery of the WPSH on June 23, 2016 was diagnosed and analyzed. The result showed that:This rainstorm mainly occurred in the afternoon to evening, and the hourly rain was strong, with obvious sudden characteristics. By analyzing the temporal evolution and spatial distribution of moist potential vortices, it is found that the heavy precipitation begins in the transition period from negative value to positive value of MPV1 in the middle and lower troposphere, and the transition period from positive value to negative value of MPV2. The area where the boundary of the positive and negative with most density contour was related to two rainfall centers in rainstorm. In this process, the various frontogenesis functions acted on frontogenesis together in the middle and lower layers, and the contribution of the tilt term was greater than that of the horizontal divergence term and the horizontal deformation term. At the same time, the total frontogenesis function increased significantly in the rainstorm area when the short-time rainstorm began to occur. The front surface triggered the warm and humid air current to climb, which coincides with the ascending branch of the secondary circulation formed by the high-low-altitude jet stream. And then formed a deep and broad ascending motion in front of the ground front, which provides a favorable impetus for the generation of this short-term rainstorm condition.