陕西榆林一次大暴雨成因分析

Analysis on the Cause of a Rainstorm in the North of Shaanxi Province

利用常规气象观测资料、陕西区域自动站观测资料、NCEP 1°×1°再分析资料和卫星雷达探测资料,对2017年7月25—26日陕北榆林一次大暴雨进行了诊断分析,结果表明:本次过程以对流性强降水为主,在副热带高压控制下,300 hPa高空急流增强南压、河套地区弱的高空短波槽东移配合低层偏南风增大为本次大暴雨产生提供了有利的背景场。远距离台风外围偏南气流为强降水提供了充沛的水汽和能量,东路水汽输送进一步增强了大气整层可降水量。高层有值为0.2 PVU正值位涡扰动沿假相当位温密集区下滑,与低层东路冷空气共同加剧了大气的对流不稳定性,导致若干个中小尺度对流系统合并发展成一椭圆形MCS,MCS最强时段TBB≤52℃冷云罩面积达1.6×105 km^2,强降水区位于MCS合并处及中心附近。对流单体造成榆林市子洲县第一阶段强降水",列车效应"是造成子洲第二阶段强降水主要原因。

In this study, we analyzed a regional rainstorm of Yulin City, Shaanxi during 25th-26th July 2017 with the conventional data, regional automatic station data, NCEP 1°×1°reanalysis data and the observations of satellite and radar, the results show that: this weather process was dominated by convective heavy precipitation. Under the control of subtropical high, the 300 hPa jet stream was strengthened and moving southward. Meanwhile, the southerly airflow around the long-distance typhoon provides abundant water vapor and energy for heavy precipitation, and the water vapor transport along the east road further enhances the atmospheric precipitable water. The convective instability was enhanced by the decline of upper-level positive potential vorticity was about 0.2 PVU disturbance along the intensive areas of the potential pseudo-equivalent temperature and the low-level cold air from the east, which resulted in the merging of small mesoscale systems, and developed into the mesoscale system. In the mature stage, the area of cold cloud cover the area 6×105 km^2, and the TBB was less than -52 °C. The heavy rainfall was located at the merging area and the center of mesoscale system. The first stage of the precipitation process in Zizhou County of Yulin was caused by convective monomer, furthermore, the second stage is caused by “Train Effect”.