2021年8月17—18日玉树东部地区中到大雨天气过程的成因分析

Cause Analysis of Moderate to Heavy Rain Weather Process in Eastern Yushu during August 17-18, 2021

基于高空、地面和雷达等资料,对2021年8月17—18日发生在玉树东部地区的一次中到大雨天气过程进行了分析,结果表明:(1)此次过程是2021年入汛以来范围最广的一次强降水天气过程,强降水站点较为分散;夜雨、降水时间相对集中,具有一定的对流性质。(2)这是一次副高、南亚高压、切变线和冷空气共同影响下的天气过程。系统维持时间较长,高能高湿,地面辐合线和冷空气触发强降水。积云层状云混合降水回波,最强反射率因子53.5 dBz。反射率因子梯度大值区降水明显;低层存在速度辐合,有利于回波加强。(3)探空图呈现“瘦高型”,CAPE值大,湿层深厚;玉树处于冷暖平流交汇区;水汽辐合明显,东南部的比湿大于西北部;降水区地面至200 hPa上升气流强且深厚。(4)降水云系呈顺时针移动发展,垂直风切变弱,持续时间较长;强降水位于温度梯度大值区。

Based on the data of high altitude, ground and radar, a moderate to heavy rain weather process occurred in eastern Yushu from August 17 to 18, 2021was analyzed. The results showed that:(1) This process was a heavy precipitation weather process with the widest range since the flood onset of 2021, and the heavy precipitation stations were scattered;Night rain, precipitation time was relatively concentrated, had a certain convective nature.(2) This was a weather process under the joint influence of subtropical high, South Asian high, shear line and cold air. The system maintains for a long time, high energy and high humidity, ground convergence line and cold air trigger heavy precipitation.Accretionary cloud mixed precipitation echo,the strongest reflectance factor 53.5 dBz.Precipitation was obvious in the large value area of reflectance factor gradient. There was velocity convergence in the low layer, which was conducive to echo strengthening.(3) The radiosonde shows “lean and tall type”, with large CAPE value and deep wet layer;Yushu was located in the intersection of warm and cold advection;The moisture convergence was obvious, and the specific moisture in the southeast was greater than that in the northwest. The updraft from the ground to 200hPa in the precipitation area was strong and deep.(4) The precipitation cloud system moved clockwise, and the vertical wind shear was weak and lasted for a long time. Heavy precipitation was located in the large value region of temperature gradient.