2018年7月22—23日宁夏暴雨天气过程物理机制诊断分析

Physical Mechanism Analysis of Rainstorm Weather Process in Ningxia from July 22 to 23,2018

利用自动站雨量、MICAPS4调阅的常规资料、NCEP再分析资料以及雷达资料、卫星云图等对宁夏2018年7月22—23日局地暴雨天气中尺度影响系统、物理量场特征、雷达卫星的演变进行分析。结果表明,该次暴雨过程为分股冷空气南下触发的两次暴雨过程。7月22日夜间局地极值暴雨,为暖区降水;23日下午暴雨过程为对流层高层南亚高压东侧北风急流出口区左侧形成强辐散,受低涡影响低层辐合,高低空系统耦合,在台风和副热带高压作用下,造成大气层结不稳定。水汽输送状况及假相当位温、涡度、散度、垂直速度等物理量也充分反映该次降水过程前中低层具有较好的能量储备。22日20:00,700 hPa附近有一正涡度中心,强降水出现在850 hPa上33~35℃K指数高值区内。整层的负速度区和强正涡度区的存在加强了雨强。雷达卫星在两次强降水过程中有较好的指示作用,由雷达回波及卫星云图分析,7月22日夜间强回波在马莲口至岩画长时间的维持(4 h以上),是造成该次局地历史极值暴雨的原因。雷暴单体及超级雷暴单体下击暴流引发阵风锋在短时和临近预报中具有指示性作用。

Using rainfall from automatic station,MICAPS4 data,NCEP reanalysis data and radar data,satellite cloud maps,etc.,we analyzed the local torrential rain characteristics of the mesoscale system,physical field,radar and satellite evolution in Ningxia on July 22 to 23,2018.The results showed that the torrential rain process divided into two process when the cold air invaded:during the night of 22th,the extreme rainstorm was the warm zone precipitation.On the afternoon of 23rd,the rainstorm was caused by strong divergence at the left side of the north wind jet exiting zone on the east side of the South Asia with high pressure in the upper troposphere,the convergence at the lower layer under the influence of low vortices and coupling of the high and low air systems.Under the action of typhoon and subtropical high pressure,the atmospheric junction was unstable.In this process,the conditions of water vapor transportation and physical quantities such as pseudo-equivalent potential temperature,vorticity,divergence and vertical velocity also fully reflected that the middle and low layers had good energy reserves before precipitation.There was a positive vorticity center near 700 hPa,and Ningxia was in the energy zone of 330 to 350 K in 850 hPa,at 20:00 on 22nd.There was a negative velocity zone in the whole layer,and the presence of strong positive vorticity zone strengthened the rain intensity.Radar and satellite had a good indication in the process of two heavy precipitations.The analysis of radar echo and satellite cloud image showed that the strong echo sustained from Maliankou to Rock Paintings for a long time on July 22 was the cause of the local historical extreme rainstorm.The gusty front induced by downburst of single thunderstorm and supercell played an indicative role in short imminent forecast.