四川2020年8月16日暴雨天气过程动力诊断

Diagnostic Analysis of Rainstorm in Sichuan Province on August 16, 2020

利用气象站常规观测资料、欧洲气象中心(ECMWF)第五代大气再分析数据资料(ERA5),基于天气学诊断分析方法,选取垂直螺旋度、湿位涡和准地转Q矢量及其散度对发生在2020年8月16日四川地区的一次特大暴雨天气过程进行分析,结果如下:1) 垂直螺旋度分析表明:高层为垂直螺旋度负大值区,中低层为正大值区,使高低层“抽吸作用”得以加强。2) 对流层低层湿正压项(MPV1)负值区与湿斜压项(MPV2)正值区相对应,反映出大气层结的斜压不稳定性,在剖面图上能够体现出和负大值区暴雨落区的经向分布,且湿斜压项的正值区也反映出低层有暖湿气流的活动。3) 准地转Q矢量及其散度的辐合区和负大值区表示具有强烈的上升运动,且上升运动从低层延伸至150 hPa高度以上,强度大且厚度深,有利于低层水汽的垂直向上输送。

Utilizing conventional observation data from weather stations, the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation atmospheric reanalysis (ERA5), based on synoptic diagnostic analysis methods, selecting vertical helicity, moist potential vortex, quasi-geostrophic Q vector and its divergence were analyzed for a heavy rainstorm that occurred in Sichuan on August 16, 2020. The results showed that: 1) The vertical helicity analysis shows the high-level negative large areas, middle and low level positive large areas of vertical helicity, so that “effect of pumping” is strengthened. 2) The negative value area of MPV1 in the low troposphere corresponds to the positive value area of the MPV2, reflecting the baroclinic instability of atmospheric stratification. The profile can reflect the meridional distribution of the rainstorm area, and the positive value area of MPV2 at the low-level also reflects the activity of warm and humid airflow in the low-level. 3) The quasi-geostrophic Q vector and its divergence shows that the convergence zones of the quasi-geostrophic Q vector and the negative large areas of quasigeostrophic Q vector divergence indicate the strong ascending motion, and the upward motion extends from the low-level to the height of 150 hPa higher. The intensity of the upward motion is high, and the thickness is deep, which is conducive to the vertical upward transportation of moisture in the low-level.