郑州“7·20”极端暴雨过程中水汽和高低空急流作用机制的数值模拟

Numerical simulation analysis on the influence mechanism of water vapor and upper-low-level jet during“7·20”extreme rainstorm in Zhengzhou

针对郑州“7·20”特大暴雨过程,使用CMA-MESO区域模式对此次极端强降水过程中水汽与高低空急流的影响进行了数值试验分析。结果表明,此次暴雨过程较为成功地被中尺度模式模拟再现;暴雨过程中水汽来源主要为台风“烟花”北侧的东南急流携带的来自西太平洋与印度洋的水汽以及台风“查帕卡”北侧东南气流携带的来自南海的水汽;降水及水汽输送对水汽含量十分敏感,水汽含量微小的变化便会使郑州上空气流辐合区强度减弱,水汽累积减少,降水范围向河南北部缩小,降水强度大幅度减弱;低空急流对应的气流辐合区是郑州上空出现强垂直上升运动中心的主要机制,低空急流减弱后,水汽辐合减弱,降水减少,降水中心位置偏西南,高空急流对降水的影响与低空急流相比较小。

For the heavy rainstorm event in Zhengzhou on 20 July 2021,the influence of water vapor and upper-low-level jet in this extremely heavy precipitation process is analyzed by numerical experiments using the CMA-MESO regional model.The results show that the rainstorm process can be successfully simulated by mesoscale model.The main water vapor sources during the rainstorm are the water vapor from the western Pacific and Indian Ocean carried by the southeast jet on the north side of Typhoon In-fa and the water vapor from the South China Sea carried by the southeast jet on the north side of Typhoon Cempaka.Precipitation and water vapor transport are very sensitive to water vapor content,which shows that the slight change of water vapor content can weaken the intensity of airflow convergence zone over Zhengzhou,reduce the accumulation of water vapor,narrow the precipitation area to the north of Henan,and greatly weaken the precipitation intensity.The airflow convergence zone corresponding to the low-level jet is the main mechanism causing the strong vertical ascending motion center over Zhengzhou.The weakening of the low-level jet makes the convergence of water vapor decrease,which leads to the decrease of precipitation and the location of precipitation center to the southwest.The influence of upper-level jet on precipitation is less than that of low-level jet.