近海台风对“21·7”河南极端暴雨过程水汽通量和动、热力条件影响的模拟

A Numerical Simulation on the Impacts of the Offshore Typhoons on Water Vapor Flux,Dynamic and Thermal Conditions of the Extreme Rainstorm Event in Henan Province in July 2021

本文利用WRF模式对近海台风“烟花”及“查帕卡”影响2021年7月19日至21日河南极端暴雨的过程进行数值模拟。控制试验(CTL)对台风路径、强度、大尺度环流形势,以及河南暴雨的强度和空间分布型等均给出合理的模拟,基本再现了本次河南极端暴雨的发展过程。敏感性试验表明,在移除台风“烟花”后,副热带高压系统显著南压并在南侧形成东南风急流,河南地区的南风分量减弱、东风增强,东西方向的水汽输送占主导,有利于降水分布型由CTL试验的南—北向转变为东—西向;另一方面,由于低层东南风急流相较于移除“烟花”前的东风急流偏弱,河南降雨区的局地辐合减弱,水汽通量净流入值较CTL试验降低5.81%,且中纬度冷气团西移减慢,引起局地相当位温梯度减弱,最终导致移除台风“烟花”试验的降雨强度偏弱。移除台风“查帕卡”后,大尺度环流形势几乎未受影响,河南南侧的水汽输送略有减弱,因此强降水分布基本与CTL试验类似,降雨强度略有减小。与台风“烟花”相比,“查帕卡”对河南暴雨的影响较弱。

This study uses the WRF model to numerically simulate the influence of offshore typhoon In-Fa and typhoon Cempaka on the extreme rainstorm process in Henan on 19–21 July 2021.The control(CTL)experiment reasonably captures the tracks and intensities of the two typhoons,the large-scale circulation pattern,the intensity,and spatial distribution pattern of the rainstorm event in Henan,basically reproducing the extreme rainstorm process in Henan.In addition,the sensitivity experiments indicate that after the removal of typhoon In-Fa,the subtropical high extends southward and forms the southeast wind jet in the south,causing the south(east)wind component to obtain weakened(strengthened)around Henan.The water vapor transport in the zonal direction becomes dominant,which is conducive to the transition of the rainfall distribution from the south–north orientation in CTL to the east–west orientation.On the other hand,given that the southeast wind at the low level is weaker than the easterly jet before the removal of typhoon In-Fa,the local convergence at the Henan rainfall area is weakened,and the net water vapor flux is reduced by 5.81%compared with that in CTL experiment.The slowdown in the westward movement of the mid-latitude cold air causes the reduction of the local equivalent potential temperature gradient.Therefore,the rainfall intensity in the removal of typhoon In-Fa experiment is relatively weaker than that in CTL.After the removal of typhoon Cempaka,the large-scale circulation characteristics are almost unaffected,and the water vapor transport on the south side of Henan is slightly weakened.Therefore,the distribution of heavy rainfall is similar to that in CTL,with a slight decrease in rainfall peak.Compared with typhoon In-Fa,typhoon Cempaka has less effect on the rainstorm event in Henan.