摘要:利用MICAPS观测降水数据、欧洲气象中心ERA5再分析资料和FY-4A卫星云顶亮温数据，对2021年7月20日河南极端暴雨进行综合分析。结果表明，此次暴雨受200 hPa两槽一脊、大陆高压、副热带高压（副高）西伸北抬和台风“烟花”西移、“查帕卡”台风倒槽等多尺度天气系统共同影响，黄淮气旋的西南气流与副高和“烟花”之间的东南气流稳定控制河南地区，边界层急流供应充沛水汽，在太行山和嵩山迎风坡辐合抬升，致使河南暴雨长时间维持，产生极端降水量。西南气流穿过从广东和广西延伸到河南的高湿带，副高和“烟花”引导东南气流经过从东海洋面延伸到河南的相对较弱湿区，这两条水汽输送带在太行山和嵩山地形阻挡下汇合在河南北部，为暴雨供应水汽。丰富的可降水量、水汽过饱和、深厚暖云层以及降水系统较强的水汽消耗率为郑州高降水效率提供有利条件。郑州低层大气经历多次从强层结不稳定到弱层结不稳定的转化，边界层急流引起的垂直风切变和气流辐合对层结稳定度变化有重要影响。黄淮气旋内部中尺度涡旋对河南暴雨发生发展至关重要，不但提供西南气流，还产生较强的位势高度纬向平流，增强边界层急流。嵩山与太行山余脉构成喇叭口地形，边界层急流在嵩山北侧和东侧爬坡，促使山前水汽堆积，激发和加强暴雨。中尺度云团合并小尺度云团，发展成结构密实的孤立云团，稳定少动，对暴雨有重要影响。降水区上空广义湿位涡异常，由于广义湿位涡能够刻画中尺度系统的垂直风切变、涡度以及大气湿斜压性和层结不稳定等动力和热力因素垂直结构特点，所以对中尺度系统和降水落区有一定指示意义。
关键词:极端暴雨/
中尺度涡旋/
边界层急流/
广义湿位涡
Abstract:We conducted a comprehensive analysis of the extreme rainstorm that occurred in Henan Province on July 20, 2021, using MICAPS observation precipitation data, European Meteorological Center ERA5 reanalysis data, and cloud-top brightness temperature from Satellite FY-4A. The results showed that the extreme rainstorm was affected by multi-scale weather systems, as follows: two troughs and one ridge at 200 hPa, a continental high, the western extension and northern lifting of subtropical highs, the westward movement of Typhoon In-Fa, and the inverted trough of Typhoon Cempaka. The southwesterly airflow of the Huanghuai Cyclone and the southeasterly airflow between the subtropical highs and Typhoon In-Fa had firm control over the Henan region. The boundary layer jets supplied abundant water vapor, which converged and uplifted on the windward slopes of the Taihang and Song Mountains and resulted in extreme precipitation falling over a long duration. The southwesterly airflow passed through a high humidity zone extending from Guangdong and Guangxi to Henan. In addition, the subtropical highs and Typhoon In-Fa guided the southeasterly airflow through a relatively weak moist area extending from the Eastern Ocean to Henan. Blocked by the terrain of Taihang and Song Mountains, the two water vapor conveyor belts converged in northern Henan, which supplied the water vapor for the heavy rain. Abundant precipitable water, supersaturated water vapor, deep and warm clouds, and a high rate of water vapor consumption in precipitation system provided favorable conditions for the high precipitation in Zhengzhou. The lower atmosphere over Zhengzhou was repeatedly transformed from strong to weak due to the unstable atmospheric stratification, and the vertical wind shear and convergence associated with the boundary layer jet critically influenced the atmospheric stratification stability and changes. The mesoscale vortex within the Huanghuai Cyclone was vital to the initiation and development of the torrential rainfall in Henan, and it not only provided the southwesterly airflow but also generated the strong zonal advection of the geopotential height, which enhanced the boundary layer jet. Furthermore, the trumpet-shaped topography of Song Mountain and the offshoot of Taihang Mountain caused the boundary layer jets to ascend the northern and eastern sides of Song Mountain, which promoted the accumulation of water vapor at the front of the mountain, and this, in turn, initiated and strengthened the rainstorm. Mesoscale cloud clusters merged with small-scale cloud clusters and developed into densely structured and isolated cloud clusters; these were stable, their movements were relatively slow, and they had a critical impact on the torrential rainfall. The generalized moist potential vorticity (GMPV) over the precipitation area was anomalous. The GMPV describes the vertical structure characteristics of vertical wind shear, vorticity, and dynamic and thermal factors (such as atmospheric moist baroclinicity and stratification instability of the mesoscale system), and it is thus of great significance for identifying the mesoscale system and precipitation within the region.
Key words:Extreme Rainstorm/
Mesoscale vortex/
Boundary layer jet/
Generalized moist potential vorticity
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