高空急流与副急流演变及其与河南2021年“21·7”特大暴雨的关系

Evolution of the Upper-Level Jet and Sub-jet and Their Relationships to the"21·7"Henan Rainstorm in

利用中国气象局所提供的逐小时的站点降水资料与欧洲中期天气预报中心所提供的逐小时、0.25°(纬度)×0.25°(经度)的ERA5再分析数据,重点研究了产生郑州极端小时降水的关键天气系统,并对高空急流与副急流进行了动能收支诊断,研究发现:2021年“21·7”河南特大暴雨呈现出显著的阶段性特征,在郑州极端小时降水出现的时段内,强降水主要出现在河南北部的山区及山区的迎风坡周边,受地形响显著。位于河南上空,对流层高层的高压脊、对流层中层的低压倒槽以及对流层低层的水平切变线与中尺度对流涡旋是引发郑州极端小时降水的关键天气系统。处于南亚高压东北部的高空急流与副急流通过引发强冷平流使得位于陕西上空的对流层高层短波槽快速发展,该槽的斜压发展使得其槽前的暖平流显著增强,从而导致河南上空对流层高层的高压脊迅速发展并维持强高空辐散条件,这为郑州极端小时降水的出现提供了极为有利的背景环流条件。南亚高压东北部的高空急流与副急流呈现出显著的水平分布不均特征,其中,风速增强趋势与冷平流强度均在上层急流分岔点(1区)达到极大值,这为陕西上空对流层高层短波槽的快速增强提供了最有利的条件。动能收支表明,南亚高压东北部偏西风的水平动能输送是本区域内高空急流与副急流发展/维持的最有利因子,其动能主要来源于南亚高压北部边缘的高空急流区;在此阶段内,气压梯度力主要做负功,是最不利于高空急流与副急流发展/维持的因子。

The hourly precipitation data provided by the China Meteorological Administration,and the hourly 0.25°(latitude)×0.25°(longitude)reanalysis data provided by the European Centre for Medium-Range Weather Forecasts(ECMWF)were used to investigate the key weather systems that generated the extreme hourly precipitation in Zhengzhou,Henan Province("21·7"torrential rainfall event during 17-22 Jul 2021),and to diagnose the kinetic energy budget of the Upper-Level Jet(ULJ)and sub jet.It was found that,the"21·7"torrential rainfall event in Zhengzhou showed significant phased characteristics.The heavy rainfall mainly occurred in the mountainous areas in the north of Henan during the period of the extreme hourly precipitation in Zhengzhou and around the windward slope of the mountainous areas,which were notably affected by the terrain features.Located over Henan Province,the high-pressure ridge in the upper troposphere,the low-pressure trough in the middle troposphere,the horizontal shear line and the mesoscale convective vortex in the lower troposphere were the key weather systems that caused the extreme hourly precipitation in Zhengzhou.The high-level jet and sub-jet in the northeast of the South Asia high(SAH)caused the rapid development of the upper-tropospheric short-wave trough over Shaanxi Province through the strong cold advection.The baroclinic development of the shortwave trough made the warm advection in its front significantly enhanced,which led to the rapid development of the high-pressure ridge in the upper troposphere over Henan Province.This maintained the strong high-level divergence,which provided a very favorable background circulation condition for the occurrence of extreme hourly precipitation in Zhengzhou.The ULJ and sub-jet in the northeast of the SAH showed significant horizontal unevenness.Among them,the wind speed enhancement trend and the strength of the cold advection both reach maximum values at the bifurcation point of the ULJ(Region 1).This provides the most favorable conditions for the rapid intensification of the upper tropospheric shortwave trough over Shaanxi.The kinetic energy budget showed that the horizontal kinetic energy transport by the westerly wind in the northeast of the SAH acted as the most favorable factor for the development/maintenance of the ULJ and sub-jet in this region,with the kinetic energy mainly come from the ULJ area on the northern edge of the SAH.In this stage,the pressure gradient force mainly did negative work,which was the most unfavorable factor for the development/maintenance of the upper jet and sub jet.