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2023年7月一次华北极端暴雨的多尺度特征

Multi-scale characteristics of an extreme rainstorm in North China on July 2023

  • 摘要: 利用ERA5 0.25°×0.25°再分析资料和日本气象厅GSMaP(Global Satellite Mapping of Precipitation project) 0.1°×0.1°逐小时降水数据分析了2023年7月华北的一次极端暴雨过程的多尺度特征。结果表明,本次华北极端暴雨是在孟加拉湾季风涡旋、台风“杜苏芮”残涡、台风“卡努”、高低空急流、阻塞高压和地形等要素共同作用下形成。这种多尺度天气系统的配置不同于以往的任何一次极端暴雨过程,其中孟加拉湾季风和台风“卡努”为降水的持续发生提供了水汽输送通道,位于华北北侧的阻塞高压使得来自低纬度的水汽持续在太行山以东聚集,使“杜苏芮”残涡获得水汽并维持在太行山南麓,而“杜苏芮”残涡与其北侧的阻塞高压和东侧的西北太平洋副热带高压之间水平位势梯度增大促进了低空急流的发展。在850hPa低空急流与200hPa高空急流的耦合作用下不断地有中尺度对流云团在太行山迎风坡生成,当华北地区地面风向与太行山地形近乎垂直时地形造成的强迫抬升运动更加显著,这也促进中尺度对流云团的进一步组织和发展,最终形成短时强降水。强降水发生的第一阶段大气层结在垂直方向上是对流稳定,但是加强的边界层低空急流促进了迎风坡气流发生倾斜上升运动,激发了条件性对称不稳定能量释放,产生强烈降水;第二阶段的强降水主要发生在暖区,大气层结表现为垂直对流不稳定,此阶段由地形动力强迫触发降水。

     

    Abstract: The multi-scale characteristics of an extreme rainstorm in North China on July 2023 were studied using ERA5 reanalysis data with the spatial resolution of 0.25° × 0.25° and JMA GSMaP precipitation data with the spatial resolution of 0.1° × 0.1°. Results showed that the extreme rainfall episode in North China was formed under the combined effect of monsoon vortex in the Bay of Bengal, remnant of Typhoon Doksuri, Typhoon Khanun, upper- and low-level jet, high blocking and terrain elevations. The configuration of multi-scale weather systems was unlike any previous extreme rainstorm process. The Bay of Bengal monsoon and Typhoon Khanun provided favorable conditions for transportation of water vapor during the continuation of precipitation. A high blocking to the north of North China caused the accumulation of water vapor from low latitudes to gather at east of the Taihang Mountains. The remnant vortex of Doksuri obtained water vapor and was situated at the southern foothills of the Taihang Mountains. The horizontal potential gradient formed by this remnant vortex, along with the blocking high pressure to its north and the western North Pacific subtropical high to its east, promoted the development and intensification of a low-level jet. The coupling of 850 hPa low-level jet and 200 hPa high-level jet continuously generated mesoscale convective clouds on the windward slopes of the Taihang Mountains. When ground winds in North China were nearly perpendicular to topography, pronounced forced lifting motion due to topography further organized and developed mesoscale convective clouds, resulting in short-term heavy precipitation. The first stage of intense precipitation occurred when atmospheric stratification was vertically convectively stable. However, intensified boundary layer low-level jet promoted inclined upward flow over windward slopes, triggering release of conditionally symmetric instability energy and leading to heavy precipitation. The second stage mainly occurred in warm sectors with atmospheric stratification showing vertical convective instability triggered by terrain-induced dynamical forcing.

     

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