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太行山精细地形对“23.7”华北极端暴雨特征影响的观测分析

Observational analysis of Mount Taihang’s Orographic Effects on the “23.7” Extreme Precipitation Event in North China

  • 摘要: 本文基于高分辨率多源观测资料,分析了太行山精细地形对“23.7”华北极端降水落区、强度、降水极值中心及对流发展过程的影响。“23.7”华北降水过程是超强台风“杜苏芮”残余环流北上导致的长历时、大范围、高强度的极端降水事件,站点最大累积降水量1003.4 mm,特大暴雨落区、突破日降水量极值站点均分布在太行山东侧迎风坡。累积降水量峰值出现在太行山迎风坡400 m高度左右,600 mm以上的降水中心多位于太行山东侧中小尺度山体构成的喇叭口地形内侧。分析表明,在北方大陆高压、西太平洋副热带高压以及太行山-山西高原地形的共同阻碍作用下,7月29日起台风“杜苏芮”残涡移动缓慢,京津冀地区长时间受涡旋北侧倒槽辐合区和地形辐合区控制,在系统性抬升以及持续水汽输送等机制下形成长历时强降水;台风残涡环流与高压坝之间形成了天气尺度东风低空急流,富含水汽的偏东气流从平原地区边界层沿太行山地形爬升,水汽通量辐合中心、上升运动中心位置均出现在太行山半山坡950-925 hPa附近,有利于在半山坡高度处形成降水峰值。太行山精细地形对MCS(Mesoscale Convective System)发生发展产生了重要影响,7月29日夜间在涡旋倒槽系统影响下,向太行山迎风坡爬升的MCS显著增强,山前东北风气流在中尺度喇叭口地形内侧形成气旋性辐合中心,并导致持续性强降水;在MCS东侧冷池边界附近,对流初生和组织化导致山前平原地区出现短时暴雨。7月30日夜间,在边界层南风急流以及山区地形性涡旋环流组织下,局地发展的中β尺度线状MCS造成超过100 的极端雨强。该研究深化了地形对华北极端降水影响机制的科学认识,并有助于为今后预报决策提供参考依据。

     

    Abstract: Based on high-resolution multi-source observational data, the topographic effects of the Taihang Mountains on intensity, centers and convective development characteristics of the extreme precipitation struck North China was analyzed. This long-lasting, widely impacting extreme precipitation event with high-intensity was primarily caused by the northward movement of the remnant circulation of Super Typhoon Doksuri, with the maximum cumulative precipitation up to 1003.4 mm. And the extreme rainfall area and the recording-broken daily precipitation were distributed on the upwind slope on the eastern side of Taihang Mountain. The peak of the cumulative precipitation occurred at the altitude of about 400 m on the upwind slope, and centers of accumulated precipitation above 600 mm were located on the inner corner of open-valley terrain composed of mesoscale mountains on the eastern side of Taihang Mountain. Due to the blocking effect of the northern continental high, the Western Pacific Subtropical High and the topography of the Taihang Mountains and Shanxi Plateau, the residual vortex of Doksuri moved slowly since July 29. The Beijing-Tianjin-Hebei region has been dominated by convergence induced by the inverted-trough on the north side of the vortex and the topographical blocking, forming synoptic uplifting. Low-level easterly jet formed between the typhoon residual vortex and the high pressure barrier. As a result, water vapor flux climbed from the boundary layer over the plain to the upslope of the Taihang Mountains. The convergence center of water vapor flux and the upward movement occurred near 950-925hPa on the mid-slope, which was conducive to the formation of precipitation peak on the mid-slope. The fine terrain of the Taihang Mountains took significant impact on the occurrence and development of the Mesoscale Convective System (MCS). On the night of July 29, the MCS approaching to the upwind slope was significantly enhanced, and under the northeast wind background in front of the mountain, a convergence center was formed on the inner side of the mesoscale trumpet shaped terrain, leading to sustained heavy precipitation. Because of the boundary organization of the cold pool on the east boundary of MCS, the initiation and development of the new convection led to short-term rainstorm in the piedmont plain. On the night of July 30, under the organization of the southerly boundary jet and the topographic vortex circulation, the locally developed meso-β scale linear MCS caused an extreme rainfall intensity exceeding 100 . This study deepens the scientific understanding of the mechanism of extreme precipitation in North China and helps to provide a reference for future forecasting decisions.

     

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