双月刊

ISSN 1006-9895

CN 11-1768/O4

中国西南部一次东移型暴雨中涡旋发展的多尺度地形影响研究
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1.安徽农业大学;2.中国科学院大气物理研究所

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中国科学院战略性先导科技专项XDA23090101;国家自然科学基金资助项目41875079, 91937301, 41575064


Multi-scale topographical attribution detection for the development of an eastward rainstorm vortex in southwest ChinaLi Xiang1,2, Yang Shuai2, Yang Shuyun1
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Institute of Atmospheric Physics, Chinese Academy of Sciences

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    摘要:

    由观测分析和数值模拟,发现2019年8月5-6日中国西南部的东传型致灾暴雨事件中存在三涡(南北双高原涡、西南涡)相继发展并导致暴雨加强和传播的现象。借助数值试验,研究了多尺度地形因子(青藏高原、横断山脉和四川盆地三大地形)各自对涡旋演变的作用。结果表明,横断山脉对西南涡的形成起关键作用,四川盆地影响着西南涡的位置和强度。对于高原涡(这里指南侧高原涡)的传播,四川盆地只影响涡旋强度演变,但不会改变高原涡的传播路径。一旦横断山脉被移除,高原涡的传播现象随之消失。进一步分析青藏高原和四川盆地交界处的陡峭地形坡度改变对涡旋发展的影响,发现坡度越陡,高原涡传播速度越快,且盆地内二涡合并后的西南涡强度越强。最后借助于倾斜涡度发展理论,解释了不同坡度对涡旋强度演变的影响:随着坡度变陡,倾斜涡度发展系数CD剧烈减小;陡坡时沿涡旋下滑路径快速减小的CD对垂直涡度局地倾向的强迫作用,加剧了涡旋的快速加强。

    Abstract:

    Based on observation analyses and numerical simulation, we reveal that three vortexes, north Plateau Vortex (PLV1), south Plateau Vortex (PLV2), Southwest Vortex (SWV), develop successively during the disaster-causing rainstorm event in Southwest China from 5 to 6 August 2019, which lead to the intensification and eastward propagation of the rainstorm. By utilizing of numerical experiments, the effects of multi-scale topographic factors (Tibetan Plateau, Hengduan Cordillera and Sichuan Basin, denoted as TP, HC and SB) on the evolution of vortexes are studied. The results show that, HC plays a key role in the formation of the SWV, while SB influences the location and intensity of SWV. As for the propagation of Plateau vortex (PLV2 herein), SB only affects the vortex intensity, but does not change the propagation path of PLV2. Once HC is removed, the propagation of the Plateau Vortex disappears. The influence of slope change of the steep terrain at the boundary between TP and SB on the development of vortex is further analyzed. It shows that the steeper the slope is, the faster the propagation speed of the Plateau vortex is, and the stronger the SWV is after the two vortexes (PLV2 and SWV) merge. Finally, the impact of varied slopes on the evolution of vortex intensity is explained based on the theory of slantwise vorticity development. As the slope becomes steeper, the coefficient of slantwise vorticity development (CD) decreases sharply. In the case of steep slope, the forcing effect of rapidly-decreasing CD along the track of vortex glide on the local tendency of vertical vorticity contributes to the rapid intensification of the vortex.

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  • 收稿日期:2021-04-25
  • 最后修改日期:2021-06-03
  • 录用日期:2021-06-10
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