高原东侧陡峭地形对一次盆地中尺度涡旋及暴雨的数值试验

Simulation of Impact of Steep Terrain on East Side of Qinghai-Xizang Plateau on Mesoscale Vortex and Rain Storm over the Basin

利用MM5中尺度模式，对2003年8月8～10日发生在四川盆地的一次强降水过程进行了数值模拟。分析表明：MM5模式较成功地模拟出2003年8月8～10日发生在高原东侧陡坡地形区域的四川盆地西北部的大暴雨过程。在本次暴雨过程中，中尺度涡旋有利于盆地上空正涡度输送和辐合上升运动的维持，有利于降水的维持和强降水的发生。地形对中尺度涡旋活动的影响主要表现在：复杂陡峭的地形扰动有利于中尺度涡旋的形成。保留真实地形，在青藏高原东部到盆地西部，涡旋活动频繁；降低地形高度和坡度，不仅减少了涡的个数，还减弱了涡的强度，并改变了涡的生成源地以及涡的移动路径；不考虑地形使得青藏高原到四川盆地西部涡旋活动明显减少，且涡移动速度加快；仅降低地形高度而不改变地形坡度，对该地区的涡旋活动无明显的影响；仅保留青藏高原地形，高原地区涡旋活动频繁，无地形地区涡明显减少。数值试验还表明，地形与涡旋的活动及降水的分布密切相关。

The MM5 mesoscale model was used to simulate a heavy rain process taking place in northwestern Sichuan Basin on 8-10 August 2003 and some numerical experiments with different kinds of changed topographies were run. The results of experiment show that the mesoscale vortex is favorable for the transportation of positive vorticity and the maintenance of convergent and ascending motion, as a result, the precipitation maintenance and heavy precipitation occuring; The influence of topography on mesoscale vortex mainly shows that the steep and complex topography is of advantage for the generation of mesoscale vortex. In the control experiments with the real plateau topography, the vortexes are more and active over the Plateau and western Sichuan Basin; when the topography is altered in both height and slope, the numbers of vortexes reduce, the intensity of vortex weakenes, and the sources of vortex and their moving paths shift; when the topography is removed, vortexes are less, moreover, vortexes move faster than usual; if the topography is cut down only in height, vortex activities change little; when only the Plateau exists, vortexes are still active in the Plateau area, but in no-topography area vortexes deceased apparently. The results also reveal that the activity of vortex has something to do with the distribution of rainfall.