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南亚高压与偏北风急流出口区的暴雨生成机制
ANALYSIS OF RELATION OF SOUTH ASIA HIGH AND RAINSTORM CAUSED BY NORTHWESTERLY UPPER-LEVEL JET
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摘要: 利用MM4中尺度模式，模拟了1998年7月21日08：00~22日08：00(北京时)，一次西北风急流的暴雨过程。分析发现，西北风高空急流与南亚高压环流形成的辐散辐合场导致一对中尺度正反环流的生成，使暴雨得以维持与加强。在暴雨区北部，中高层条件性对称不稳定可使下沉运动加速，对北支环流的维持起关键作用；雨区南部，南支环流圈的维持与高层北风中心的加强有关。北支环流圈的加强以及动量下传使暴雨区北部低层的北风分量维持。该北风分量与雨区南部环流的南风分量形成低层辐合。Abstract: Using MM4 model, the process of rainstorm is molded in the period from 08:00 BLT July 21 to 08:00 BLT July 22, 1998. It is found that the convergence and divergence field of the South Asia High and the northwesterly upper-level jet form a couple of mesoscale direct circulation and counter-circulation. The circulation pattern keeps the rainfall maintaining and strengthening. The sinking of the high potential vorticity is related to the lower vortex and the rainfall increasing. The conditional convective instability in the later period is more obvious for the effect of rainstorm than conditional symmetric instability.
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