青藏高原背风坡地形对西南涡过程影响的数值试验

NUMERICAL STUDY ON THE LEEWARD SIDE OROGRAPHIC EFFECTS OF QINGHAI-XIZANG PLATEAU ON A SOUTHWEST VORTEX PROCESS

在一个有三重水平结构的台风数值模式基础上，发展了一个能考虑青藏高原及其背风坡不同尺度地形的数值模式，用于１９８１年７月１２日２０：００～７月１４日２０：００西南涡个例的数值研究。模式中设计了全地形、１／３地形和无地形三种方案。对比试验结果表明：全地形对西南涡的移动和发展、形状和范围均能较成功地模拟，降低地形或无地形时，模拟则不成功。全地形时急流轴为偏北方向，而在１／３地形或无地形时，急流走向为偏东方向。全地形时大区流场呈现切变辐合型，而没有地形时流场呈大槽型分布，西北冷空气大举南下。全地形时成功地模拟出了降水分布及降水区中心，而降低地形及无地形时的模拟则不成功。

Based on a typhoon numerical model with horizontally threefold structure,a numerical model,in which the Qinghai-Xizang Plateau and its leeward side different scale orographic effects can been considered,is developed to study on a southwest vortex process during the period from 20:00 BST 12 to 20:00 BST 14 July,1981. Comparison of the three numerical experiment results——with real orography,one third orography and without orography——shows:the features of the southwest vortex such as its movement,development,shape and domain,as well as the distribution and centres of its precipitation can be well simulated in the experiment with real orography.however,in other two experiments,it is failed to simulated out these features.Furthermore,the axis of the jet stream takes northward direction in the experiment with real orography,but it takes eastward either in the experiment with one third orography or in that without orography.Instead of appearing the shear-convergence flow pattern in the experiment with real orography,the wind field appears a deep trough pattern in that case without orography,so the massive northwest colder air mass moved southward.