孟湾风暴影响高原暴雪的个例分析:基于倾斜涡度发展的研究

A Case Study of Snowstorm in Tibetan Plateau Induced by Bay of Bengal Storm:Based on the theory of Slantwise Vorticity Development

基于湿位涡(MPV)诊断分析和倾斜涡度发展(SVD)理论,研究了2007年11月一次孟加拉湾热带风暴北上造成青藏高原暴雪的天气事件。结果表明:热带风暴螺旋云系移动至高原东南部受陡峭地形抬升与高层北侧下滑的干冷空气(MPV1正值带)相交汇是导致这次天气过程的重要原因。由于等熵面密集且明显倾斜,在降雪区上空附近大气弱稳定区,负的MPV2对总湿位涡MPV的贡献超过了MPV1,SVD得到较大增长,同时使得MPV<0,导致条件性对称不稳定的产生,有利于倾斜涡度的发展。条件性对称不稳定机制是这次暴雪发生、发展的一种可能的重要机制。

Based on the diagnosis of moist potential vorticity（MPV） and the theory of slantwise vorticity development（SVD）,a case study of snowstorm in the Tibetan Plateau induced mainly by Bay of Bengal storm in November 2007 was analyzed.The results show that the interaction of the storm′s spiral cloud band and the down-sliding dry cold air（positive MPV-1 band） over the steep southern fringe of the plateau is the main reason for this synoptic process.Owing to the dense and obvious slantwise isentropic surface,the contribution of negative MPV-2 to moist potential vorticity（MPV） is more than MPV-1 over the snowfall area where atmosphere is weak stable.It further leads to the sharp growth of SVD.Moreover,negative MPV makes a favorable background of the generation of conditional symmetrical instability.The conditional symmetrical instability is beneficial to the development of slantwise vorticity,and it is a possible important mechanism for this snowstorm.