北疆暴雪过程的湿位涡诊断

Diagnosis of Moist Potential Vorticity of a Snowstorm Process in Northern Xinjiang

利用NCEP1°×1°再分析资料,对2009年3月19—20日北疆沿天山一带一次暴雪天气过程进行诊断分析,着重探讨了湿位涡诊断在新疆暴雪预报中的应用。分析表明:暴雪的水汽输送有3个源地,低层负散度、向北倾斜的涡度"上负下正"分布、等θe线的陡立密集带、垂直速度负值区与暴雪落区均有较好的对应关系。暴雪主要发生在MPV1>0、MPV2绝对值迅速增加且等值线密集分布的区域。MPV1下传增大,大气对流不稳定能量释放,低层MPV2绝对值增大,大气湿斜压性增强,下滑倾斜涡度增长是暴雪形成的重要原因。

Using the NCEP 1°×1° reanalysis data, a snowstorm in northern Xinjiang from March 19th to 20th in 2009 was analyzed and the application of wet potential vorticity was emphazed. The results showed as follows. There were 3 vapor sources of the snowstorm. The area of snowstorm were corresponded to the negative divergence in lower layers, inclining northward vorticity that was negative in the upper air and positive below, intensive belt of equivalent potential temperature that rises steeply, and negative vertical velocity area. The snowstorm occurred in the area where positive MPV 1 amplified distinctly, and the absolute value increased rapidly and isolines of MPV2 were intensive. The important causes for the snowstorm formation included that MPV1 transfered down increasingly, atmosphere convective instability energy released,the absolute value of MPV2 at low level magnified and atmospheric wet baroclinicity enhanced and the development of down-sliding slantwise vorticity.