渭河流域一次连续降雪天气过程综合分析

Comprehensive Analysis on a Continuous Snowfall Process in Weihe Valley

利用NCEP/NCAR日平均再分析资料对2008年1月出现在渭河流域的一次连续降雪天气过程进行了分析,结果表明,近地层存在持续的强东风,为连续降雪起到了冷垫作用;各种有利条件的相互作用,造成该区持续强劲的垂直上升运动,甚至形成类似于夏季对流性天气中出现的次级环流,是这次连续降雪过程的主要抬升机制。高空西风急流位置的迅速抬高和突然下降对降雪的开始和结束有一定的指示意义;中雪以上的降雪发生前,高层比湿先增强,随后低层比湿迅速增大,渭河流域700hPa比湿值≥3 g.kg-1的湿舌形成之后,强降雪开始。

The continuous snowfall process happened in Weihe basin in January 2008 is analyzed and discussed using the NCEP/NCAR daily average reanalysis data.Results show that there is sustained and strong east wind on the surface layer,which play the cold cushion action for continuous snowfall weather.The interaction of all kinds of advantage condition resulted in the sustained and strong vertical ascending motion,even it formed to be similar to the secondary circulation happened in the convective weather of summer,which is the main lifting mechanism in the snowfall process.The rapidly lifting and suddenly descending of westerly jet position have certain indication significance for the starting and ending of snowfall.Before the snowfall over moderate snow occurring the upper specific humidity firstly enhance,then the lower one rapidly increase.After the moisture tongue of 700 hPa specific humidity more than 3 g·kg-1 in Weihe basin has been formed,the severe snowfall process begins.