甘肃白银市大到暴雪大气环流特征分析

Analysis of Atmospheric Circulation Features of Heavy Snow in Baiyin City of Gansu Province

为了提高暴雪天气的预报预警能力,利用NCEP/NCAR再分析资料,对白银市1961—2016年大到暴雪天气过程进行了分析。结果表明:(1)白银市大到暴雪多发生在初春和秋末,其空间分布具有南多北少的特征。(2)白银市形成大到暴雪天气的环流形势可归纳为4类:横槽型、北脊南槽型、南北槽叠加型和高原槽型。(3)各类分型在中低纬都表现为南支槽建立、高原槽发展,起到暖湿气流的输送作用;高原东北部低涡或切变线发展,加强了大气的上升运动;高原东北部低压倒槽的发展,增强了该区的大气的不稳定度,使得上升运动加强。(4)各分型的不同点主要是中高纬地区天气系统的不同,即从高原以北东移的西风槽脊的类型和位置的不同,它们主要起到冷空气的输送作用。(5)白银市形成大到暴雪天气的水汽主要来自于南支槽和高原槽的输送,700 hPa比湿≥3 g/kg是产生大到暴雪的必要条件。

In order to improve the ability of blizzard weather forecast and early warning,this paper analyzes the blizzard weather process data from 1961 to 2016 in Baiyin City by using NCEP/NCAR global reanalysis data.The conclusions are as follows(a)heavy snow in Baiyin occur mostly in the early spring and the late autumn,and their spatial distribution characteristic is less in the North and more in the South.(b)The circulation patterns causing heavy snow in Baiyin can be classified into four categories,which are transversal trough type,north ridge south through type,north-south trough superposition type and plateau trough type(c)Each sub-types are expressed as established in southern branch trough and developed in plateau trough,which are able to transport warm-wet air.The low vortex or shear line development in the northeastern part of the plateau enhances the ascending motion of the atmosphere;the development of the low pressure inverted trough in the northeastern part of the Tibetan Plateau enhanced the instability of the atmosphere in this area to strengthen the ascending motion.(d)The main difference among these patterns is the different weather systems in the mid-high latitudes,which specifically focus on different types and locations between westerly troughs and ridges moving eastward on the north side of the Tibetan Plateau,mianly for cold air transportation.(e)The water vaper formed heavy snow in Baiyin is mainly transported through both the southern trough and the plateau trough.The necessary condition of heavy snow in Baiyin is specific humidity≥3 g/kg at 700 hPa.