摘要
选取河北省2003年和2004年两次较大的降雪过程,利用常规气象资料和NCEP再分析资料,对它们的环流形势和物理量场作了对比分析。结果表明,500 hPa南北两支槽在110°E附近同位相叠加、地面气压场"北高南低"并在河套地区有倒槽生成是河北出现大(暴)雪的有利形势。低层暖温舌和暖平流的存在为大(暴)雪的形成提供了较好的热力条件。槽前西南气流、低层偏东气流和低空急流都能为产生大(暴)雪带来充足的水汽。高层辐散、低层辐合的水平散度结构和整层为垂直上升气流的分布,加强了上空的抽吸作用,有利较大降雪的发生。而整层是正涡度(正垂直螺旋度)对垂直上升运动最有利。925 hPa和850 hPa温度同时降至0℃以下,且地面气温小于等于1℃是适合降雪的温度条件。
In order to reveal the development mechanisms of heavy snowfall in Hebei Province,two heave snow processes on 14 to 16 March 2003 and 20 to 21 February 2004 are selected.A contrast analysis of their meteorological characteristics is made from aspect of synoptic situation and physical mechanism by means of numerical diagnosis with the NCEP reanalysis data and conventional observation data.The results show that the combination of south and north troughs with identical phase around 110°E at 500 hPa,the allocation of the surface pressure field with high in north and low in south,and the appearance of the ground inverted trough in the Hetao area of NW China,as well as the thermodynamic conditions with warm temperature tongue and warm advection in the lower troposphere,are the favorable large-scale background for the formation of heavy snowfall.There are three important paths of water vapor in the two snow events： from southwest in front of the 500 hPa trough,from east at low level,and from low-level jet.From the cross sections of vorticity,divergence,vertical velocity and vertical helicity,it is found that the vertical distribution of convergence at low level but divergence at upper level and ascending motion in the whole troposphere benefit the forming and maintaining of heavy snowfall,and the distribution of positive vorticity（vertical helicity） in the whole troposphere is most favorable.It is also suggested the temperature descending to below 0 ℃ at both 850 hPa and 925 hPa,meanwhile below 1 ℃ in the surface,is favorable to snowing.The results can be used as reference in the forecasting heavy snowfall.
出处
《气象科技》
北大核心
2010年第3期281-288,共8页
Meteorological Science and Technology
基金
中国气象局新技术推广项目预报员专项(CMATG2007Y05)资助
关键词
大(暴)雪
低空气流
暖平流
垂直螺旋度
heavy snowfall
low-level jet
warm advection
vertical helicity
