冀南大到暴雪天气过程分析

Analysis of the Heavy Snow to Blizzard in Southern Hebei

利用NCEP1°×1°的6h再分析资料和常规气象观测资料,对2001年1月6日冀南大到暴雪天气过程进行了诊断分析,结果表明:冀南地区大到暴雪天气过程的主要影响系统是低层辐合切变线、高空槽、低空和超低空急流;降雪过程中前期为回流降雪,后期为西来槽降雪;冀南暴雪区处于偏南风急流左前方的辐合区内,低空、超低空急流为暴雪提供了源源不断的水汽条件;暴雪过程中存在较为深厚的上升运动,散度的垂直分布形成上下抽吸作用,中低层正涡度的发展尤其是正涡度平流的增强等均为强降雪提供了动力条件;非地转湿Q矢量散度场低层辐合明显,强辐合区与暴雪区有较好的对应关系;低层高能舌的演变可以大致判断强降水出现的时间和位置;由假相当位温垂直方向上的变化可知,冀南地区大到暴雪基本属于稳定性降雪过程。

By using the NCAR/NCEP reanalysis data and meteorological conventional observation, the heavy snow to blizzard occurred in southern Hebei on January 6th 2001 are analyzed. The results showed that the major af- fect system was low-level convergent shear line, upper trough, low and extra low altitude jet flow. The prometaphase was return-flow and the later was west trough. Blizzard region was in the convergence zone of the jet left front and full of sufficient moisture. The deep ascending motion, the pumping action in the divergence and the enhanced positive vorticity advection were the good dynamic condition. The convergence was obvious in low- level divergence fields of the ageostrophic wet Q vector and the strong convergence area had a good correlation with the heavy snow. The time and position of the heavy snow can be included from the evolution of the low energy tongue. From the changes of the potential pseudo-equivalent temperature in the vertical direction we can see that the heavy snow and Snow-storm in the Southern Hebei was belongs to the stability snowfall.