一次华北破纪录暴雪成因的分析研究

采用常规资料和多种非常规资料(卫星图像、多普勒雷达资料及地面自动站资料等)对2009年11月华北地区的大暴雪过程进行了诊断分析,并计算了锋生函数、能量收支、水汽输送等物理量,以探讨暴雪形成的原因。取得以下结果:(1)暴雪过程中出现了回流天气(且伴有"扰动"),这有利于水汽输送和水平辐合的加强,同时,冷高压的南侧低层有"倒槽"存在,对暴雪的形成有重要的作用。(2)雷达观测资料表明,石家庄西南始终有一条辐合线稳定维持,沿此辐合线不断有中尺度云团反复发展,而引起罕见暴雪。(3)由太原及邢台的探空曲线可知,有明显的锋面及逆温区存在,利于不稳定能量的积累。因不存在"暖鼻",故只是降雪无冻雨发生。(4)在上述资料分析和多项动力学诊断的基础上,提出了一类华北暴雪的物理模型。

Analysis of a Record Heavy Snowfall Event in North China

In this paper, the authors discussed a record heavy snowfall event that occurred in North China in November of 2009. The conventional and unconventional data including satellite images and Doppler radar and automatic weather station (AWS) observations were utilized. The related physical quantities including the frontogenesis function, the kinetic energy budget and moisture flux were computed and the formation mechanism for the heavy snowfall was investigated. Major conclusions are as follows:(1) The returning flow accompanied with disturbances intensified the moisture transport and horizontal convergence in North China. The "inverted trough" to the south of the cold high pressure in the lower troposphere also played an important role in the formation of the heavy snowfall. (2) Radar data revealed clearly that a convergence zone maintained stably to the southwest of Shijiazhuang City, where convective cloud clusters developed continuously and directly led to the formation of heavy snowfall. (3) In the T-lnp diagrams of sounding data at Taiyuan and Xingtai, the frontal zone with the inversion layer could be seen clearly, which was favorable for the accumulation of unstable energy. However, the "warm nose" did not exist, which explains why only the snowfall occurred and there existed no freezing rain. (4) Based on the above discussions, a conceptual model for North China heavy snowfall was proposed.