一次回流与倒槽共同作用产生的暴雪天气分析

对2006年1月18—19日山西持续暴雪天气进行了分析,发现这次暴雪过程不同于以往:(1)高空极涡稳定,强度较强,极锋位置偏北,沿极涡外围极锋锋区上分裂的短波小槽,与南支槽同相叠置,使得南支槽发展加深,暴雪发生在此期间。(2)地面图上,不仅形成回流形势,而且河套倒槽向北发展旺盛,倒槽前的暖湿空气与东南气流相遇,两支气流耦合加强,与北方冷空气在山西中南部强烈交汇,使得山西中南部出现了暴雪天气,这种回流形势与倒槽同时强烈发展的情况并不多见。(3)深厚的湿层和强烈的水汽辐合为暴雪的产生提供了充足的水汽条件,暴雪中心就位于中低层两条水汽通量轴线交汇的南侧。(4)高层辐散、低层辐合的垂直配置以及暴雪区上空强烈的上升运动和低层露点锋的持续抬升作用,触发中层高不稳定能量的连续释放,是造成连续暴雪的重要机制,而低空、超低空急流的存在,不仅为暴雪提供了水汽来源和热量输送,而且使得重力波不稳定发展,加强了抬升运动。(5)暴雪出现在500hPa正涡度平流中心右前方,暴雪出现12小时后,正涡度平流中心强度迅速增强,对应暴雪出现一个增幅期。

Analysis of a Snow Storm Caused by Reflux and Invert Trough

A successive snow storm appeared on January 18 to 19, 2006 is analyzed. It shows that this case is different from the samples in the past:(1)The polar vortex at high level is stable and its intensity is large, polar front located at more north than the normal. The short wave trough split from the polar front overlapped with the south trough and made it develop and deepen. At that time, the snow storm occurred. (2) On the surface, reflux in the southeast and invert trough near the Hetao area jointed together and met with cold air from the north and caused the snow storm. (3)The deep moisture layer and the strong water vapor convergence together offered plentiful water for the snow storm. The center of the snow storm located at the south of two water vapor flux axes at low and mid-level separately. (4) The vertical allocation of the divergence at upper and convergence at low level,the strong ascending motion and dew point front continually lifting action triggered greatly convective and unstable energy to release at the mid-level and it is an important mechanism of causing successive snow storm. But LLJ and super-LLJ can not only offer source of water vapor and transportation of energy but also make gravity wave develop unstably, and that is another important triggering mechanism of snow storm. (5) The snow storm appeared at the right and before maximal advection center of the vortex at 500hPa. After 12 hours, the intensity of the positive vortex advection center increased rapidly when there is an increasing rainfall.