一次由河套倒槽影响产生的华北大雪天气分析

利用实况资料和NCEP FNL 1°×1°资料,对2012年12月13日华北大雪天气进行了分析。结果表明,此次降雪过程发生在高空环流较平直的形势下,西风带低槽东移,引导地面冷空气从西北路侵入地面暖倒槽中,与暖湿气流交汇而产生降雪的;深厚的湿层和强烈的水汽辐合为此次大到暴雪提供了充分的水汽条件,暴雪中心位于低层2个水汽通量轴线交汇的南侧;高空副热带西风急流的动量下传是低空偏南急流形成的重要原因,低空西南急流和东南急流的耦合加强,不仅为此次大雪提供了水汽和热量输送,还加强了抬升运动;高层辐散、低层辐合的垂直配置以及暴雪区上空深厚而强烈的上升运动,是强降雪出现的动力条件。

Analysis of A Heavy Snow Caused by Hetao Invert Trough

By using live data and NCEP FNL 1°×1°data, a heavy snow appeared on Dec. 13th, 2012 was analyzed. The resuhs showed that the heavy snow occurred under the situation of straight upper air circulation, westerly low trough eastward, the cold air inversed from the north- west into warm surface inverted trough, and intersected with warm humid air to produce the heavy snow. The deep moisture layer and the strong water vapor convergence together offered plentiful water for the heavy snow. The momentum of the downlink of high altitude subtropical westly jet formed low-level jet. LLJ offered source of water vapor and transportation of energy for the heavy snow. The vertical allocation of the divergence at upper and convergence at low level and the strong ascending motion triggered greatly convective and unstable energy to release at the mid-level and it is an important mechanism of causing short-time heavy snow.