2011年1月湖南罕见持续性暴雪天气成因分析

Cause analysis of rare continuous blizzard occurring in January 2011 in Hunan province

应用常规观测资料和NCEP再分析资料,对2011年1月湖南发生的罕见大范围持续性暴雪天气过程进行了详细分析。结果表明:乌拉尔山阻塞高压和孟加拉湾南支槽稳定维持,"南低北高"环流形势有利于冷暖气流在长江中下游地区一带汇合,是持续性暴雪发生的大尺度环流背景;700 hPa西南急流的建立和加强为暴雪区带来源源不断的水汽供应和不稳定能量,持续而强盛的水汽输送和水汽辐合对暴雪维持和加强至关重要;青藏高原有两次明显的正涡度向东传播至我国东部地区,正涡度东传有利于垂直上升运动维持和加强;暴雪期间湖南上空维持较强的锋生区,准静止锋稳定少动,锋区强度逐渐增强,其最强阶段与暴雪最强阶段一致,而高空急流和锋面的耦合加强了湖南区域的上升运动,是暴雪天气持续的主要原因;锋前干冷空气在对流层中层形成的干层加强了暴雪过程的对流性不稳定,而锋后干冷空气作为"冷垫"锲入暖湿气流下方,促进锋生和暖湿空气的抬升和凝结,是不稳定能量释放的触发机制。

Rare and continuous blizzard occurred in January 2011 in Hunan province was analyzed comprehensively by using conventional observational data and NCEP reanalysis data. Conclusions are drawn that stability and continuance of Ural Mountains blocking high and south branch trough in the Bay of Bengal made a circulation characterized by ＂low in south and high in north＂. It was favorable for cold airflow and warm airflow to join up in the middle and lower reaches of the Yangtze River providing the beneficial large-scale circulation background for the occurrence of continuous blizzard. The establishment and reinforcement of southwest jet at 700 hPa supplied mass of water vapor and un- stable energy to blizzard region, while continuous and powerful water vapor transport and convergence played a crucial role in the continuance and reinforcement of blizzard. From Tibetan Plateau to eastern China there were two obvious positive vorticities spread eastward orderly, which is propitious to the continuance and reinforcement of upward motion. During the blizzard, stronger frontogenesis maintained, quasi-stationary frortt was stable, as ,sell as front zone strengthened gradually. The strongest stage of the front zone was consistent with the strongest stage of the blizzard, and the coupling of upper-level jet and front strengthened the upward motion over Hunan. This is the main reason which led to the continuance of blizzard. The dry layer originated by the prefrontal dry and cold air in the middle troposphere strengthened convective instabili- ty of the blizzard, while the post-frontal dry and cold air playing as a cold air cushion wedged into the space bellow warm and humid airflow to cause the frontogenesis and both the uplift and condensation of warm and humid air, which triggered the release of instable energy.