一次东北南部特大暴雪的动力机制分析

The dynamical mechanism analysis of an extraordinary snowstorm over the south of Northeast

应用常规观测资料和NCEP／NCAR再分析资料，分析了2007年3月3-4日东北南部特大暴雪的动力机制，结果表明：850hPa低涡切变线附近对应着强降雪中心，其辐合抬升作用最明显，是本次过程的主要影响系统和成功预报的关键；涡度变率更能准确反映出暴雪切变线生成、发展的物理机制，且对于强降雪中心的位置和强度变化具有一定的预报意义；在涡度变率的各影响项中，700～900hPa正涡度区的强辐合项是正涡度倾向的主要强迫源，低层涡度增加，在强上升运动的作用下向上输送，使系统发展，从动力机制上进一步说明本次过程中主要影响系统的作用；涡度变率中绝对涡度平流项与各层高空槽移动或强度变化有关，反映了暴雪过程中各高度影响系统的垂直结构变化；而扭转项在低层一直产生负贡献，说明上升运动在水平方向的不均匀形成负涡度倾向，不利于系统的发展。

Based on regular observational data and NCEP / NCAR reanalysis data,the dynamical mechanism of an extraordinary snowstorm during 3—4 March 2007 over the south of Northeast China was analyzed. The results showed that the region around the shear line at 850 h Pa,which played a significant role in convergence and lifting,corresponded to the center of the heavy snow and it was also the main influencing system and the key factor for the successful forecast of the event. Vorticity variability could not only reflect the physical mechanism of the formation and development of the snowstorm shear,but also predict the position and intensity of the heavy snowstorm. Among all the factors affecting vorticity,the strong convergence terms in positive voritcity regions at 700 h Pa to 900 h Pa was the main forcing source of positive voritcity tendency. When voritcity on lower level increased,it transported upwards and made the system develop,which illustrated the function of the main system dynamically. The absolute vorticity advection was related with the movement of trough and its intensity varieties on different levels,which reflected vertical changes of the influencing system on different levels during the snowstorm. The twisting term played a negative role on low level,which meant that the upwards movement distributed asymmetrically in horizontal direction which formed negative vorticity and it negatively affected the development of the snowstorm system.