山东半岛一次持续性强冷流降雪过程的成因分析

利用NCEP/NCAR逐日6 h再分析资料和观测资料,诊断分析了2005年12月3～21日山东半岛北部沿海地区发生的罕见持续性强降雪过程.结果表明: 降雪以西北气流下的冷流降雪为主,具有典型冷流降雪分布特征;有利的大气环流形势造成强冷空气频繁,经过渤海暖海面时产生较大海气温差,是降雪持续时间长、强度大的直接原因;一定的海气温差是冷流降雪的重要指标,产生冷流降雪时山东北部近海海域的海气温差常在22K以上;冷流暴雪产生在高能舌、对流层低层辐合、中层辐散的上升运动区,上升运动层浅薄;水汽来源于渤海,水汽辐合层位于超低层(925 hPa高度以下);对流层中低层的垂直速度、散度场、涡度场的动力耦合结构配置有利于暴雪的形成和维持;特殊的低山丘陵地形强迫抬升是冷流降雪的触发机制,对暴雪的产生起到增幅作用.

A Diagnostic Analyses on Peculiar Persistent Cold Airflow Snowstorm Process in Shandong Peninsula

Using the NCEP/NCAR day-to-day 6 h reanalysis data and observational data,the peculiar persistent cold airflow snowstorm occurring off northern coast of Shandong Peninsula from 3 to 22 December 2005 is diagonally studied.The results show that the snowstorm occurred when northwest airflow prevailed and the snow distributing is of typical cold airflow snowstorm character.Frequently strong cold air causea great sea-air difference,which is the main reason to induce long term severe snowstorm.Sea-air temperature difference more than 22K is the essential condition and remarkable cold front is found in 850 hPa when cold airflow snow occurring.Snowstorm occurred in the high energy belt,updraft area with convergence in low troposphere and divergence in middle troposphere.Vapour from Bohai converges under the level of 925 hPa.Updraft layer is much more lower than summer heavy rain.The act of forming couples among vertical velocity,divergence and vorticity field in low and medial troposphere is helpful to the form of snowstorm.The force lift of special hill topography is the trigger of cold airflow snow and increase the snowstorm.