2005年12月威海连续性暴雪的气候背景

利用1966—2005年NCEP/NCAR再分析资料和威海冬季降雪资料,对威海冬季降雪的时空分布特征以及2005年12月威海连续性暴雪的气候背景进行分析。结果表明：威海冬季降雪量呈明显的北多南少分布;12月降雪量和暴雪日数明显多于其他月份。威海市2005年12月的气候特征与威海12月降雪偏多年的气候特征非常相似,表现为东北亚大气环流经向型,中国东北、黄渤海到日本海一带500 hPa位势高度距平和850 hPa温度距平均为显著的负值中心,1000 hPa风场距平为气旋性弯曲;2005年12月的要素距平明显大于降雪偏多年。此外,2005年11月下旬黄渤海海温较常年显著偏高,为大气提供了充足能量,并造成边界层大气极不稳定;山东半岛地形抬升及其北岸的海陆风与环境风辐合,直接导致不稳定能量释放而形成威海连续性暴雪。

Climate Background of Heavy Snow in Weihai City in December 2005

Based on the observed winter snowfall data of Weihai, Shandong Province and NCEP/NCAR reanalysis data during 1966-2005, this paper studies the spatial and temporal distributions of winter snowfall, and the climate background of persistence snowstorm event in Weihai City in December 2005. The results reveal that the winter snowfall is excessive in North and few in South Weihai City, and the snowfall and the day numbers of snowstorm in December are significantly more than those in other months. The climate background in December 2005 is closely similar to that in the more snowfall years of Weihai in December. In the more snowfall years, the meridional circulation lies in northeast Asia with obvious negative centers of 500 hPa height and 850 hPa temperature anomalies locating in Northeast China, Yellow Sea, and sea areas from Bohai Sea to Japan Sea, where there are cyclonic wind anomalies at 1 000 hPa. In the above mentioned areas, the element anomalies in December 2005 are much more robust than those in heavy snowfall years. Moreover, Yellow Sea and Bohai Sea in the last ten-day period of November 2005 is much warmer than the normal, which provides sufficient energy for the atmosphere and results in the instability of atmospheric boundary layer. The terrain uplifting in Shandong Peninsula and the convergence of land-sea breeze and environmental wind in the northern coast directly result in the unstable energy release and the continuous heavy snowfall in Weihai city.