2008年1月宁夏北部低温连阴雪天气成因及特征分析

为更好地开展短期气候预测业务，从气候角度分析了该次灾害的天气成因，并对2008-01-19——21日的连阴雪天气的环流形势和物理量场进行了分析．结果表明，500hPa极涡位置较常年同期偏南，贝加尔湖高压脊稳定，极地冷空气不断沿贝加尔湖脊前西北气流南下影响宁夏，是造成宁夏及其北部持续低温天气的主要原因．乌拉尔山地区位势高度场异常偏高，中亚至蒙古国西部地区偏低，非常有利于冷空气不断分裂南下，为石嘴山市出现连阴雪天气提供了冷空气条件；西太平洋副热带高压异常偏北，为宁夏北部输送了暖湿空气．500hPa中高纬度稳定的阻塞形势、中空700hPa稳定的水汽输送、地面倒槽和回流提供了稳定的暖湿气流，是19—21日连阴雪天气持续时间长的主要原因；湿层不够深厚，700hPa未形成低空急流和动力机制不够强，是该次连阴雪天气降雪量未达到历史同期最高值的主要原因．

Analysis of synoptic cause and the features in north region of Ningxia on January 2008

In order to better carry out short-term climate prediction business, the causes of weather disasters are analyzed with the view of climate.In the second part of this paper, the possible climatic causes and the long snowfall during 19-21 January are analyzed. Results show that, in that period, the 500hPa Arctic polar vortex leaned to southward,Baikal Lake ridge was stable, and Ningxia was influenced by the cold air mass from the polar region, leads to the severe cold surge in north region of Ningxia. The geo-potential height over the Ural was abnormally high while the counterpart over the Middle Asia and the Mongolia was low. This condition is help for the cold air flowed to south from the high latitudes, and cold weather conditions caused long term raining and snowing days in Shizuishan. In same term, the western Pacific subtropical high located more to northward, which transports the warm and wet moisture to the north of Ningxia. The mostly reason of long lasting snowfall during 19--21 is that the steady blocking situation in high-middle latitudes 500 hPa, the steady water vapor transportation over 700 hPa, the lasting warm and wet current from reflux and invert trough. The important reason that the snowfall was not the maximum in history same period is that the humidity was shallower, the weak dynamical mechanism and the low-level jet stream had not existed.