贵州一次严重冰冻雨雪过程环境场分析

2008年1月10日至2月2日,我国南方发生了大范围的持续冰雪灾害,贵州是受灾最严重的省份之一。通过对高度场、温度、降水量、流场、涡度等要素场的分析,重点探讨此次极端气象事件对贵州影响最明显的第3次过程,以及形成严重冰冻雨雪天气和温度异常偏低的主要环流特征。结果表明,在强拉尼娜的背景下,稳定在乌拉尔山以东的阻塞高压持续存在、极涡异常偏强偏东、西太平洋副高偏西偏强、南支槽较常年活跃等,是造成这次过程的主要原因。主要特征是850 hPa以下出现温度低于0℃的冷空气层,在700 hPa附近是相对较暖的气层,其上层是较冷的冰晶层,西南低空急流及槽前正的相对涡度平流明显,急流带来的暖湿平流提供了充足的水汽,并保证了融化层中源源不断的热量供应,上下层涡度平流的差异有利于上升运动的发展,为贵州第3次雨雪过程的发生提供了条件。

Background Fields of Severe Ice/Snow and Freezing Disasters in Guizhou in Early 2008

Through analyzing the fields of height,temperature,precipitation,vorticity and other elements,the major features of the circulation pattern causing the freezing rainfall and abnormal low temperature weather,as well the process of the extreme snow and freezing event in January 2008 over Guizhou Province are discussed.The result shows that under the background of strong La Nina,the blocking high persisted in the east of the Ural Mountains,and the polar vortex was abnormally strong and farther eastern;the western Pacific subtropical high became stronger with active south branch trough,which were possibly the major causes of the disaster.The obvious features are that there existed a cold air layer of below 0 ℃ under 850 hPa,a warmer layer near the 700 hPa,and a colder ice layer above.There existed positive relative vorticity advection and a southwest low-level jet,which transported beneficial sufficient warmer and wetter air and sustained the steady flow of heat to the melting layer.The difference between upper and lower vorticity advection was favorable for the development of ascending motion,which provided conditions for the occurrence of the snow and freezing rainfall.