我国南方低温雨雪冰冻灾害期间阻塞高压异常特征分析

Abnormal Characteristics of Blocking High during Durative Low Temperature,Snowfall and Freezing Weather in Southern China

利用NCEP/NCAR 2.5°×2.5°再分析资料和PV-θ阻高指数,分析了2008年初我国南方发生的低温雨雪冰冻灾害。结果表明,欧亚大陆3个关键区的阻塞高压(简称阻高)在此次灾害发生的环流背景中起着非常重要的作用,并存在异常特征。与1950—2008年历史同期相比,2008年初乌拉尔山和贝加尔湖阻高发生的日数显著偏多,而鄂霍茨克海地区无阻高发生;乌拉尔山阻高的强度偏强,而贝加尔湖阻高的强度则偏弱;乌拉尔山地区最大PV-θ阻高指数发生的位置比大多数年份偏东,而贝加尔湖地区最大PV-θ阻高指数发生的位置比大多数年份偏西,这种位置的异常特征说明此次我国南方低温雨雪冰冻灾害期间欧亚大陆关键区阻高在位置上很集中。3个关键区的阻高在发生日数、强度以及位置上异常特征的共同配置,使得分裂出的小槽活动偏多,造成冷空气活动频繁并不断南下补给,加之此时的异常环流特征,共同造成这次低温雨雪冰冻灾害。

During the early 2008,southern China was hit by durative low temperature,snowfall and freezing weather disaster,which was a rare weather extreme in history because of its wide influencing area,high strength and long durative time.Blocking high in three key regions of the Eurasia played very important role in the general circulation of this disaster,with three abnormal characters： Comparing with character of blocking high during the same period from 1950 to 2008,in early 2008,the blocking days were more in Ural Mountain and Lake Baikal,while no blockings occurred in Okhotsk Sea;blocking high was stronger in Ural Mountain and weaker in Lake Baikal and Okhotsk Sea;the biggest PV-θ blocking index was east of that in the most blocking years in Ural Mountain,but west of that in the most blocking years in Lake Baikal which indicated that blocking high were concentrated in the Ural Mountain and western Lake Baikal during this extreme weather disaster.Abnormal characteristics of blocking days,strength and blocking location,brought more action of small trough and cold air supplied to the cold waves by long time persistence.Accompanying with other abnormal factors of general circulation,it eventually caused such durative low temperature,snowfall and freezing weather disaster.