2008年1月我国南方严重冰雪灾害过程分析

Severe Snow and Freezing-Rain in January 2008 in the Southern China

2008年1月中旬至2月初,我国南方地区出现大范围持续性雨雪天气过程。江淮流域降水出现类似某些夏季强梅雨期的降水过程,而且,江南的冻雨在历史上属少见。这次大范围冰雪天气过程的成因是由于欧亚大陆出现异常的大气环流。1月中下旬亚洲中高纬60～100°E地区的阻塞形势稳定维持20余天,里海以东地区长期维持一个切断低压系统,在这个切断低压下游地区有3次低气压扰动沿青藏高原向东移入我国上空;这时欧亚大陆20～35°N地区南支高空西风急流异常偏强,来自大西洋的大气扰动沿这条急流波导向下游地区传播,欧亚地区Rossby波列的下游发展效应显著。从1月16日开始到2月初,在20～40°N范围内,30°W、15°E和85°E（青藏高原附近）地区持续有高空槽发展,而在5°W、50°E和135°E（日本南部）稳定有高空脊维持。我国南方地区处于80°E的“南支槽”前,大量暖湿空气被输送到我国南方。此外,1月中下旬原来位于15°N的西太平洋副热带高压移到20°N,副高西北侧的西南气流有利于将来自南海的暖湿空气输送到中国南部大陆。在这样稳定的异常环流形势下,当一次次从高原西侧过来的高空高位涡扰动移到位于华南上空的静止锋上时,诱发低层静止锋锋生引起一次次降水过程。另一方面,由于大量暖湿空气沿着锋面抬升,在江南南部和华南北部形成了持久的温度高于0℃的逆温层（暖盖）,使得在这些地区出现严重的持续性冻雨天气。

The severe snow and freezing-rain in January 2008 affected the Southern China.The heavy snow storm mainly occurred in the Yangtze and Huaihe River Valleys,and the freezing-rain affected from Guizhou,Hunan,Jiangxi to Zhejiang Provinces.The damage that the storm caused was very serious,with the economic losses of about 151.65 billion Yuan,and particularly the damage of power delivery infrastructure in the Southern China.The atmospheric processes associated with the storm are analyzed.During the storm period,a large blocking circulation system stayed over the Asian continent with a blocking high pressure to the north of the Lake Baikal and a cut-off low near the Caspian Sea.There was a strong jet stream in the upper troposphere extending from the Mediterranean Sea,Tibetan Plateau,South China to the southern part of Japan.The blocking circulation system lasted for 22 days.During the storm period there was a quasi-stationary front in the Southern China with a frontal zone extending from the coast of South China in the lower troposphere to the Yangtze and Huaihe River Valley in the middle troposphere.At that time,cold air was shifted southward at low levels leading to a cold air damming.At mid-levels（850-200 hPa）,a southerly flow advected warm and moist air from the South China Sea,forming a melting layer（t〉0 ℃） in the Southern China which is a necessary condition for the formation of freezing-rain.There was a long-lived developing Rossby wave packet along the jet stream over the Southern Asia leading to the formation of a trough（at 85°E） and ridge（at 135°E） pair over the Southern China,enhancing the advection of warm and moist air in the Southern China.These meteorological conditions are commonly associated with winter snow and ice storms in the Southern China.During the storm period there were regions of cyclonic potential vorticity which advected from the cut-off low near the Caspian Sea along the jet stream over the Tibetan Plateau downstream to the quasi-stationary front in the Southern China on 16-22 January,25-29 January and 30 January-2 February 2008,respectively.The advection of cyclonic potential vorticity to the frontal zone is a favorable condition for the frontgenesis of the stationary front in the Southern China,leading to heavy snow and severe freezing-rain in January 2008 in Southern China.