2008年湖南极端冰冻特大灾害天气成因分析

Analysis on Extreme Freeze Catastrophic Weather of Hunan in 2008

2008年初,湖南出现了有完整气象记录以来罕见的特大低温冰冻雨雪极端灾害天气。常规资料分析表明,高空中高纬阻塞高压稳定,副高持续偏强,孟加拉湾低槽稳定少动,湖南一直处于槽前西南气温中;700hPa西南急流带来大量暖湿气流,一方面有利于降水的形成与持续,另一方面有利于逆温层的形成;850hPa切变线在湖南境内南北摆动,造成全省大范围降水;地面冷空气不断从洞庭湖区补充南下。大环流背景有利于低温冰冻天气的维持。分析探空站的大气层结、地面气象要素与冰冻的关系表明:大气层结的逆温层、融化层,地面温度在0℃附近及以下是形成冰冻的关键因子;降水对于冰冻的形成具有重要作用,日降水量大于0.1mm持续性大范围稳定性的雨夹雪或小雨有利于冰冻的形成与加强;气温与冰冻的发展呈反相关;当大气层结、降水量与海拔高度基本相同时,气温是冰冻发展的关键因子。

At the beginning of 2008, Hunan province experienced an extreme freeze catastrophe that is rare since the complete meteorological record has been set. Analysis with conventional data indicates that the stable block high in the middle latitude at high level of atmosphere, sustained strong subtropical high pressure, and stable Bengal trough kept Hunan in the southwest stream of the leading area of trough. Warm and wet air mass brought by southwest jet at 700hPa sustained the persistent precipitation and it was favorable for the temperature inversion. The shear line at 850hPa oscillated within Hunan, the surface cold air invaded southw-ards from Lake Dongting and led to large area precipitation. The macroscale circulation provided favorite background for the freeze disaster. Research on the relation among the air vertical structure, surface meteorological elements and freeze shows that the layers of inversion, melting layer and the surface temperature below 0℃ are key factors to form the freeze, the liquid precipitation played an important role, and the daily rainfall above 0. 1mm was favorable for the formation and development of freeze. The property of precipitation is an important factor. The persistent, large scale and stable drizzle and sleet are beneficial to the formation and development of freeze. Air temperature shows negative correlation with freeze development. The temperature is the crucial for freeze when the vertical structure, precipitation and geographic height are similar.