2002年8月云南低温冷害天气的气候特征及其成因分析

The climatic characteristics and its causes ofYunnan chilling damage in August 2002

2002年8月云南省的滇中及以北以东地区出现了一次范围大、持续时间长、危害较为严重的低温冷害天气,初步分析发现,这是1974年以来全省8月降温幅度最大,范围最广的一次低温冷害天气,它是发生在一个暖背景下的一次异常事件;其前期1～7月北半球100hPa和500hPa高度场均更相似于云南8月典型高温年的高度场,为预测增加了难度.在这次低温冷害天气期间,中高层(200hPa,500hPa)的中高纬度为明显的经向环流,云南位于槽后脊前,为明显的偏北气流控制;在低层(700hPa)云南省为偏南气流控制,中高层与低层形成明显的风切变,这种配置为低温阴雨天气提供有利的动力和水汽条件.同时北方冷空气的维持和不断的补充是2002年8月低温冷害发生的一个重要条件.

A severe chilling damage that was the widest range and the largest temperature decreasing rate since 1974 took place in the middle,north and east area of Yunnan.It belongs to abnormal event in warm climatic background.From January to July,northern Hemisphere 100?hPa and 500?hPa height fields warm were more similar those of leading to high temperature of Yunnan in August.As a result,the chilling damage in August was very difficultly predicted.During the chilling damage,the high and middle latitude on 100?hPa and 500?hPa were dominated by meridional circulation.Yunnan province located behind trough and before riddle and was controlled by northward wind.On 700?hPa,Yunnan province was controlled by southward wind.So there was obviously vertical wind shear between the upper-level and the low-level,which provided dynamic and moisture condition for the chilling damage.At the same time,the maintenance and continuous complement of northern cold air were important conditions which cause the chilling damage in August 2002 take place.