【摘要】 利用ECMWF和Micaps提供的常规观测资料,对2008年1月华南西部遭遇50年罕见的低温雨雪冰冻极端天气事件过程进行分析。结果表明:蒙古横槽南压分裂小槽东移,使地面冷高压强度突然增强并爆发南下,是造成华南西部寒潮天气的起因;北半球中高纬度出现双阻型高压(乌拉尔山阻高和阿留申群岛阻高),使大气环流形势异常稳定,是导致低温雨雪冰冻天气持续性的直接原因;低纬度南支低压槽活跃,西南暖湿空气不断向我国南方输送,华南西部低空相对湿度大,水汽辐合条件及上升运动都对阴雨天气的维持有利;在850hPa华南上空形成一支稳定的强锋区,大气层出现近地面冷、中层暖、高层冷的结构,加剧了雨雪冻雨的形成。更多还原

【Abstract】 By using the ECMWF data and the conventional observations from MICAPS,an extreme weather event of chilling temperature, icy rain and freezing in January 2008, which has rarely been witnessed for the past 50 years in the west of South China, is analyzed. Results show that the cold air wave in the west of South China was caused by a Mongolian transversal trough moving southwards and braking up into some smaller troughs, which then moved eastwards and led to the strengthening, breaking out and moving southwards of a surface cold high pressure. The direct cause of the persisting chilling temperature, icy rain and freezing weather was two middle- and high- latitude blocking highs over the Ural and the Aleutian in the Northern Hemisphere, which made the air circulation extraordinarily steady. An active southern trough over low latitudes continuously transported the southwest warm and moist flow to South China and formed a steady and strong frontal zone at 850 hPa. At lower levels, both high relative humidity and favorable water vapor convergence and ascending motion are all beneficial to the maintenance of excessive rain in South China. And the atmospheric structure of being cold at both surface and upper levels but being warm at the middle level intensified the formation of the icy rain.更多还原