2008年1月我国南方持续雨雪过程的诊断分析

Diagnostic Analysis on Severe Cold Surge,Rain and Ice-Snow in South China in January 2008

采用T213L31产品模式大气资料,对2008年1月我国南方雨雪过程的天气尺度的凝结函数降水、水汽通量辐合降水,以及对流不稳定与层结湿不稳定降水做诊断计算。结果表明,大尺度稳定性上升运动的凝结函数降水场和天气尺度波动的水汽通量辐合降水场,可以反映西风带天气系统,进而反映长波调整与更替及伴随"槽来脊去"的大尺度水汽场相变变化,以及它们组织中尺度对流不稳定降水过程。La Ni^na事件是2008年1月欧亚大陆大气环流异常的物理背景,在西风带"上(下)游效应"和全球遥相关大气波动影响下,东亚冬季经圈环流和冬季风得到增强,同时,西太平洋副热带高压偏强、偏北,其西侧北上暖湿低空急流与南下的冷空气相遇,造成这次我国南方持续异常的雨雪冰冻天气过程。因受地面冷锋和高空槽活动的影响,凝结函数降水和水汽通量辐合降水是这一次多次雨雪、乃至大到暴雪降水过程的主要原因,而对流不稳定降水和层结湿不稳定降水只在初冬那次强冷空气雨雪过程中贡献大,且仅出现在江南和华南地区。

Using the atmosphere data of T213L31 model,four forms of synoptic precipitation with perpendicular motion,i.e.condensation-function precipitation,moisture-flux divergence precipitation,convective unstability precipitation and stratificative unstability precipitation are designed and diagnostic calculated for analyzing the severe cold surge,rain and ice-snow in South China during January 2008.The large-scale,stable ascending motion of the condensation-function precipitation and the synoptic-scale wave of the moisture-flux divergence precipitation can both reflect synoptic systems,as well as their real precipitation,in the atmospheric westerly belt,and response of the long wave adjustment and reset processes,accompanying so called ＇coming trough and going ridge＇ with large-scale moisture phase change in the air saturation field,and both could organize the mesoscale stratificative unstability precipitation motions.Because the La Nia event is the background for the unusual general circulation over the Eurasian continent during January 2008,the winter meridional circulation and East Asian monsoon should be improved,against that of the ocean-atmosphere interplay,the up/down stream effect in waves of the westerly belt and the teleconnection in the atmosphere,meanwhile,the subtropical high may be stronger and northward then normal in the West Pacific,therefore the severe cold surges,coming from the Siberian High and the Mongolia High,invade southwardly to China and meet with worm and wet jet-flows northwardly in the lower troposphere,which come from west side of the subtropical ridge and maintain long time,so that,the anomalous weather of rain,freezing rain and ice-snow take place in South China.It shows that,in view of the diagnostic calculations of synoptic precipitation motions for the activities of such surface cold front,upper trough and low eddy,etc.,the condensation-function precipitation and the moisture-flux divergence precipitation were two main weather forms in 4 times of rain and/or snow in the winter 2008,while the convective unstability precipitation and the stratificative unstability precipitation just occurred at the first time of heavy rain and snow in South China,that accompanied by a long wave adjustment and a severe cold surge.