四川盆地两次冬季寒潮天气过程对比分析

本文利用欧洲中期天气预报中心ERA-Interim全球再分析资料，常规地面、高空观测资料，及地面自动站观测资料，对2018年12月5～7日和27～29日四川盆地两次典型寒潮天气过程进行了对比分析。结果表明:两次过程均是在前期升温的基础上，500hPa欧亚中高纬度为一脊一槽，地面有强冷空气在中西伯利亚堆积，横槽转竖引导冷空气爆发南下造成的；冷空气爆发后，由于寒潮发生的环流背景、影响系统和冷平流强度、发展、路径不同，由此带来的天气现象和对四川盆地的影响也不同。两次过程中南支槽强度、移动速度和持续影响四川盆地时间存在明显不同，但当南支槽东移至85°E及以东位置时，南支槽显著加深，槽前强西南气流将暖湿水汽输送到四川盆地，并与南下的偏北冷气流交汇，导致四川盆地的降雨明显加强，降温幅度也加强。气温骤降，当盆地850hPa温度低于-5℃，1000hPa温度低于4℃，0℃层降到940hPa以下高度时，降水出现雨向雨夹雪或雪转换。 

Comparative Analysis of Two Cold Wave Events in the Sichuan Basin in Winter

Using the ERA-interim reanalysis data and observation data,this study investigate the synoptic characteristics of the two cold wave events,with a focus on the conditions for formation of large snowfall.The results showed that the two cold wave events occurred after the days with higher-than-normal temperature,and are accompanied by a strong trough and ridge at the middle and high latitudes in Eurasian at 500hPa,cold air accumulated in the middle Siberia,while these features are clearly different between the two cold wave events.There is a strong trough located to the south of the Tibetan Plateau for the two cold wave events,with different strength,speed and life time.The two events share some common features:the strong southwesterlies at the eastern part of the trough to the south of the Tibetan Plateau transport large amount of tropical warm and moist air to the Sichuan Basin when it moves eastward to the 85° E,causing precipitation by converging with the cold and dry air outbreak from Siberia.Temperature in the Sichuan Basin drops quickly after rainfall.Due to the quick decrease in temperature,rainfall shifts to snowfall when the air temperature at 850hPa, 1000hPa and 940hPa levels is lower than-5℃, 4℃and 0℃.