一次低纬高原地区大到暴雪天气过程的诊断分析

利用常规气象观测资料、各物理量场、卫星云图和多普勒雷达资料等对2004年2月7日滇中及以东地区一次大到暴雪天气过程进行了综合分析。结果表明:新疆横槽转竖后东移,从北方来的冷空气不断向南扩散,在川滇黔间堆积加强,使昆明静止锋加强西移影响到云南中部;卫星云图的演变反映了南支槽云系有一个东移加强的过程,并与强静止锋云系交汇形成低纬高原上滇中及以东罕见的大到暴雪天气,由于地形的作用,滇西以小雨为主;高层西偏南风加强、水汽通量增大、上升运动的加强以及水汽的辐合造成滇中及以东的强降雪;同时强降雪过程中存在高空冷暖平流和高空急流,雷达图象也进一步证实了南支槽前的西偏南气流带来的水汽在低纬高原降雪中的重要性。

Diagnostic Analysis of a Heavy Snowstorm Processe in Lower Latitude Plateau of China

Using the conventional meteorological data,the various variable fields,the satellite and the Doppler radar echo images,the heavy snow process on February 7,2004 has been analyzed.The results show when the Xinjiang upper trough oriented in NE-SW direction changes its orientation into N-S direction and moves eastward,the cold air from the north diffuses continually southward,accumulates and intensifies in the boundaries among Sichuan,Guizhou and Yunnan,makes the Kunmin stationary front to intensify,move westward and affect the mid-Yunnan province.Meanwhile the satellite images also show that the cloud area of the southern brauch trough in India intensies,moves eastward and merges with the forementioned strong stationary front cloud area,so the moderat-heavy snow storm occur in mid- and east-Yunnan.Because of the function of the relief,there is light rain in west Yunnan mostly.Southwest wind enhancement,water vapour flux increase,ascending motion enhancement and water vapour convergence in upper level arouse the heavy snow process in central and east Yunnan.In the meantime the cold and warm advections and the southwest jet in upper level are the main characters of the heavy snow in the Doppler radar velocity fields.This further substantiates that the water vapor condition brought by southwest airflow is very important to snowfall in lower latitude plateau.