摘要
通过对2000年以来云南出现的4次强降雪过程进行分类对比分析和诊断分析,结果表明:横槽型和北脊南槽型是4次强降雪的主要中高纬环流形势,3次有南支槽配合,1次无南支槽活动,其中2次横槽型造成的强降雪范围广、强度大;4次强降雪过程云南西侧都有充沛的水汽输送,水汽通量增大(即水汽的增加)是云南强降雪的必备条件,强降雪出现在较强水汽通量辐合区中,且落区在辐合中心的偏东一侧、θse线陡立区附近以及暖湿不稳定区域;强降雪在多普勒雷达上显示为20-30 dBz左右的层状云回波,对流层中下层的高空冷暖平流和高空西南急流是有南支槽影响的强降雪天气的主要大尺度特征,而低层偏东急流是无南支槽影响的强降雪的主要特征,因此高低空急流的形成是强降雪的关键。
By using upper air observational data, surface observational data, MICAPS 1°×1°objective analysis data and Kunming Doppler Radar echo data, 4 heavy snow processes in Yunnan since 2000 are contrastively analyzed and diagnosed. The results show that in the 4 heavy snow processes in Yunnan, 2 processes aroused by the transversal trough pattern affect the western area of Ailao Mountain, the snow area is large with the strong intensity, the other 2 processes aroused by the north ridge and south trough pattern mainly affect the middle and the east Yunnan. 3 heavy snow processes accompany the southern trough. Warm and moist airflow in front of the south trough converges with the strong cold air, producing heavy snow. This is the major heavy snow pattern of Yunnan. But only one without south trough in 2005 is very special. Before and during the 4 heavy snow processes, the water vapour flux increases quickly. Most areas in Yunnan are in the big value band of the east-west water vapour flux, which indicates that plenty water vapour transports to Yunnan from the west whether the south trough exists or not. In 3 processes with active south trough, the water vapour comes from the southwest Bengal Bay and this is the main heavy snow pattern in Yunnan. In the heavy snow process without the south trough influencing, the water vapour comes to Yunnan from the west of Arabian sea along the India high pressure. The strong water vapour flux convergence belt and area can better indicate the heavy snow processes of Yunnan. The heavy snow always appears in the area of strong water vapour convergence and closes to the side of strong cold air in the east of the convergence center. Because the updraft and the downdraft in the south and the north coexist, the mesoscale vertical circulation near the front area may establish. When the cold air from the north moves to the south, the θse sharpness area also moves to the south, and then causes the water vapour brought by the south warm moist airflow to condense and the unstable energy to release, providing enough uplift condensation condition for the heavy snow. In the Doppler radar echo intensity field, the sheet cloud echo arouses the heavy snow, the intensity of sheet cloud echo is about 20 to 30 dBz. In the velocity field, the cold and warm adveetion＇s alternative change and the stronger southwest jet stream of the upper air in the middle and lower layer of troposphere are the major macro-scale characters of the heavy snow with the south trough in 2004. The partial east jet stream in the lower layer is the major macro-scale character of the heavy snow without the south trough in 2005. So the high and low level jet stream are the key to the heavy snow processes.
出处
《应用气象学报》
CSCD
北大核心
2007年第1期64-72,共9页
Journal of Applied Meteorological Science
基金
云南省"十五"攻关项目(2001NG43)资助。
关键词
强降雪
对比分析
诊断分析
多普勒雷达回波
heavy snow
contrast analysis
diagnosis analysis
Doppler radar echo
