摘要
采用NCEP逐日4次1°×1°再分析资料和Micaps常规观测等资料,对2011年4月发生在中天山北坡乌鲁木齐地区寒潮型暴雪过程的致灾天气学成因进行综合分析,着重讨论了强降雪发生所具备的水汽条件、高低空急流等动力耦合机制及温度平流条件。结果表明:在稳定的环流背景下,春季500 h Pa西西伯利亚低槽位置南伸至35°N,使得冷暖空气活跃交绥造成中低层大气斜压性增强,加之天山准静止锋的长时间停滞维持,致使中天山北坡受强锋区的控制而形成持续性雨雪天气。深厚的湿层和持续的水汽辐合为暴雪的产生提供了丰沛的水汽条件;高低空急流配置及正涡度大值区由低层向对流层中层发展,有利于高层气流抽吸辐散、中低层暖湿气流辐合和上升运动的增强,为强降雪天气提供了动力条件;强降雪落区与湿位涡有较好的对应关系。冷暖平流稳定对峙加之低层冷平流侵入之强是造成暴雪持续、增幅和剧烈降温的重要原因之一。
Based on the conventionally observational data and NCEP 1o×1o 6-hour interval reanalysis data,one snowstorm event occurred at Urumqi in the middle Tianshan Mountain,Xinjiang,China on April 2011 is comprehensively analyzed. The water vapor,upper-lower jet conditions and temperature conditions are diagnosed. The results indicate that under the stable circulation background,the enhanced 500 h Pa West-Siberia trough was extended to 35°N that makes activity cold and warm air together in the low level. The atmospheric baroclinicity enhanced the Quasi-stationary front in the Tianshan maintained for a long time,resulting in the two branch frontal zones converged north-southward with a strong front control and continuing snowy weather in the north slope of Middle Tianshan Mountain. The deep moisture layer and the sustained water vapor convergence together provided plentiful water for the snowstorm;the configuration of high and low jet and development of positive vortex from lower layer to the middle of troposphere were beneficial to upper-level divergence,lower-level warm-wet air convergence and persistent increase in vertical ascending motion,which provide dynamic condition for the snowstorm. The strong storm area corresponded well to the moist potential vorticity. It is showed that the stable confrontation condition of warm and cold advection and wedging of cold air are one of the important reasons that causes snowstorm continuing and increasing,while the low-level cold air advection plays the key role for maintaining lower air temperature during the whole snowfall period. As the height of the 0 ℃-level bright zone atmospheric layer is lower than that of the 950 h Pa,the character of precipitation will change from rain to snow. Furthermore,the diagnosis showed that it is the surface air temperature decreases to near freezing point rapidly that let the precipitation transit from rain to snow.
出处
《干旱区地理》
CSCD
北大核心
2015年第3期478-486,共9页
Arid Land Geography
基金
中国沙漠气象科学研究基金(SQJ2009003)
新疆维吾尔自治区科技计划项目(2013911016)
关键词
寒潮
暴雪
水汽通量
温度平流
致灾成因
cold wave
snowstorm
water vapory flux
temperature advection
disaster-caused
