干侵入对陕西“2008.07.21”暴雨过程的影响分析  

Analysis of Influence of Dry Intrusion on Rainstorm on 21 July 2008 in Shaanxi Province

作　　者：白涛[1,2] 李崇银[1,3] 王铁[1] 谭言科[1] 李刚[1] 

机构地区：[1]中国人民解放军理工大学气象海洋学院 [2]中国人民解放军94162部队 [3]中国科学院大气物理研究所LASG实验室

出　　处：《高原气象》2013年第2期345-356,共12页Plateau Meteorology

基　　金：国家自然科学基金项目(U833602)资助

摘　　要：利用NCEP/NCAR再分析资料,分析了2008年7月21日发生在陕西西南部一次暴雨过程的大尺度环流背景和水汽条件,运用相对湿度、风矢量、湿位涡和垂直涡度等多种物理量场,研究了该暴雨过程中干侵入的机制和特征,以及对暴雨发生、发展和维持的影响。结果表明,此次强降水过程是在高空槽和低空气旋的有利形势下产生的。水汽主要来源于孟加拉湾,持续的高层辐散、低层辐合的环流配置保证了低层源源不断的水汽辐合并抬升凝结,有利于转化为降水。受高空低槽发展东移的影响,干侵入在垂直层次上表现为由对流层中高层向低层的注入,水平方向上主要表现为由西向东的侵入,其中在103°E以西地区存在较强的下沉运动是干侵入的载体。应用湿位涡与倾斜涡度发展理论分析表明,当对流层中高层具有高值位涡的干空气侵入到低层时,由于湿位涡守恒特性,引起倾斜涡度发展,进而导致低层垂直涡度的急剧发展,有利于上升运动将水汽向上层输送,冷暖空气相遇,产生此次暴雨过程。Based on the NCEP/NCAR reanalysis datasets, the large-scale circulation and water vapor conditions of the rainstorm process on 21 July 2008 occurred in southwest of Shaanxi have been analyzed. By employing multiple variations （such as relative humidity, vector wind, moisture potential vorticity, and vertical vorticity）, the characteristics and mechanisms of the dry intrusion, as well as its impacts on the formation, development and maintenance of the rainstorm are explored. It is founded that the development of the upper-level trough and low-level cyclone are helpful to the occurrence of rainstorm event. The water vapor mainly comes from the Bay of Bengal, The circulation configuration of sustained high-level divergence and low-level convergence is in favor of plenty of low-level water vapor convergence, ascent and con- densation motion, which can provide an advantageous condition for the conversion of precipitation. Influ- enced on moving eastward and development of the upper-level trough, dry intrusion can be mainly observed in two patterns, in the vertical direction, the dry air from the mid-upper troposphere can be extended into the lower troposphere; in the horizontal direction, the dry air can intrude from west to east. The stronger descending motion exists to the west of 103°E , which could be recognized as the carrier of the dry intrusion. The analysis of moisture potential vortieity and slantwise vorticity theory shows that, when the dry air along with high potential vorticity from mid-upper troposphere intrude into lower troposphere, the slantwise vorticity and low-level vertical vorticity develops due to the conservation of moisture potential vorticity, which facilitates ascend motion brings water vapor upward. When cold air and warm air interacts, the rainstorm event happens.

关 键 词：干侵入 暴雨 湿位涡 倾斜涡度 

分 类 号：P426.62[天文地球—大气科学及气象学]