北京西北部地区短时强降水环流特征分析
首发时间：2018-10-12
摘要：利用2009-2013年北京西北部延庆地区气象观测资料，分析短历时强降水物理量特征。结果表明，短历时强降水的影响系统主要可归纳为冷涡型、西风槽型和500 hPa西北气流型3类；降水多发生在12-18时和00-06时，以6、7月最多。3种类型温度场上500 hPa都是冷温槽，850 hPa处于或即将处于暖脊控制；850 hPa上都有较强的西南气流，不同的是冷涡型和西风槽型是冷涡或西风槽前的西南气流影响，而西北气流型是浅槽前偏西气流和高压脊外围偏南气流共同影响。3种类型降水发生前大气存在着较强的层结不稳定和对流不稳定，西北气流型最不稳定，冷涡型次之，西风槽型最小。低层水汽通量散度以西风槽型最大，冷涡型次之，西北气流型最小；冷涡型和西风槽型的水汽输送路径主要是西南低空急流携带的偏南水汽，而西北气流型则是西南低空急流携带的偏南水汽和副高外围的东南水汽输送。短历时强降水发生前北京西北部地区上空存在明显的水汽辐合，大气相对湿度、液态水含量和水汽总量都较大且有明显增加。短时强降水发生前北京西北部地区上空存在明显的水汽辐合，大气相对湿度、液态水含量和水汽总量都较大且有明显增加。3种类型在相对湿度达到或接近饱和的层次、液态水含量和水汽总量增长幅度方面有所不同，其中冷涡型最大，西风槽型次之，西北气流型最小。水汽辐合的强弱是3种天气型环流背景下是否发生短历时强降水的决定因素。
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Analysis of Circulation Characteristics of short-time heavy rain in northwestern Beijing
Abstract：By using observational data from Yanqing observation stations in northwestern Beijing during the period of 2009 to 2013, the short-time heavy rain (STHR) is analyzed. The results show that STHR major influence system is cold vortex、west wind trough and 500hPa north west air current. STHR occurs mainly in the afternoon (12h-18h）and after midnight（00h-06h）, that the most frequent between June and July. The Cold Trough on 500hPa temperature field, the warm high ridge on 850hPa temperature field, and 850hPa with strong south west air these features apply to all types. Except for the difference that the Influence of cold vortex and west wind trough is south west air current, the impact of north west air current are slot before by west airflow and outer ridge south airflow. There are strong stratification instability and convection instability in the atmosphere before STHR happen. Among the all types of STHR, north west air current is the most unstable, cold vortex the second and west wind trough the weakest. Meanwhile the moisture flux divergence has the same order from high to low. The water vapor transportation of cold vortex and west wind trough came from southwest low level jet carrying the south water vapor. North west air current have two water vapor paths, one is the same to the above path, another one is southeastern flow on the edge of the sub-tropical high. In addition to clear convergence of water vapor, there are a large value and increased significantly of the relative humidity, liquid water content and potential water vapor in the atmosphere over northwest Beijing before STHR happen. However, the level of relative humidity reach or close to saturation, liquid water content and total amount of water vapor growth are different in the three types, from high to low, it is cold vortex type, west wind groove type and northwest airflow type. The strong and weak of the low water vapor convergence in the background of three types are the determinants of whether occurred short-time heavy rain.
Keywords： northwestern Beijing short-time heavy rain instability water vapor convergence
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