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地形与城市环流共同作用下的β中尺度暴雨
引用本文:孙继松,杨波.地形与城市环流共同作用下的β中尺度暴雨[J].大气科学,2008,32(6):1352-1364.
作者姓名:孙继松  杨波
作者单位:1.北京区域中心气象台, 北京 100089;中国气象局北京城市气象研究所, 北京 100089
基金项目:国家自然科学基金资助项目40505002, 北京市自然科学基金项目8051002, 国家公益性行业 (气象) 科研专项项目 (GYHY200706004) “京津冀城市群强对流天气短时临近预警关键技术研究”
摘    要:从中尺度天气动力学理论入手, 利用尺度分析的方法, 得到了地形与城市热岛共同作用下的β中尺度暴雨的一系列理论特征。利用北京地区稠密的地面观测网资料以及分布于距暴雨中心区不同距离的两部风廓线仪观测资料, 通过分析2006年夏季发生的3次β中尺度暴雨酝酿、 发生、 发展、 维持过程中的气温、 降水、 风场的配置关系, 对β中尺度暴雨的部分理论特征进行了验证。主要结论: (1) 由城市热岛形成的水平温度梯度有可能在靠近城区的山前迎风坡强迫产生相对独立的中尺度风的垂直切变, 由此产生的低空风的垂直切变是维系中尺度对流降水发生、 发展的重要条件。另一方面, 一旦迎风坡出现强降水, 将形成吹向迎风坡的风速与降水强度之间的正反馈现象, 这种正反馈过程对β中尺度暴雨的形成过程起到了重要作用; (2) 地形越靠近城区, 山前越容易形成强的水平温度梯度, 进而越容易出现低空风的垂直切变。形成强低空风的垂直切变的响应时间取决于水平温度梯度的强度; (3) 地形坡度越大的地方, 产生的上升运动越强, 中尺度系统的水平尺度越小, 对于地形坡度较为平坦的地方, 更有利于产生水平尺度较大的中尺度系统; (4) 一般情况下, 地形与城市热力过程造成的中尺度暴雨过程多发生于傍晚前后或凌晨前后。

关 键 词:β中尺度暴雨  地形  城市热岛  垂直切变

Meso-β Scale Torrential Rain Affected by Topography and the Urban Circulation
Sun Jisong and Yang Bo.Meso-β Scale Torrential Rain Affected by Topography and the Urban Circulation[J].Chinese Journal of Atmospheric Sciences,2008,32(6):1352-1364.
Authors:Sun Jisong and Yang Bo
Institution:1.Beijing Regional Meteorological Center, Beijing 100089;Beijing Urban Meteorological Institute, China Meteorological Administration, Beijing 1000892.Beijing Regional Meteorological Center, Beijing 100089
Abstract:Some theoretical features of meso-β scale torrential rain, which are caused by joint action of topography and the urban heat island, are gained by mesoscale dynamic meteorology theory and scale analysis. Using observation datasets with high spatial-temporal resolution based on auto-weather station network and wind profile data from two profilers which are located at different positions, most of the theoretical features are confirmed by three cases which occurred in Beijing in the summer of 2006. The results indicate that (1) the temperature gradient in front of mountains, mainly caused by the urban heat island, is able to engender a relatively isolated vertical wind shear near the windward slope, and the shear is much more important to grow, develop and maintain the mesoscale convective system. The closer the mountain is to urban areas, the stronger the temperature gradient in front of mountains is, and the local stronger vertical wind shear is easy to be at the position. On the other hand, the response time of strong vertical wind shear depends on the intensity of temperature gradient. (2) Once stronger convective precipitation begins on the windward slope, the positive feedback between rainfall intensity and horizontal wind velocity toward the windward slope will appear, and the process is an essential condition to form meso-β scale torrential rain. (3) The stronger the terrain grade is, the stronger ascending motion will be forced and the smaller horizontal-scale mesoscale weather system will be stirred; in front of smoother topography, however, the mesoscale system at a relatively larger horizontal scale is easy to be formed. (4) generally, most of the mesoscale torrential rain processes, which are caused by joint influence of topography and thermodynamic urban circulation, should occur in front of mountains in the evening or the early morning.
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