1.中山大学大气科学学院，珠海 519082;2.南方海洋科学与工程广东省实验室(珠海)，珠海 519082;3.国家气象中心，北京 100081;4.成都信息工程大学大气科学学院，成都 610225
1.School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai 519082;2.Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082;3.National Meteorological Center, Beijing 100081;4.School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225
National Key Research and Development Program of China Grant 2017YFC1502501National Key Research and Development Program of China (Grant 2017YFC1502501)
在华南北部或长江流域有锋面雨带活动时，华南沿海常常会出现对流性强降水，突发性很强，给预报造成很大的困惑。文章采用多种观测资料、ERA-Interim 0.125°×0.125°逐6 h再分析资料，对2017年6月15～16日华南北部的锋面雨带及沿海强降雨过程开展分析，对比了二者降水特征与环境条件，重点探讨了该次过程华南沿海强降雨的对流触发与维持，揭示了一种由边界层风切变强迫造成涡度持续发展的动力效应。结果表明：（1）锋面雨带与华南沿海强降雨在降水特征上有显著差异，并各有特点。锋面雨带以大尺度层状云降水和弱对流性降水为主，降水强度东段弱西段强。沿海强降雨以对流性降水为主，局地性强、落区集中、强降雨持续时间长、夜发性明显。（2）水汽方程诊断发现沿海强降雨在边界层水平水汽平流项、垂直水汽输送项比锋面雨带东段具有更大量级，大气层结反映出更深厚的暖层、湿层与对流不稳定，是二者降水强度及性质差异的主要原因。（3）莲花山、峨眉嶂造成气流侧向摩擦与正面阻挡促使漯河河谷内垂直涡度发展，暖湿空气堆积上升并达到自由对流高度，触发了华南沿海最初的降水。夜间建立的西南风急流使边界层垂直风速切变增强，水平涡度倾斜部分转化为垂直涡度发展，与风速水平切变造成的垂直涡度叠加，是强降雨持续时间长的动力机制。海陆边界摩擦差异造成水平、垂直两个方向的风切变增强，共同强迫垂直涡度发展是此次强降雨过程对流维持的动力效应。（4）
Torrential rainfall often occurs at the coast of South China, with background of frontal rain band over northern South China or the Yangtze River basin, but it is difficult to forecast. Based on multiple observation data and ERA-Interim 0.125°×0.125° interval 6 h reanalysis data, we researched coastal torrential rainfall event from 15 June to 16 June 2017. We contrasted the precipitation characteristics and ambient atmospheric conditions between frontal rain band and coastal rainfall, and analyzed convection initiation and maintenance mechanisms for the latter. Finally, dynamic effect of the convection maintenance was proposed. The results are as follows. (1) There was considerable discrepancy between frontal rainfall and coastal rainfall. The former is presented as stratification cloud rainfall and weak convective rainfall caused by synoptic scale system (cold front), and its intensity is heavier to the west than that to the east. The latter characterized with convective, local, concentrated, and long-lived, which occurred at midnight. (2) Horizontal water vapor advection and vertical water vapor transport within boundary layer accounted for discrepancy between frontal rainfall and coastal rainfall. Owing to convective instability in middle and low troposphere associated with warm and moisture transport, rain rate over coastal South China is notably higher than those under the east of frontal rain band. (3) Lateral friction and direct block from the Lianhua Mountains and the Emei Hills caused vertical vorticity develop in river valley Luohe, ultimately triggering updrafts and convection initiation. Horizontal vorticity developed with strengthening of vertical wind shear, while southwesterly jet in boundary layer enhanced at midnight, and horizontal vorticity then partly converted into vertical vorticity, overlying the vertical vorticity originated from lateral friction and direct block. The process above is responsible for the long duration of coastal rainfall as well as dynamic effect of convection maintenance. (4) Rainfall sustaining long duration is also associated with the coutinuous releasing of convection latent heat. Upward vertical velocity caused by thermal buoyancy related to convection latent heat accounted for 39%-75% of total updraft vertical velocity.