一次华南暴雨的中尺度结构及复杂地形的影响

THE MESOSCALE STRUCTURE OF A SOUTH CHINA RAINSTORM AND THE INFLUENCE OF COMPLEX TOPOGRAPHY

中文关键词:  华南  暴雨  中尺度  地形

英文关键词:South China  Rainstorm  Mesoscale  Topography

中文摘要:

      文中选取了1998年6月8～9日的一次发生在华南的强降雨过程,利用观测资料和MM5中尺度模式对这个过程进行了诊断分析和数值模拟,研究了该暴雨过程的中尺度结构及华南地区复杂地形的影响。分析表明这次华南暴雨由锋面暴雨和暖区暴雨组成,具有不同的中尺度结构,其中广西梧州地区暴雨是准静止锋面上的中尺度对流系统造成,具有持续时间短,强度大的特征,MM5模拟的雷达回波强度超过30dBz,高度超过200hPa,并在其东、北侧出现闭合的次级垂直环流;珠江三角洲的暴雨是暖区暴雨,发生在深厚的暖湿气流内,850hPa上强度超过16m/s的西南低空急流是影响降水的主要系统,该中心暴雨持续时间较长,降水强度也达到了暴雨标准,模拟雷达回波不明显,没有出现局地的次级环流。华南地区的复杂地形在这次华南暴雨过程中主要为动力性作用,具体表现在一支冷空气在低层由苗岭和南岭之间南下,南海上空一支暖湿气流北上直接到达梧州地区,另一支次暖湿空气在南岭的阻挡下由武夷山以南沿南岭和云开大山之间折而向西,这三支气流在梧州地区附近汇合,形成广西梧州地区的暴雨;同时南海上空北上的低层气流被迫向东北绕行海南岛,形成一个尺度为200km左右的背风面气旋,这个气旋的东北部分加强了在珠江三角洲地区的水汽辐合,导致降雨加大。

英文摘要:

      A rainstorm happening in South China during 8-9 June 1998 is selected in this paper. Diagnoses and numeric simulation are made on this rainstorm using observed data and MM5 model, to get the mesoscale structure of the rainstorm and the influence of complex topography. The results show that the rainstorm is made up by a frontal precipitation and a warm sector precipitation that have different mesoscale structures. The rainstorm happening at Wuzhou district in Guangxi Region is inspired by an MCS on a quasi-stationary front, which maintains a long time and has large intensity. The rainstorm happening at the Delta of Zhujiang River is a warm sector precipitaton, which also lasts for a long time and also has large intensity. The influence of the complex topography is dynamic. In the Wuzhou rainstorm, three branches of air current that are all affected by the topography converge at the center of the rainstorm. In the Zhujiang rainstorm, the warm air current is forced to move around the Hainan Island and strengthened the convergence over the Delta of Zhujiang River.