清远一次极端龙舟水的中尺度系统演变分析

Analysis of the Evolution of Mesoscale System for an Extreme Dragon⁃boat Rain in Qingquan

利用多源观测数据和ERA5再分析资料,对2022年6月20到21日发生在清远的一次极端特大暴雨过程进行分析。结果表明:(1)该次强降水是在200 hPa分流辐散的背景下,由低涡切变配合其前侧西南急流缓慢东移经过清远造成的。(2)强降水发生前大气层结已处于极不稳定状态,低层来自孟加拉湾和南海的水汽不断在清远市上空辐合,为暴雨的发生提供充足的水汽条件和不稳定能量。(3)强降水的触发机制主要是前期广西降水造成的冷池与低空急流带来的暖湿气团形成的温度锋区和地面辐合线;地形的抬升作用和狭管效应,对降水起到增幅作用。(4)该次强降水主要有2个低质心的热带海洋型中尺度对流系统先后影响发生。

Using data from multiple sources and the ERA5 reanalysis,this paper analyzed the process of an extreme and exceptionally heavy rain that took place from June 20 to 21,2022 in Qingyuan.The re⁃sults are shown as follows.(1)Under the background of diverging flows at 200 hPa,the intense rain of in⁃terest formed as a low⁃vortex shear was in the company of a southwesterly jet stream at its front moving gradu⁃ally across Qingyuan during its eastward travel.(2)Prior to the intense rain,the atmospheric stratification was already highly unstable so that water vapor from the Bay of Bengal and South China Sea kept converging over the city,supplying sufficient amount of water vapor and instability energy for the occurrence of the heavy rain.(3)The intense rain was mainly triggered by a temperature frontal zone and a surface conver⁃gence line,which resulted from a warm and humid air mass brought about by a cool pool and a low⁃level jet stream due to earlier rain in Guangxi.The rain was enhanced owing to topographic lifting and funneling effect.(4)The intense rain took place as it was affected successively by two mesoscale convective systems,which was of tropical marine type and with low mass cores.