粤港澳大湾区一次局地极端强降水过程的多尺度观测特征与演变分析

MULTI-SCALE OBSERVATIONAL CHARACTERISTICS AND EVOLUTION OF THE 22 MAY 2020 EXTREME RAINFALL IN THE GUANGDONG-HONG KONG-MACAO GREATER BAY AREA

关键词:  极端降水  降水特征  暖区暴雨  中尺度特征  中尺度对流系统

Key words:  extreme rainfall  precipitation characteristics  warm-sector heavy rainfall  mesoscale characteristics  mesoscale convective system

摘要:

2020年5月22日凌晨粤港澳大湾区发生了一次极端强降水过程，最大小时雨量和3小时雨量打破广东省内“龙舟水”期间的历史最高纪录。利用多源观测数据以及ERA5再分析资料对引发局地极端降水的中尺度对流系统(MCS)的演变过程与中尺度特征开展研究。(1) 此次强降水过程主要集中在凌晨时段，具有持续时间短、局地雨强极端、累积雨量大等特点，在3小时的降水过程中出现了两个降水峰值。(2) 这次过程为一次暖区暴雨过程，低层西南季风提供了充足的暖湿水汽，低涡切变线提供了良好的抬升条件。中α尺度季风云团呈准静止状态并升尺度增长为MCC(中尺度对流复合体)的过程引发了大湾区夜间局地的极端降水。(3) 过程中两个阶段的峰值降水与中γ尺度对流单体生消发展期间的传播与移动矢量发生的改变有密切联系。数个中γ尺度对流单体构成多单体风暴形态，呈西北-东南侧向排列，这些单体先后触发发展并有着各自的地面辐合线。对流单体在环境风引导下向偏东南方向移动引发第一阶段峰值降水。随后不同单体的辐合线连接，对流向西南方向传播显著加快，使对流系统移动矢量发生改变，因而造成第二阶段峰值降水。(4) 造成两段峰值降水的中γ尺度对流单体结构存在明显差异。第一阶段峰值降水的强回波延伸高度更高，具备倾斜、入流缺口和回波垂悬等类超级单体结构特征，第二阶段峰值降水回波则具有显著的热带对流低质心特征，造成了局地更极端的短历时强降水。

Abstract:

In the early morning of May 22, 2020, an extremely heavy rainfall process occurred in the Guangdong-Hong Kong-Macao Greater Bay Area. The maximum hourly and three-hour rainfall broke the historical record during the "Dragon Boat Water" period in Guangdong province. This paper uses multi-source observation data and ERA5 reanalysis data to study the evolution process and mesoscale characteristics of the mesoscale convective system (MCS) causing the local extreme precipitation. The results are shown as follows. (1) The heavy precipitation process mainly concentrated in the early morning hours, with the characteristics of short duration, extreme local rainfall intensity, and large accumulated rainfall. Two precipitation peaks appeared in the three-hour precipitation process. (2) This process is a torrential rain process in the warm sector. A low-level southwest monsoon provides sufficient warm and humid water vapor, and a low vortex shear line provides good uplifting conditions. The process of meso-α-scale monsoon cloud clusters was quasi-stationary and grew by upscaling into MCC, triggering the local nighttime extreme precipitation in the Greater Bay Area. (3) Two stages of peak precipitation in the process is closely related to the propagation of meso-γ-scale convective cells in the life cycle and the change of the motion vector. Several meso-γ-scale convective cells form a multi-cell storm pattern, which is arranged in the northwest-southeast lateral direction. These cells are triggered to develop successively and have their own ground convergence lines. The first stage of peak precipitation is caused by the convective cell moving to the southeast under the guidance of the ambient wind. Subsequently, the convergence lines of different cells are connected, and the propagation of convection to the southwest is significantly accelerated, which changes the movement vector of the convective system, thus causing the peak precipitation in the second stage. (4) There are obvious differences in the structure of the meso-γ-scale convective cells that cause the two periods of peak precipitation. The strong echoes of the peak precipitation in the first stage have a higher extension height with supercell-like structural characteristics such as inclination, inflow gap, and echo overhang, and the echoes of the second stage of peak precipitation are characterized by convective, low mass cores, causing more extreme and localized short-duration heavy precipitation.