Mesoscale Characteristics of a Squall Line on May 7,2023 in the Pearl River Delta Area

CAI Yiping; XIAN Xinghe; HUANG Chaoying; LI Chanzhu; YIN Shuxian

doi:10.3969/j.issn.1007-6190.2025.02.003

Abstract：This study attempts to analyze a squall line system from various aspects,including the weather background of its occurrence,the evolution of radar echoes,the microphysical characteristics within the squall line,and its mesoscale features.Using multiple observations from the regional automatic weather stations in Guangdong province,the ERA5-Interim reanalysis,a Doppler radar and a raindrop spectrometer,we analyzed a squall line that took place on May 7,2023 in the area of Pearl River Delta.The results are shown as follows.The squall line happened ahead of an upper-level shortwave trough and within a zone of low-level shear and convergence and a surface frontal zone.Prior to the squall line,the atmospheric stratifi-cation was marked with strong convective instability,a vertical structure that was dry at the upper level but moist at the low level,large vertical temperature lapse rates,and a moderate-to-high vertical wind shear.A dense se zone was continuously uplifted near a meso-β convergence line,and a convective system intensified to become a squall system.The propagation direction of the squall line interacted with the discontinuity boundary of low-level moisture,and the squall line strengthened to form a bow echo protruding forward.A rear inflow jet,a weak echo zone,a vertical echo structure at the upper and middle level,and a mesocy-clone were identified from the radar echo.The weather of extreme high winds took place on the south side of the mesocyclone,mainly caused by the effect of the rear inflow jet superimposed with the rotating mesocy-clone.The microphysical characteristic changes of the convective precipitation in the main body of the squall line were more pronounced than those in the stratiform precipitation of its rear portion.High-concentration and large raindrops were important causes of the short-range intense rainfall and heavy rainfall by this squall line.