极端持续性强降水过程雷达偏振量特征及演变

Characteristics and Evolution of Radar Polarization During Extremely Persistent Heavy Rainfall

为研究极端持续性强降水过程的中尺度结构和云物理特征,利用龙岩S波段双偏振雷达、雨滴谱仪、二维闪电定位仪等多源资料结合雷达风场反演方法,分析2022年5月26—27日福建一次极端持续性强降水过程。结果表明:该过程水汽充沛,不稳定能量适中,有利于产生强降水。强降水期间不低于45 dBZ的强回波主要集中在西南向喇叭口地形收缩处的山脉迎风坡一侧。强回波在气流辐合处持续发展,前两个阶段暴雨区西侧回波持续移入形成后向传播的列车效应;第3阶段强回波在东北风引导下向东偏南移动。该过程以海洋性对流降水和暖云降水为主,强降水主要由高浓度小尺度的雨滴粒子造成。第2阶段强烈上升运动在0℃层以上形成霰粒子,并与冰晶碰撞,产生负闪,冰相过程使霰粒子下落融化与低层雨滴的碰并增长形成大雨滴,降水效率高。降水粒子集中在气流汇合处,中低层存在高浓度雨滴粒子。差分反射率大值区多分布在中层上升气流处,大雨滴在下落过程中破碎为小雨滴,进一步加大雨滴粒子数。

Based on data of S-band dual-polarization Doppler radar,automatic weather station,disdrometer,2-D lightning locator and Doppler radar wind field retrieval method,mesoscale structure and cloud microphysical characteristics of an extremely persistent heavy rainfall occurred in southwest Fujian on 27 May 2022 are analyzed.Results indicate that the event takes place under the southwest flow on the south side of the low-level shear.Sufficient water vapor,moderate unsteady convective stratification,low lifting condensation height,and convective condensation height over the rainstorm area are all favorable for producing high-efficiency heavy rainfall.Strong echoes(no less than 45 dBZ)persist over the rainstorm area during heavy rainfall.The strong echo center is concentrated on the windward side of the mountain,located at the contraction of the topography of the trumpet opening to the southwest.The wind field retrieval shows that the strong echo persists for an extended period at the convergence of wind speed and the convergence of southerly and northerly airflow.During the first two stages,a strong echo continuously moves into the rainstorm area from the west,generating the train effect of backward propagation.In the third stage,the strong echo moves southeast under the guidance of northeast winds at the middle and upper levels.This process is dominated by oceanic convective rainfall and warm rain.Heavy rainfall is primarily composed of raindrop particles with high concentration and small scale.The lower layer is primarily composed of raindrop particles with high concentration and smaller scales.Raindrop particles in the middle layer are larger than those in the lower layer.Due to strong upward motion,negative flashes occur when graupel particles above 0℃layer collide with ice crystals during the second stage.Due to the ice phase process,large ice phase particles like graupel particles fall,melt,coalesce,and merge with smaller raindrops,resulting in the formation of larger raindrops and the production of highly efficient rainfall.The development of KDP above 0℃layer indicates an increase in rainfall,forecasting an advance of 6-20 minutes for the strengthening of relative surface ground rainfall.A large number of raindrop particles are primarily concentrated at the confluence of air currents.Hydrometeor accumulates here.The prolonged and intense echo causes the accumulation of water condensate over an extended period,ultimately causing heavy rainfall.There are high concentrations of raindrop particles in the middle and lower layers.The high value of ZDR is mostly concentrated in the middle layer updraft area.The high-value ZDR area and the high-value KDP area do not completely overlap.The distribution of ZDR is wider than that of KDP.Large raindrops break into small raindrops as they fall,increasing the number of raindrop particles.