2023年4月18日厦门暖区特大暴雨中尺度特征及低空急流的作用

Mesoscale characteristics and role of low-level jets in a warm-sector severe torrential rain event in Xiamen on 18 April 2023

2023年4月18日厦门遭遇入汛以来最强暖区暴雨过程,过程具有降水强度大、局地性强等特点。利用常规观测资料、地面自动站观测资料以及双偏振雷达、风廓线雷达、雨滴谱仪等新型探测资料对此次暴雨的天气背景、中尺度对流系统发展演变及低空急流在其中的作用进行了分析,结果表明:(1)此次暖区暴雨主要影响系统为偏南风天气尺度低空急流和东南风边界层急流,其强烈发展增强了局地的水汽及不稳定条件;(2)低质心的线状中尺度对流系统(MCS)嵌有类超级单体风暴在低空急流左侧辐合区内形成发展,MCS在福建南部沿海长时间维持,形成“列车效应”导致厦门极端强降水的发生;(3)类超级单体风暴强回波区差分反射率因子(ZDR)、差分传播相移(KDP)与相关系数(CC)均较大,质心低于经典超级单体风暴。此外,强降水云具有高浓度的小雨滴与大雨滴并存的暖区暴雨云微物理特征。(4)低空急流迅速增强和向下扩展与强降水密切相关,双低空急流耦合产生的上升运动是此次暖区暴雨主要的天气尺度触发机制。

An extremely warm-sector severe torrential rain event occurred in Xiamen on 18 April,2023,characterized by high intensity,strong locality and hard to predict.The synoptic background,mesoscale characteristics and the role of low-level jets were analyzed using multi-source detection data such as conventional observation data,automatic meteorological stations data,dual polarization Doppler radar,wind-profile radar and disdrometer.The results are as follows.(1)The southerly synoptic-system-related low-level jet(SLLJ)and southeasterly boundary layer jet(BLJ)are the main influence systems,whose significant development improved local water vapor and instability conditions.(2)The linear mesoscale convective system(MCS)embedded with quasi-supercell storm,formed and developed in the left side of the low-level jet.It has been maintained for a long time along the southern coast of Fujian,exhibiting low echo centroids and high precipitation efficiency.This combination causes severe torrential rain due to the“train effect”.(3)The ZDR,KDP,CC are all large in the strong echo area of the quasi-supercell storm,with a lower centroid height compared to the classical supercell storm.High concentrations of small and large raindrops are the main cloud microphysical characteristics of warm-sector torrential rain.(4)The rapid intensification and downward expansion of the low-level jet is closely related to heavy rain,and the ascending motion produced by the coupling of the double low-level jets was the main synoptic-scale triggering mechanism for this warm-sector heavy severe torrential rain.