暖区和锋面短时强降水的特征差异对比分析

Comparative Study on Differences in Characteristics between Short-Term Heavy Precipitation in Warm Regions and Fronts

文章利用常规观测资料、EAR5再分析资料和双偏振雷达资料,对比分析2023年7月25—27日四川盆地连续性暴雨过程中暖区和锋面降水阶段的形成机制、热动力条件和雷达偏振量特征,探讨暴雨的不同成因。研究结果表明:(1)25日暖区暴雨以热力强迫为主,盆地处副高边缘,低层θ_(se)可达358 K,大气不稳定性强,低层接近干绝热递减率形成了绝对不稳定层结,由地面辐合线触发对流;27日为锋面抬升与中尺度低涡系统共同作用形成强烈上升运动,形成持续性的对流降水,动力强迫明显,垂直速度达-4 Pa/s,而25日仅为-2.5 Pa/s。(2)25日ZDR最大达4 dB以上,KDP值为1.5 deg/km,具有雨滴尺寸大而浓度相对小的特点,27日ZDR为1~2.5 dB,KDP值达4.2 deg/km,雨滴尺寸稍小但密集,虽受热动力环境影响,雨滴性质存在区别,但两种情况均可导致雨强大。

With the help of conventional observation data,EAR5 reanalysis data and dual-polarization radar data,this paper aims to explore the formation,thermodynamic conditions and radar polarization characteristics of warm zone and frontal precipitation stages during the continuous rainstorm in Sichuan Basin from July 25 to 27,2023,so as to discuss the different causes of rainstorm.The research findings show that:(1)on the 25th,the rainstorm in the warm region is dominated by thermal forcing.The basin was at the edge of the subtropical high,with the low-level θ_(se) up to 358 K.The atmosphere is unstable,at the same time,the lower level is close to the dry adiabatic lapse rate,forming an absolutely unstable stratification,and the convection is triggered by ground convergence line;On the 27th,a strong upward movement was formed by the combined action of frontal uplift and mesoscale vortex system,resulting in continuous convective precipitation with obvious dynamic forcing.The vertical velocity reached-4 Pa/s,while it was only-2.5 Pa/s on the 25th.(2)On the 25th,the ZDR reached over 4 dB and the KDP value was 1.5 deg/km,which is characterized by large droplet and relatively low concentration.While on the 27th,the ZDR was 1-2.5 dB and the KDP value reached 4.2 deg/km,which is characterized by a slightly smaller but more dense droplets.In addition,droplet properties are affected by the thermal dynamic environment,but both can lead to strong rainfall.