一次干下击暴流的云微物理过程及移动和传播机制研究  

Study of the Cloud Microphysical Process and Mechanisms of Movement and Propagation of a Dry Downburst

作　　者：李彦辉 张飞民[1] 杨凯[1] 王澄海[1] LI Yanhui;ZHANG Feimin;YANG Kai;WANG Chenghai(Key Laboratory of Climate Resource Development and Disaster Prevention of Gansu Province(ACRE)/Research and Development Center of Earth System Model(RDCM),College of Atmospheric Sciences,Lanzhou University,Lanzhou 730000)

机构地区：[1]兰州大学大气科学学院/甘肃省气候资源开发及防灾减灾重点实验室/兰州大学地球系统模式研发中心,兰州730000

出　　处：《大气科学》2024年第5期2059-2079,共21页Chinese Journal of Atmospheric Sciences

基　　金：国家自然科学基金项目42175064、42275004;甘肃省重点研发计划项目23YFFA0001;中央高校基本科研业务费专项资金项目lzujbky-2024-ey08。

摘　　要：本文使用风廓线雷达、跑道自动观测及多普勒天气雷达等观测资料,对2020年5月14日半干旱地区兰州的一次弱天气尺度强迫下的干下击暴流(简称“5.14”)过程的发生和演变特征进行了分析;应用中尺度数值模式WRF(Weather Research and Forecasting)对该次过程的形成、移动及辐散出流区上空的水凝物演变特征进行了模拟,探讨了“5.14”过程外流传播的可能机制。结果表明:“5.14”过程的生命期约为30 min,云顶高度在9 km以上。在云体移向后侧3~6 km高度,同时出现突发性干冷空气急流侵入,云体断裂,云顶崩塌,动量下传和中低空1~4 km高度辐散出流急流,是下击暴流外流发生的可能原因。雪晶碰撞过冷云滴使之冻结合并,形成了下沉及外流区域的云中霰粒子均快速增长,模拟的霰粒子混合比在下击暴流暴发时增大了105倍;下沉区霰粒子加速了云中冷池的形成,是激发强下沉气流的原因之一。随着云体的移动,强下沉气流在地面上产生辐散出流,和相邻的辐散出流间交汇引起气流间的辐合上升运动,在云体移动方向前沿的下沉气流两侧形成两个气流上升区;随着干冷入流急流的深入,在云体移动方向激发出两个垂直环流,垂直环流由一支云内上升气流与一支紧邻的湿下沉气流相伴而成。垂直环流中的湿下沉气流在近地面形成冷池扩散促使了下击暴流的暴发,激发阵风锋。阵风锋向下击暴流辐散中心的外流方向扩散,阵风锋前的暖湿上升气流有利于新生单体合并进原风暴,风暴发展加强,随着阵风锋推进切断了暖湿上升气流导致重冷云顶下沉,云顶的不断上冲和崩溃形成了下击暴流的外流传播过程。阵风锋前的上升气流输送的雨滴粒子在0°C温度层附近冻结,冻结过程中释放的热量导致外流传播过程中0°C温度层不断升高,云中下沉的霰粒子融化层升高,融化后形成的雨滴粒子在下落过In this study,we conducted an analysis of the occurrence and evolution characteristics of a dry downburst event under weak synoptic forcing,hereinafter referred to as“5.14,”in the semiarid region of Lanzhou on May 14,2020.We used observational data from wind profile radar,runway automatic observation,and Doppler weather radar.We then employed the mesoscale numerical model WRF(Weather Research and Forecasting)to simulate the formation,movement,and evolution of the hydrocondensates over the divergence outflow area during the“5.14”event.Furthermore,we explored the potential mechanisms behind the outflow propagation of the“5.14”event.Our results revealed that the“5.14”event had a duration of approximately 30 min,with cloud tops reaching heights exceeding 9 km.Several factors were identified as possible causes of the outflow of the downburst,i.e.,the sudden intrusion of a dry cold air jet at altitudes of 3–6 km behind the moving cloud body,cloud body fracture,cloud top collapse,momentum downward transport,and the presence of divergence outflow jets at 1–4 km altitudes in the middle and lower atmosphere.During the event,snow crystals collided with supercooled cloud droplets,resulting in the rapid growth of graupel particles in both the sinking and outflow regions.Notably,the simulated mixing ratio of the graupel particles was found to increase by a factor of 105 during the initial outbreak of the downburst.The graupel particles in the sinking zone played a significant role in accelerating the formation of cold pools within the clouds,which contributed to the downdraft intensification.With the cloud body moving,the strong downdraft generated divergence outflow at the surface,causing the convergence and upward movement of airflow.This process resulted in the formation of two updraft areas on both sides of the downdraft,creating vertical circulations within the cloud.These vertical circulations comprised an updraft and a neighboring wet downdraft,which contributed to the spreading of cold pools near th

关 键 词：下击暴流 WRF模式 云微物理特征 移动和外流传播机制 

分 类 号：P458.3[天文地球—大气科学及气象学]