西北东部半干旱区一次极端特大暴雨的触发和维持机制  

Mechanism of trigger and maintenance during an extremely torrential rain in semi-arid region of eastern Northwest China

作　　者：沙宏娥 傅朝[1] 刘维成[1] 徐丽丽 刘娜 刘新雨 马绎皓 SHA Honge;FU Zhao;LIU Weicheng;XU Lili;LIU Na;LIU Xinyu;MA Yihao(Lanzhou Central Meteorological Observatory,Lanzhou 730020,China;Jiuquan Meteorological Bureau of Gansu Province,Jiuquan735008,Gansu,China)

机构地区：[1]兰州中心气象台,甘肃兰州730020 [2]甘肃省酒泉市气象局,甘肃酒泉735008

出　　处：《干旱气象》2022年第6期933-944,共12页Journal of Arid Meteorology

基　　金：甘肃省气象局气象科研项目重点项目(Zd2023-03);甘肃省气象局创新团队项目(GSQXCXTD-2020-01);甘肃省气象局气象科研面上项目(Ms2021-07)共同资助。

摘　　要：2022年7月15日地处西北东部半干旱区的甘肃庆阳出现特大暴雨,多站日雨量和小时雨量均突破历史极值,利用多源观测资料和ERA5再分析资料,针对这次特大暴雨过程形成机制进行分析。结果表明,本次过程是发生在黄土高原复杂地形下弱天气尺度斜压强迫、弱不稳定能量及深厚湿层背景下的暖区暴雨,局地性强、强降水持续时间长;南亚高压、副热带高压及低层气压系统上下叠加的环流形势配置有利于中尺度对流系统发生发展;地面辐合线和偏南低空急流触发对流系统初生、发展,低空急流的发展和长时间维持使地面辐合线不断加强,同时急流左侧(暴雨区)与其出口区和入口区右侧形成的稳定次级环流是对流系统维持的关键,而凝结潜热释放引发的局地锋生、低层正涡度发展则是对流系统发展维持的另一重要因素,同时也是大气不稳定度维持的重要原因。中尺度对流系统呈现深厚低质心、准静止特征,雷达回波具有后向传播和列车效应特征。A torrential rain struck Qingyang on July 15,2022,which is located in semi-arid region of eastern Northwest China,causing the daily rainfall and hourly rainfall at several stations to exceed the historical extreme values.The formation mechanism of the torren⁃tial rain in semi-arid region of Northwest China is analyzed based on multi-source observation data and ERA5 reanalysis data,so as to provide some useful reference for rainstorm forecast in arid and semi-arid areas.The results show that the torrential rain process oc⁃curred under the background of weak synoptic scale baroclinic forcing,weak unstable energy and deep wet layer in the complex terrain of the Loess Plateau,with characteristics of strong locality and long duration of heavy precipitation,which is a warm-sector torrential rain.The special circulation configuration of South Asian high,western Pacific subtropical high and pressure system at the lower level is conducive to the occurrence and development of mesoscale convective system.Convective initiation and development were triggered by surface wind convergence line and low-level southerly jet.Development and long-time maintenance of the low-level jet intensified surface convergence line continuously.The left side of low-level jet(rainstorm area)formed two stable secondary circulations with the right side of the exit and entrance of it,respectively,which is the key factor for the maintenance of the convective system.The release of condensation latent heat caused local frontogenesis and low-level positive vorticity development,which is another important factor for development and maintenance of convective systems,and it is also an important reason for maintenance of atmospheric instability.The mesoscale convective system exhibited deep,low center of mass and quasi-stationary characteristics under the combined effects of the above mentioned factors,the radar echoes were characterized by backward propagation and train effect.

关 键 词：西北东部半干旱区 暖区特大暴雨 触发维持机制 低空急流 次级环流 

分 类 号：P458.2[天文地球—大气科学及气象学] P458.3