西安连续两天短时暴雨的对流条件及触发机制对比分析  

Comparative Analysis of Convective Conditions and Triggering Mechanisms of Short-term Rainstorm in Xi'an on Two Consecutive Days

作　　者：赵强[1,2] 王楠 高星星[1] 陈小婷 ZHAO Qiang;WANG Nan;GAO Xingxing;CHEN Xiaoting(Shaanxi Meteorological Observatory,Xi'an 710014,Shaanxi,China;Key Laboratory of Eco-Environment and Meteorology for the Qinling Mountains and Loess Plateau,Xi'an 710016,Shaanxi,China)

机构地区：[1]陕西省气象台,陕西西安710014 [2]秦岭和黄土高原生态环境气象重点实验室,陕西西安710016

出　　处：《高原气象》2021年第4期801-814,共14页Plateau Meteorology

基　　金：秦岭和黄土高原生态环境气象重点实验室开放研究课题(2019Z-1);中国气象局预报员专项(CMAYBY2019-116)。

摘　　要：2015年8月2-3日西安地区连续两天出现了短时暴雨天气,引发山洪和泥石流,造成铁路中断和人员伤亡。本文利用常规观测资料、卫星云图及西安站的多普勒雷达资料、欧洲中期天气预报中心(ECMWF)再分析资料(0.25°×0.25°),对两次过程的对流条件和触发机制进行对比分析。结果表明:两天的对流条件有明显区别,2日西安为副热带高压(简称副高)控制,高温高湿,地面温度达39℃,能量充沛,对流有效位能(CAPE)值大于2000 J·kg^(-1),地面到850 hPa大气垂直温度递减率接近超绝热状态,非常利于对流触发;3日高原槽东移,西安位于低槽和副高之间冷暖空气交汇区,地面上陕北有冷锋南压,近地面层不稳定度降低,低层冷平流比2日有明显增强,地面温度降至30℃,CAPE值800 J·kg^(-1)。对比来看,3日气温、不稳定能量较2日有显著降低,但天气尺度系统强迫更强。触发机制分析显示:2日下午地面辐合线在延安触发对流,向南移动过程中产生冷池,出流的阵风锋在西安触发新生对流,由于西安地区水汽含量大,能量充足,对流回波维持时间长,产生短时暴雨,1 h降水量高达47.2 mm,而3日下午的暴雨是由冷锋触发,强锋生区域与低层冷平流区域对应较好,位于近地面层到850 hPa,锋生次级环流诊断发现,地面到850 hPa由于锋生造成的垂直运动,使得气块克服对流抑制抬升到自由对流高度,触发不稳定能量释放,产生强降水,冷锋南压过程中由于秦岭的阻挡作用,在沿山北麓边界层形成急流,沿着急流强雷暴单体不断生成并在向东移动过程中形成列车效应,造成山区的大暴雨。Using conventional observation data,satellite cloud images,doppler radar data of Xi'an station and ECMWF reanalysis data(0.25°×0.25°),the convective environmental conditions and triggering mechanism of two short-term rainstorms which occurred in Xi'an on 2 and 3 August 2015,causing flash floods and mudslides and resulting in railway interruption and casualties were comparative analyzed.Results show that atmospheric environment conditions are obviously different.Xi'an is controlled by subtropical high,has high temperature and humidity and ground temperature reaches 39℃,CAPE value is more than 2000 J·kg^(-1).The decline rate of vertical temperature from ground to 850 hPa is close to superadiabatic state,which is very conducive to the triggering of convection on 2 August 2015.However,on 3 August 2015,Xi'an is located at the intersection of cold and warm air between the trough and subtropical high.There is a ground cold front moving southward in northern Shaanxi and air instability near surface layer decreases.Cold advection is stronger and ground temperature drops to 30℃,CAPE value is 800 J·kg^(-1).The synoptic scale system forcing is stronger on 3 August,although the temperature and unstable energy are significantly lower than those on 2 August.From the perspective of triggering mechanism,the surface convergence line triggers convection in the afternoon of 2 August in Yan'an and produces cold pool in the process of moving southward.The gust front of outflow triggers new convection,due to the large water vapor content and sufficient energy around Xi'an area,short-term rainstorm is generated and hourly precipitation is as high as 47.2 mm.However,the rainstorm in the afternoon of 3 August is triggered by cold front.Strong frontogenesis area corresponds well with the low-level cold advection area,which locates in the near-surface layer to 850 hPa.Diagnosis result indicated that vertical movement from ground to 850 hPa caused by frontogenesis secondary circulation makes the air mass overcome convective inhibiti

关 键 词：短时暴雨 大气不稳定度 阵风锋 冷锋 锋生次级环流 

分 类 号：P458.2[天文地球—大气科学及气象学]