关中北部一次暴雨水汽条件及不稳定分析  

Water Vapor Condition and Instability Analysis of a Rainstorm in Northern Guanzhong

作　　者：郭大梅[1] 潘留杰[1] 李明娟[1] 屈丽玮[1] 史月琴[2] 张黎[1] GUO Damei;PAN Liujie;LI Mingjuan;QU Liwei;SHI Yueqin;ZHANG Li(Shaanxi Meteorological Observatory,Xi’an 710014,Shaanxi,China;Chinese Academy of Meteorological Science/Weather Modification Center of China Meteorological Administration,Beijing 100081,China)

机构地区：[1]陕西省气象台,陕西西安710015 [2]中国气象科学研究院/中国气象局人工影响天气中心,北京100081

出　　处：《高原气象》2022年第6期1481-1491,共11页Plateau Meteorology

基　　金：陕西省自然科学基础研究计划项目(2021JM-595);中国气象局数值预报(GRAPES)发展专项;国家重点研发计划项目(2018YFC1507901)。

摘　　要：2019年9月13-14日关中北部出现暴雨天气,这次暴雨开始时关中北部地区位于冷锋后地面冷高压中和700 hPa横切变线的北侧,探空图上中低层是锋面逆温稳定层结,中低层以下是深厚的冷垫,地面能量较低,没有对流不稳定,低层水汽不足,短期时效内暴雨漏报。为了研究此次过程中的水汽条件和不稳定机制,为今后此类暴雨预报提供有价值的预报思路,利用常规地面高空观测、欧洲中心细网格模式预报等资料对其水汽条件和不稳定进行诊断分析,结果表明:较强降水期间关中北部水汽的大值区集中在700 hPa,700 hPa随时间而增强的偏南风为其提供了充沛的水汽,700 hPa比湿大值区、切变线随着增强的偏南风北移至关中北部,这为关中北部暴雨提供了较强的水汽辐合条件,因此,为关中北部提供充沛水汽的偏南风能否随时间而增强是其暴雨能否发生的关键。而偏南风增强与高低空急流的耦合和凝结潜热释放有关,暴雨区高低空急流耦合形成的次级环流上升支有利于暴雨区中低层减压,西太平洋副热带高压和暴雨区之间的气压梯度加大,这将使西南低空急流加强并向东北方向移动,移动后的低空急流在其前方辐合上升造成新的暴雨区,这将形成低空急流和暴雨的正反馈,西南低空急流随着时间向东北方向移动,造成关中南部地区出现低空急流和关中北部偏南风增强;暴雨区凝结潜热释放有利于上升运动,使得中低层减压,这同样造成关中南部形成偏南风急流、关中北部偏南风增强。可见,高低空急流耦合和凝结潜热释放通过影响偏南风而间接影响关中北部暴雨区水汽条件。关中北部暴雨的不稳定机制是条件性对称不稳定。700~600 hPa关中北部暴雨区有着较强的垂直地转风切变和向北的水平地转风切变使得等地转绝对动量倾角较小,偏南暖湿气流输送水汽和能量使得等饱和相当位温Conventional observation and EC-thin data are used to analyze the forecasting difficulties of a severe rainstorm event on 14 September 2019 in northern Guanzhong. Results show that the rainstorm occurred in the process of trough a loft moving eastwards and the Western Pacific subtropical high receding southeastwards. At initial stage of rainstorm,northern Guanzhong lies in the cold high 240~300 km behind the cold front on surface,on the north side of the transverse shear on 700 hPa level. The sounding graph demonstrates a stable stratification of frontal temperature inversion on lower-middle level with a deep cold pad below,lack of water vapor on lower level,and low energy on surface. The 1-hourly peak rainfall accumulation is 7 mm during the entire rain process obtained by national observation station,which doesn’t fall in convective torrential rain,but frontal rain caused by the cold front continuously for a certain time. Analyzing water vapor in northern Guanzhong,it is found that a large value area of water vapor is concentrated on 700 hPa level during the heavy rainfall episode.The southerly wind on 700 hPa level strengthened over time brings it with plenty of water vapor,and drives a large value area of specific humidity and the shear line northwards to northern Guanzhong,which provides strong water vapor convergence conditions for the rainstorm. Therefore,whether the southerly wind over northern Guanzhong can increase over time is the key to the occurrence of the rainstorm. The coupling of upper-lower level jets and the release of latent heat of condensation are two important factors affecting southerly wind over northern Guanzhong. The ascending branch of the secondary circulation formed by the coupling of upper-lower level jets is favorable for depressurization on mid-low levels over the rainstorm area. The increase of pressure gradient between the western Pacific subtropical high and the rainstorm area will strengthen the lower-level southwesterly jet and drives it northeastwards. The enhanced lower-l

关 键 词：暴雨 偏南风 高低空急流耦合 凝结潜热 条件性对称不稳定 

分 类 号：P441[天文地球—大气科学及气象学]