【摘要】 利用常规观测资料、NCEP/NCAR再分析资料以及卫星云图、多普勒雷达探测等资料,对2008年7月22日梅雨锋西段襄阳特大暴雨成因进行诊断分析。结果表明:1)"鞍"型大尺度环流配置下,沿副热带高压西北侧北上的西南暖湿气流与东北低涡后部南下的变性干冷空气交汇于江淮—汉水流域,形成以边界层湿度梯度为主要特征的准静止锋面系统,为襄阳特大暴雨形成、发展提供了有利条件;2)随着高原槽东移、西南低涡发展,襄阳附近锋生加强,在充足的水汽和弱的热力不稳定层结条件下,边界层锋生和与之相联系的高空急流右后侧强辐散耦合可能是襄阳强降水发生发展的主要动力机制;3)特大暴雨的发生与其北侧超低空东北风急流和南侧南风急流之间辐合的加强有密切关系,边界层锋生加强也与干湿两支气流发展有关,雷达观测表现为弱而宽的回波带变窄、强度增大;4)汉江上游地区的喇叭口地形和中游地区的峡谷通道也可能是有利于南北风超低空急流在襄阳交汇产生强锋生的重要原因;5)边界层水汽通量辐合中心与强降水中心吻合,对降水定点预报具有很好的指示意义。更多还原

【Abstract】 Diagnostic analysis on a severe torrential rain along the west section of Meiyu front in Xiangyang,Hubei province on 22 July 2008 was made by using conventional observation data,reanalysis data from NCEP/NCAR,satellite images and Doppler-Radar data etc.The main results are as follows.Against a background of the saddle pattern disposition,southwest warm and wet airflow moving northwards along the northwest of subtropical high conflicted with indifferent dry and cold air moving southwards along the rear of northeast vortex in the Yangtze-Huaihe River and Han River region forming the quasi-stationary frontal system with the features of moisture gradient in boundary layer,which provided beneficial conditions for the formation and development of torrential rain in Xiangyang.The frontogenesis near Xiangyang was reinforced with the plateau trough moving eastward and the southwest vortex developing.The coupling of frontogenesis in boundary layer and its associated strong divergence in the right-rear of high-level jet may be the main dynamical mechanism of severe precipitation in Xiangyang with the sufficient water vapor and the weak unstable thermodynamic stratification.Emergence of the torrential rain was closely connected with the reinforcement of convergence between the ultra-low-level northeasterly jet in north of the torrential rain and the southerly jet in south of the torrential rain,and the reinforcement of frontogenesis in boundary layer was closely connected with the development of a dry airflow and a wet airflow.Radar detections showed that the radar echo band became narrow and strong.Trumpet shaped topography in the upper Hanjiang River and the gorge channel of the middle Hanjiang River contributed to the confluence between southerly jet and northerly jet in ultra-low-level in Xiangyang,and this is the possible reason which leads to severe frontogenesis.The convergence center of water vapor in boundary layer was corresponding with the severe precipitation center,which had a certainly prediction significance for the fixed-point precipitation forecast.更多还原