2016年7月9日新乡暖区特大暴雨成因分析

Cause analysis of a warm-sector excessive heavy rainfall event in Xinxiang on 9 July 2016

利用常规气象观测资料、区域自动站资料、卫星云图和雷达产品及NCEP再分析资料,对2016年7月9日新乡暖区特大暴雨过程成因进行了综合分析。结果表明:该过程强降水持续时间长、强度大、分布不均匀、致灾严重,属暖区极端强降水,500 h Pa低涡和700 h Pa切变线是其主要影响系统;台风外围东南暖湿气流在太行山迎风坡(新乡西部)辐合抬升使特大暴雨区上空长时间维持深厚湿层,500 h Pa低涡南压所携带的弱冷平流与低层暖平流在新乡上空叠加进一步增加了大气层结不稳定,为暴雨发生提供了水汽和位势不稳定条件;200 h Pa显著分流区"抽吸作用"、太行山地形抬升和中低层低涡和切变线使新乡上空出现深厚垂直上升运动是暴雨形成的动力机制;华北中南部大范围高湿环境、深厚暖云层和湿层以及异常偏低的自由对流高度和抬升凝结高度与中等偏强的对流有效位能,是导致新乡高降水效率的有利条件;新乡强降水中心由2个孤立的β中尺度对流系统(MβCS)合并造成,其系统内部若干低质心对流单体则由太行山东侧山前长时间维持的中尺度辐合系统产生;雷达反射率因子反映出低质心暖云降水回波特征,强回波列车效应明显,新乡特大暴雨由积云(对流)为主的积层混合降水回波长时间滞留造成。

Using conventional meteorological observations,observational data from regional automatic weather stations,satellite images,radar data and NCEP reanalysis data,we have conducted a synergic analysis of the cause of a warm-sector excessive heavy rainfall event in Xinxiang on 9 July 2016.The results indicate that this event falls into the category of warm-sector extreme precipitation,and is long in precipitation duration,high in intensity,inhomogeneous in distribution and serious in disaster,whose main weather systems are 500 h Pa low vortex and 700 h Pa shear line.The southeast warm and wet airflow on the periphery of a typhoon was uplifted at the windward side(western Xinxiang) of the Taihang mountains,which made the deep moist layer over the heavy rain area maintaining for a long time.The superposition of the weak cold advection carried by the low vortex moving southwards at 500 h Pa and the warm advection in the low-level over Xinxiang further increased atmospheric instability,which provided water vapor and potential instability conditions for the occurrence of heavy rainfall.Suction effect in the significant diversion area at 200 h Pa,topographic uplift effect by Taihang mountains,and low vortex and shear line in the midand low-level caused the vertical upward movement over Xinxiang,which is the dynamic mechanism for heavy rainfall formation.Favorable conditions for high precipitation efficiency in Xinxiang include large-scale high humidity environment in the central and southern part of North China,thick warm cloud and humid layers,abnormally low free convection height and lifting condensation height as well as medium to strong CAPE value.The heavy precipitation center in Xinxiang was caused by the merging of two isolated β-mesoscale convective systems(MβCS) within which several low-mass center convective cells were generated by a mesoscale convergence system maintained in the east front of Taihang Mountain for a long time.The low-mass center warm cloud precipitation echo and the obvious train effect can be found in the radar basic reflectivity factor chart.It is the long-time retention of mixed convective precipitation echoes dominated by convective echoes that caused the excessive heavy rainfall event in Xinxiang.