三门峡地区一次飑线天气成因及特征分析

Analysis of Characteristics and Causes of a Squall Line Weather in Sanmenxia

2013年7月31日20时-8月1日08时,三门峡地区出现了一次飑线天气过程。对本次过程高低空天气形势、卫星资料、NCEP再分析物理量、雷达产品等资料的分析结果表明:这次飑线天气过程是在上干冷下暖湿的不稳定大气层结条件下产生的,地面辐合线是这次飑线产生的触发机制;飑线发生前热力不稳定层结的存在和中低层的正涡度区、高层的辐散区,对预报强对流天气有一定指示作用;飑线天气发生在Tbb梯度最大区。从雷达回波看,这次飑线过程分为生成、旺盛和消散三个阶段。东西方向飑线由对流单体合并而成,在移动过程中,受中条山地形抬升和黄河湿热河面影响得到发展和增强;南北方向飑线由上游陕西东移过来,受低层强的偏西急流影响形成弓形回波;两个飑线合并成"人字形"共同影响三门峡地区。在飑线旺盛阶段,雷达回波存在低层有界弱回波区和中高层悬垂回波结构,冰雹发生在南北向飑线(弓形回波)后侧;两条飑线回波合并处出现明显的中气旋特征,是产生局地强降水的有利条件。

A squall line weather appeared during the period from 20：00 31th July to 08：00 1st August 2013 in Sanmenxia. The analysis results of high-low altitude synoptic situation, satellite images, NCEP reanalysis physical quantities and radar products showed that the squall line weather process was generated in unstable stratification, in which it was dry and cold at the upper level, wet and warm at the lower level, and it was triggered by surface convergence line ; the unstable thermal stratification, middle low level positive vorticlty and high-level divergence area happened before the squall line weather could be indicators of strong convective weather forecast; the squall line weather occurred in the Tbb gradient maximun regions. According to the radar echo, the squall line process was divided into generating, flour- ishing and dissipating stages. The merging of convective cells formed the west-east squall line which was developed and enhanced by the lifting of Zhongtiao mountains topography and the influence of warm-wet surface of the Yellow river when moving forward; the north-south squall line moving eastward from Shaanxi, it was affected by westward low-level strong jet, and formed bow echo; the above two squall lines merged into ＂ chevron＂, and influenced Sanmenxia area. When the squall line was at vigorous stage, in radar echo there are bounded weak echo region in the lower level and overhang echo structure in the mid-high level, the hail occurred in the back of north-south squall line （bow echo） ; obvious mesocy- clone characteristics appeared in the joint area of the two squall lines＇ echo, which is a favorable condition of heavy rainfall.