传播运动在对流风暴合并过程中的作用

2012年8月18日下午,山东省境内飑线在形成过程中发生多次合并,强度增强,造成章丘和宁阳分别出现9级和10级雷暴大风。基于多普勒天气雷达反演风场和地面加密自动气象站资料,分析了传播运动在对流风暴合并过程中的作用。结果表明:1)地面冷池前沿阵风锋强度大,垂直厚度达2 km。受其影响,飑线向东移动的同时向东传播(前向传播),北段逐渐演变为弓形回波。2)弓形回波与单体E分别具有独立的垂直环流,均为前向传播,但位于上游的弓形回波传播速度快,二者最终合并,垂直环流合二为一。3)弓形回波与单体E合并过程中,水平风速与上升运动明显增大,气压降低,尺度减小,最终形成强烈旋转上升的小尺度低气压柱,造成章丘大风。4)飑线尾部水汽充沛,阵风锋辐合造成飑线前侧的暖湿空气抬升,不断产生新的对流单体并逐渐合并增强,导致飑线向西南方向传播(后向传播)。5)位于下游的对流单体传播方向与平流方向相反,在3 km高度产生云桥,最终与上游单体整层合并。飑线尾部对流风暴多次合并,强度持续增强,造成宁阳大风。

Effect of propagation moving on the convective storm mergence process

There have previously been many mergences during the squall line formation process,after which its intensity enhanced and caused 9-and 10-scale thunderstorm gales in Zhangqiu and Ningyang in Shandong Province in the afternoon of 18 August 2012.Based on the retrieved wind from Doppler weather radar and automatic weather station(AWS) data,this paper analyzes the effect of propagation moving on the convective storm mergence during the squall line developmental process.The results show the following:1)The gust front prior to the surface cold pool was intensive,its vertical thickness reached up to 2 km,under its influence the squall propagated eastward while moving eastward(forward propagation),and the north of squall line changed to bow echo.2)The bow echo and cell E both possessed independent vertical circulations,and all propagated forward.The propagation velocity of the squall line located upstream was faster than that of the cell E,thus they emerged in the end and their vertical circulation combined.3)During the mergence process,the horizontal and upward wind speed were all significantly increased,and the pressure in the air column was reduced.Under the influence of pressure gradient force,a small scale low pressure column with strong rotating updrafts was formed,after which thunderstorm gales were produced in Zhangqiu.4)Due to the fact that there was abundant vapor present in the end of the squall line,the warm and moist air were lifted by the gust front,so that new cells were produced continually and their strength increased in the case of mergence,resulting in the squall line propagating southwestward(back propagation).5)The downstream convective cells propagated in the opposite direction of the advection direction,generating a cloud bridge at a height of 3 km,and eventually merged with the upstream cells.The convective storms at the tail of the squall line merged several times,and the strength continued increasing,thereby causing the Ningyang thunderstorm gales.