华北一次冷涡背景下飑线雷暴大风成因分析

Causal Analysis of a Squall Line Thunderstorm Gale under Background of a Cold Vortex in North China

利用NCEP再分析资料、地面和高空观测资料、卫星和雷达资料等,对风暴系统在华北中部加强发展为飑线并产生地面大风的原因进行了分析。结果表明:①2017年8月5日,在冷涡影响下,华北中高层有干空气渗透,具有条件不稳定层结,11:00天津订正探空CAPE高达3184J·kg^-1,且低层水汽充沛,有利于雷暴大风和湿对流的产生。②风暴出流边界与华北中部地面辐合线合并,且东南部地面露点更高,是飑线系统在华北中南部强烈发展的重要原因。③高温高湿环境使得风暴向南传播,在西偏北的引导气流作用下,最终风暴向南偏东方向移动。④北京探空0~6km垂直风切变达到3.3m·s^-1·km^-1,气流在前侧上升后侧下沉,强垂直运动与强垂直风切变作用产生了强旋转,使飑线系统初期具有中气旋特征。⑤中层强辐合和风暴顶辐散产生强下沉气流,地面最大风出现在中气旋发展阶段和冷池合并阶段。

By using the NCEP reanalysis data,conventional ground and radiosonde observation,satellite and Doppler radar data,etc.,the causes why the storm and ground wind strengthen in the central North China are analyzed in detail.The results show:(1)On 5 August 2017,under the influence of a cold vortex,there was dry air infiltration in the middle and upper levels and conditional instability in North China;at 11:00,according to the revised radiosonde data in Tianjin,the CAPE reached 3184 Jkg-1 and the lower level water vapor was abundant,which contributed to the occurrence of thunderstorm gale and moist convection.(2)The merger of the storm outflow boundary and the ground convergence line in the central North China and the higher surface dew-point temperature in the southeastern North China are important reasons for the strong development of the squall line system in central and southern China.(3)The high temperature and humidity environment made the storm spread southward,and under the guidance of the northwest airflow,the storm finally moved south by east.(4)At 08:00,according to Beijing radiosonde data,the vertical wind shear of 0 to 6 km reached 3.3 ms^-1 km^-1;the air flow rose in the front and sank in the back.Strong vertical motion and vertical wind shear produced strong rotation,which made the squall line system have the characteristics of mesocyclone in the early stage.(5)Strong convergence in the middle layer and divergence at the storm top produced violent downdrafts.The maximum wind on the ground occurred in the development stage of mesocyclones and the merging of cold pools.