弱垂直风切变条件下一次飑线大风的特征分析

Characteristic Analysis of Primary SquallLine Gales Under Weak Vertical Wind Shear

利用宣城市7个国家观测站及266个区域观测站观测数据、NCEP再分析、探空资料、风云卫星及宣城S波段多普勒雷达观测资料,分析2022年7月26日飑线过程。结果表明:1)该过程飑线系统发生在500 hPa高空槽附近,位于副高边缘,过程发生前宣城地区处于槽前及槽线附近,正涡度平流增强,之后高空槽过境,转为西北气流,干冷空气注入触发不稳定能量释放。2)探空资料显示飑线发展时段,层结为上干下湿,近地层有浅薄的逆温层,有利于能量的储存和触发,订正后超过4000 J/kg的对流有效位能和35℃以上的K指数说明能量条件非常好,而0~6 km垂直风切变只有14 m/s左右,说明此次过程是在强不稳定能量和弱切变环境下触发产生的。飑线后侧入流急流的动量下传及干冷空气的卷入促进了蒸发作用,从而形成强烈的下沉气流,促使冷池快速移动并引起地面大风。3)区域性10级雷暴大风的雷达特征明显:飑线过境前的弓形回波,中心强度55~60 dBZ,飑线前先后出现两条阵风锋快速移动,并在宣城站附近相遇触发对流再次加强。低层径向速度出现模糊,形成大片径向速度大值区。4)中层明显的径向辐合和风暴顶的强辐散都对地面大风有指示意义。

Using the observation data of 7 national observatories and 266 regional observatories in Xuancheng,NCEP reanalysis,radiosonde data,Fengyun satellite and S band Doppler radar observation data to analyze the squall line process on July 26,2022.The results indicate that:1)the squall line system of this process occurs near the 500 hPa high altitude trough,located at the edge of the subtropical high.Before the process,the Xuancheng area was in front of the trough and near the trough line,with an increase in positive vorticity advection.then,the high altitude trough passed through and it turned into a northwest airflow,and the injection of dry and cold air triggered the release of unstable energy.2)The radiosonde data shows that during the development period of the squall line,the stratification is dry at the top and wet at the bottom,and there is a shallow inversion layer near the stratum,which is conducive to energy storage and triggering.The corrected convective effective potential energy of more than 4000 J/kg and the K index above 35℃indicate that energy condition are very good,while the vertical wind shear at 0~6 km is only about 14 m/s,indicating that this process is triggered under the environment of strong unstable energy and weak shear.The downward momentum of the incoming jet stream behind the squall line and the involvement of dry and cold air promote evaporation,resulting in a strong sinking airflow,which promotes the rapid movement of the cold pool and causes strong winds on the ground.3)The radar characteristics of the regional level 10 thunderstorm gale are obvious:the bow echo before the squall line passes through,with a central intensity of 55~60 dBZ.Two gust fronts successively move rapidly in front of the squall line,and meet near Xuancheng railway station to trigger the convection to strengthen again.The radial velocity in the lower layer is blurred,forming a large area of radial velocity.4)The obvi-ous radial convergence in the middle layer and strong divergence at the storm crest both have indica-tive significance for surface strong winds.