台风山竹(1822)龙卷的双极化相控阵雷达特征

2018年9月17日台风山竹（1822）外围螺旋雨带中发生EF2级龙卷。在高湿度、高不稳定、强垂直风切变的环流背景下，龙卷在台风外围雨带上微型超级单体右后侧钩状回波顶端的弱回波区中发展起来。具有高时空分辨率的广州X波段双极化相控阵雷达，不仅观测到超级单体的发展过程，还呈现出龙卷涡旋演变特征:单体风暴尾端在右后方入流加强作用下，逐渐形成钩状回波形态，此时对流层中低层2~3 km高度附近的中气旋强度率先达到最大，随着旋转强度进一步加强和旋转中心高度逐步下降，低层强旋转特征越来越明显，当低层旋转速度达到峰值（超过21 m·s-1），旋转直径收缩到1 km范围，地面出现EF2级以上龙卷，旋转速度对区域出现清晰的弱回波龙卷眼区特征。X波段双极化相控阵雷达在龙卷观测中优势显著，弥补了多普勒天气雷达观测的不足。

Observation of A Tornado Event in Outside-region of Typhoon Mangkhut by X-band Polarimetric Phased Array Radar in 2018

It is well realized that the phased array radar provides fine information for meso-scale weather system, e.g., tornados. The detecting capability of Guangzhou X-band polarimetric phased array radar for severe storms is investigated, focusing on a violent tornado induced by a miniature supercell in the outer rain band of typhoon Mangkhut near Foshan on 17 September 2018 after Mangkhut's landfall. The rare complete typical tornado is captured, which is of category 2 on the enhanced Fujita scale (EF2), and it lasts for 23 minutes and causes great national economy loss.The structure, evolution and environmental conditions of the tornadic miniature supercell are discussed based on coastal Doppler S-band radar measurements. Environment conditions in the outer rain band are consistent with those of typhoon tornadoes in previous studies, with moderate convection effective potential energy and large shear below 3 km. S-band radar analysis indicate that this tornadic, miniature supercell exhibits characteristics similar to those found in landfalling hurricanes, including a hook echo, a small and shallow mesocyclone, and a relative long lifespan (~3 h).However, limited by beam blockage and resolution, further tornadic features are only observed by Guangzhou X-band polarimetric phased array radar. With the strengthening of inflow from right rear of the miniature supercell, hook echo is formed when the tornado occurs in the shallow and strong mesocyclone with the depth below the height of 2-3 km. It touches down when its parent circulation reaches its peak intensity of about 21 m·s-1. Along with intensifying of strength and contraction of couplet diameter, the height of the rotation declines below 1 km and characteristics of tornado vortex signature (TVS) are detected. The echo eye of weak echo region indicating the tornado eye is first observed. The X-band phased array radar shows great advantage in tornado observation, capturing some key characteristics of tornado evolution: Continually declining strong meso-cyclone and the appearance of TVS. The strengthening and deepening of TVS and the appearance of weak echo eye is highly likely to indicate the increase of tornado intensity. Data observed in the experiment and the preliminary results will be used in studies of tornado mechanism.