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.