Numerical Simulation Study Of Supercell Storm And Tornado In Funing Tornado In 2016

An EF4 supercell tornado occurred on 23 June 2016 in Funing,Yancheng City,Jiangsu Province,which was the second EF4 tornado in Jiangsu Province since 1950 and resulted in99 deaths and 846 injuries.This paper uses the ARPS(Advanced Regional Prediction System)model to simulate this tornado.Four one-way nesting forecast experiments are run,with the horizontal grid spacing of 9000,1000,250,75 m,respectively.The experiments on 75-m grid reproduce an EF4 tornado successfully,which lasts about 40 min,but the tornado simulated,comparing with the real,is 25 km northward and delayed about 30 min.The influence of radar data assimilation and Drop Size Distributions(DSD)on tornado and tornadic storm simulation is tested through sensitivity experiments,and the three-dimensional structure of the tornado and tornadic storm is analyzed with the 75-m model data,and the vorticity budget is diagnosed by the vorticity equation.The main conclusions are as follows:(1)The tornadic supercell with a clear structure and obvious hook echo characteristics can be simulated on the 1-km grid,but some structure characteristics under Meso-? scale like tornadic vortices or tornado-like vortices(TLVs)cannot be simulated until the horizontal resolution is improved further.Only TLVs,whose structures evolved from “one-cell” to “two-cell”,can be simulated on 250-m grid,and have weaker intensity than that of tornadic vortices.The tornadic vortices simulated on 75-m grid develop from “one-cell” to “two-cell” and finally to “multi-vortex” structures.(2)Radar data assimilation has a positive impact on simulations of tornadic storms.The environmental conditions of tornadic storm occurrence,in terms of thermodynamics and dynamics,are improved by assimilating radar reflectivity and radial velocity,which produce a tornadic storm and strong low-level mesocyclone earlier.(3)The adjustment of DSD has a significant impact on the scope and intensity of the cold pool,but little on the environmental flow.When the cold pool is of proper strength,a balance exists between the cold pool outflow and low-level inflow,which leads to relatively consistent movement of the low-and middle-level gust front and small tilt of the front,and a near-vertical alignment between low-and middle-level mesocyclone;and the gust front moves steadily with the mesocyclone and provides a stable and vertical updraft for the mesocyclone,which enhances the suction of mesocyclone on low-level vortex and is beneficial to tornadogenesis.(4)For the genesis mechanism of tornadic vortex,the tornado vortex is initially generated by combining a series of strong small vortices produced by Forward-Flank Gust Front(FFGF),Rear-Flank Gust Front(RFGF)and the secondary outflow of Rear-Flank Downdraft(RFD).In this process,the convergence of vortices combination and the strong updraft it caused,play an important role in the enhancement of tornado vortex.After the combination of vortices,the convergence caused by secondary outflow gust front strengthens the intensity of tornadic vortex further.