An Investigation of the Formation, Structure, and Evolution of a Rare EF4 tornado in East China using a High-Resolution Numerical Simulation

Devastating tornadoes in China have received more attention in recent years. Most of them have developed within the East Asia monsoon regime, with an environment quite different from tornadoes in the U.S. A rare EF4 tornado claimed 99 lives on 23 June 2016 in Funing, Yancheng. An idealized, high-resolution (25-m horizontal grid spacing) numerical simulation of a supercell thunderstorm was initialized with the environment near the deadly tornado. The simulated storm develops a violent tornado, with winds exceeding EF4 in strength. The tornado persisted for more than 10 min, was accompanied by a funnel cloud that extended to the surface, and exhibited a double-helix vorticity structure. One of the interesting findings of this work is that a violent surface vortex, accompanied by intense radial inflow and a corner region, was able to be generated and maintained even though the simulation employed a free-slip lower boundary condition [the boundary condition was that of Klemp and Wilhelmson (1978), in which the shear stress at z=0 was set to the stress at the first interior grid point, as opposed to a zero-stress boundary condition]. In addition to vortex characteristics, the presentation will discuss the key processes that lead to tornadogenesis. The success of this simulation (the simulated and observed storms had many striking similarities), despite the limited data and idealized simulation approach, is encouraging in that additional studies of historical tornadoes in China may be possible.