Vortex processes in an idealized tornadic supercell

A high resolution idealized simulation of a tornadic supercell using the University of Wisconsin-Numerical Modeling System (UW-NMS) is presented. A multiple nested grid regime is used to increase horizontal resolution from 3 km on the coarsest grid (grid 1) to 40 m on the third nested grid (grid 4). We are able to produce a tornado on the second nested grid (grid 3) with 120 m horizontal resolution. A typical tornado may have width on the order of the resolution of this grid, which motivated us to understand how a tornado can be simulated with such coarse resolution. Investigating the idealized storm with our final nested grid, lead to the discovery of several robust vortex features that characterize a supercell thunderstorm. Here we present some of these coherent structures and vortex-on-vortex interactions that are found to be instrumental in the life cycle of a tornadic storm. The concept of superhelicity is introduced with application to studying the dynamics of supercells. It is suggested that traditional vorticity tendency and vortex line analysis of tornadogenesis be used alongside this new insight to provide a more complete approach to understanding the evolution of vorticity in these powerful storms.