Near-Surface Vorticity Generation in Tornadic and Non-Tornadic Simulated Supercells

An idealized three-dimensional model (CM1) is used to simulate and study near-surface vorticity generation in both tornadic and non-tornadic supercells at tornado resolving grid spacing (dx=100 m). The simulations are initialized with a subset of RUC-2 supercell proximity soundings from both non-tornadic and significantly tornadic supercells. The supercell simulation dataset consists of twenty-one that produce tornado-like vortices (from the significantly tornadic sounding class) and fourteen that do not (from the non-tornadic sounding class). Tornado presence in these simulations was determined using an automated detection algorithm based on Rankine vortex theory.

Circulation and trajectory analyses were performed to determine differences in low-level airflow between the tornadic and non-tornadic simulations. Questions to be addressed in this study include: (a) what is the most common source region of near surface vertical vorticity in the tornadic cases; (b) what is the relative importance of baroclinic and barotropic vertical vorticity; (c) what is the most common tornadogenesis failure mechanism in the non-tornadic simulations; and (d) what are the most important parameters that discriminate between environments of simulated tornadic and non-tornadic supercells?