The effects of low-level stability and nonlinear vortex interactions on tornadogenesis

In supercell thunderstorms, vortices of many spatial scales are present in the vicinity of the low and mid-level mesocyclones. For statically neutral environments, nonlinear vortex-vortex interactions have been shown lead to alignment of vortices in the direction of the weighted average vorticity of the merging vortices. Both the precessional timescale and final vorticity vector are shown to depend on the relative size and strength of the interacting vortex features. The properties of these interactions are consistent with vortex interactions observed during tornadogenesis, leading us to the overarching hypothesis of this study that barotropic (or turbulent) realignment is potentially an important mechanism of tornadogenesis.

The theoretical foundation for vortex interaction will be given at the oral presentation. Then, a simplified relationship for the case of a strong vertical vortex strengthening through the absorption of smaller scale, randomly oriented turbulent (barotropic) vortices will be presented. It will be shown that, such vortex interactions become increasingly muted in the presence of stronger static stability, which subdues the free inertial precession of vortical features. These findings also lead to an alternative explanation for the failure of tornadogenesis in cases where the downdraft induced stabilization of the boundary layer exceeds a critical level.