Supercell vorticity: structures and vertical communication mechanisms

A high-resolution numerical simulation of the well-known Goshen County, Wyoming storm was compared with observational data collected during the VORTEX II field campaign. Idealized supercell simulations were also run to provide perspective on the robustness of the key features of these storms. A rich spectrum of vortex structures, processes and interactions were evident. These include vortex sheets, which given an instability undergo a roll-up process that was found to be critical in rearranging and locally concentrating vorticity. Vortex-vortex interactions, including (three dimensional) coiling and braiding tubes are ubiquitous in these simulations. Many vortex structures and processes identified are already well understood by the fluid dynamics community, but have been largely overlooked in regard to tornadogenesis. Possibly the most important outcome from our initial simulations is the understanding that the upper levels of a supercell thunderstorm are intimately connected with the lowest levels. Coherent structures identified at upper levels directly influence surface vorticity evolution and cannot be neglected when investigating tornadogenesis. One plausible mechanism for the coupling between upper and lower levels is the propagation of inertial vortex waves. These oscillatory modes are known to exist on idealized vortices causing localized regions of enhanced tilting and stretching that lead to a propagation of local maxima of vorticity. We will present analysis of model results that suggest physical mechanisms for these theoretical ideas.