Vortex sheet roll-ups are only sustainable when flow into, or out of, the vorticity axis of the roll-up is restricted. In the case of a supercell environment, vertically oriented roll-ups are generated along vertically oriented vortex sheets formed by surface deformation processes, such as those along the rear-flank, or forward-flank, gust fronts. Unrestricted roll-up processes of this type are commonly referred to as gustnadoes, and do not directly lead to tornadogenesis. However, when occurring under the mesocyclone of a supercell storm, downward acceleration of vertical flow drawn into the roll-ups from above is shown to be restricted by the vertical dynamic pressure gradient produced by the mesocyclone aloft. This allows roll-ups to develop to tornado intensities.
Our numerical study suggests that the roll-up of a vortex sheet along a supercell's rear-flank gust front is an important dynamical process leading to surface tornadogenesis and vortex intensification aloft. This presentation will discuss the dynamics of the roll-up process in more detail and draw comparisons with existing vortex line analyses of pre-tornadogenesis environments.