An observational and idealized numerical examination of low-level counter-rotating vortices in the rear flank of supercells

Observations are reviewed that show that the dominant kinematic elements of the supercell rear flank are a downdraft trailing an adjacent updraft, a gust front, and counter-rotating vortices embedded in the gust front convergence zone. The associated vortex lines are shaped like arches. In an idealized simulation of the evolution of this flow structure, vortex rings are observed to form around a cool downdraft and in the adjacent periphery of the updraft. These rings are lofted in the rear portion of the updraft, and depressed in the downdraft. This resulting kinematic pattern strongly resembles the observations. Such a baroclinicallyforced process is plausible in actual supercells, although it is uncertain whether it is ever sufficient for tornado formation, and to what extent the tilting of low-level quasi-streamwise vorticity plays a role. ––––––––––––––––––––––––