containing preexisting vertical vorticity at the surface, such as in some cases of nonsupercell tornadogenesis. Downdraft may have the following roles in near-ground mesocyclogenesis: tilts horizontal vorticity to produce vertical vorticity transports air containing vertical vorticity from mid-level to the surface enhances the near-ground vorticity convergence beneath the updraft tremendously by entering the updraft and stretching vertically See also Hook echo Supercell Thunderstorm Tornado Vertical draft References Bibliography Wind Tornadogenesis