Abstract
A two-way interactive, nested-grid simulation of a rotating supercell thunderstorm was performed. After 90 min the genesis of a descending incipient tornado vortex initially located aloft was simulated. The associated pressure-deficit tube subsequently built downward into the subcloud layer, where it continually fed upon a low-level source of vertical vorticity possibly introduced by the low-level downdraft. The pressure-deficit tube then drew in the low-level vorticity-rich air, allowing it to descend to the surface. A strong vortex thus formed in the subcloud field.
