Numerical experiments on the transition of tornado-like vortices by a nonhydrostatic axisymmetric model

The transition of tornado-like vortices is numerically investigated with the use of a nonhydrostatic axisymmetric model. Tornado-like vortices are generated by imposing a specified external force along the central axis of the computational domain that is rotating at a constant angular velocity. When the vortex transition from one to two-celled structure occurs, there is an overshoot of the radial inflow near the surface. The overshooting flow turns upward, directing outward to a larger radius. At the same time, downdraft penetrates to the surface at the rotating axis. The overshoot is generated by coupled effects of inward advection and inward pressure gradient force. The downdraft is caused by downward pressure gradient.