Vortex breakdown

From Glossary of Meteorology

vortex breakdown

The region of a vortex between a supercritical upstream flow incapable of supporting upstream-propagating centrifugal waves and a subcritical flow that allows downstream- propagating centrifugal waves.

The region is usually marked by abrupt swelling and often turbulence and reverse axial flow in the downstream side. Vortex breakdown is sometimes observed in tornadoes.
See hydraulic jump.