The hydrodynamic vortex ring model proposes that ball lightning is a toroidal (donut-shaped) vortex of hot, ionized gas that maintains its structure through angular momentum — similar to a smoke ring but made of plasma. In this model, a lightning strike creates a rapidly spinning ring of ionized air that curls inward on itself, forming a self-contained structure. The rotation traps hot gas inside the vortex, sustaining its luminosity, while the angular momentum prevents it from dissipating immediately.
The vortex ring model explains several key observations: the roughly spherical appearance (a rapidly spinning torus viewed from outside looks like a sphere), the slow, steady movement (the vortex propagates through the air like a smoke ring), and the defined boundary between the luminous region and the surrounding atmosphere. Mathematical analysis shows that plasma vortex rings could theoretically persist for seconds to minutes under the right conditions. However, the theory struggles to account for ball lightning's reported ability to pass through solid objects like walls and windows, which would disrupt the vortex structure.