From Glossary of Meteorology
Smaller-scale secondary vortices within a tornado core that orbit around a central axis.
The transition of a one-celled vortex into secondary vortices in laboratory and numerical simulations occurs at high swirl ratios. The vortices produce cycloidal swaths within tornado damage tracks and are often used to explain the gradation of wind damage caused by a tornado. Structures in the path of a suction vortex are damaged while others are spared.