Laboratory and Atmospheric Vortex Instabilities

Mesoscale atmospheric vortices such as dust devils, tornadoes and fire whirls may be modelled in the laboratory if the similarity requirement of equal advance angles of the upward swirling flow is preserved. Theoretical analysis shows that linear vortices are stable even for large pertubations near their base. However, they become unstable to small downstream perturbations which change the relative advance angle to about 68 . Laboratory experiments which have preserved similarity to large ambient vortices have demonstrated destructive instability. They suggest that flow pertubations introduced by appropriate cloud seeding could destroy tornadoes.