SOME ASPECTS OF THE DYNAMICS OF TORNADOES

Abstract

In this paper an attempt is made to construct a dynamical model for a tornado that may explain some of its known features. The assumption is made that a tornado is dynamically equivalent to a combination of a pure sink and a pure vortex in the hydrodynamic sense. The compressibility of the air is taken into account, but the air is assumed to be dry. Friction is neglected and the motion induced by the disturbance is assumed to be horizontal. It is found that, because of the compressibility of the air, the flow is separated into three main regions, an outer region in which the flow is subsonic, an innermost region which cannot belong to the outer flow, and a middle region that separates the two, in which the flow is supersonic. Formulas are derived by which the radii of these regions may be computed. The minimum possible pressure and the maximum possible speed are computed. The vertical shape of the funnel is also computed on the assumption that it is parallel to the surface of the critical flow.