ON THE DYNAMIC STABILITY OF CONVECTIVE ATMOSPHERIC VORTICES.
WASHINGTON UNIV SEATTLE DEPT OF ATMOSPHERIC SCIENCES
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Some characteristics of convective atmospheric vortices, with special reference to dust devils, are first discussed, and the presence of certain phenomena indicating dynamic instability is indicated. Theoretical models of steady vortex flow are then reviewed, and observational evidence for a two-cell structure with reversed axial flow in convective atmospheric vortices is presented. A vortex model of this kind suitable for atmospheric application is chosen to describe the undisturbed flow state of a convective atmospheric vortex within the layer where ambient thermal instability prevails. The linearized equations for periodic disturbances of vortex flow are then developed and known stability criteria obtainable from them are reviewed. The equations are then applied to the chosen vortex model. Solutions, obtained by numerical methods, of the dynamic stability problem thus formulated are presented and discussed. The theoretical results are compared with available visual observations of dust devils, and a discussion of possible implications of dynamic instability for dust devil formation and dissipation is given.