A simple analytical model was developed for prescribing the velocity fields in a dust devil, a small intense vortex phenomenon common in arid regions. The proposed model has a viscous "inner" region (boundary layer) composed of a Prandtl layer and an Ekman inflow layer and an inviscid "outer" region of cyclostrophic balance. Obser¬vations indicate that to a good approximation the outer flow is a Rankine combined vortex. Linearization of the equation of motion allows a solution for the radial and tangential velocities in the boundary layer and for the depth of the layer in terms of two parameters obtainable from observations: a(r), the inflow angle at the top of the Prandtl layer;and n(r), a modified Ekman length determined by the outer flow. The vertical velocity field is then found by application of the continuity equation. The velocity fields are found to resemble a first-order solution by Kuo for convective atmospheric vortices, and compare reasonably with the measurements of Sinclair.
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