A Simple Analytical Model for the Dust Devil
CALIFORNIA UNIV BERKELEY LAWRENCE RADIATION LAB
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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 propose model has a viscous inner region boundary layer composed of a Prandtl layer and an Ekman inflow layer and an inviscid outer1 region of cyclostrophic balance. Observations 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 the parameters obtainable from observations alphar, the inflow angle at the top of the Prandtl layer and etar, 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.