Evolution and Features of Dust Devil-Like Vortices in Turbulent Rayleigh-Bénard Convection - An Experimental Study

Abstract

Dust devils are micro-beta scale (20-200 m in horizontal scale;Stull, 1988), convective vortex structures with vertical rotational axis appearing at ground level of the atmosphere. They are detected in terrestrial and Martian atmospheres (Balme & Greeley, 2006). Dust devils occur, when hot air near a solar heated surface hotspot rises quickly through the cooler air layer above. The thermal convective phenomenon is initiated by "superadiabatic lapse rate" (Balme & Greeley, 2006) at the irradiated surface and continues as plume outside the thermal boundary layer (Sinclair, 1969). Under certain conditions, for example, local vortices initiated by convection or deflected wind at obstacles, the up-drafting air starts to rotate (Balme & Greeley, 2006;Carroll & Ryan, 1970;Renno et al., 2004). Due to vertical stretching of the uprising column of hot air, entrained dust moves toward the axis of rotation. Thus, conservation of angular momentum leads to increased tangential velocity at smaller radii, and hence, an enhancement of the spinning effect. A secondary flow induced by the pressure drop further sucks hot air horizontally from the surface inward to the bottom of the initial vortex structure (Metzger, 1999). Thus, the spinning effect continuously intensifies as more hot air rushes and raises and the vortex becomes