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

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

“…Unfortunately, we could not determine the actual height of the vortex, since PDD spans the complete height of the observation area and may exceed it. A movie of the PDD migration during the observation period can be found under Kaestner et al (2023b).…”

“…Further data analysis, that is, vortex detection and analysis as well as the statistics of detected vortices, proceeded using in-house Python code. The Python code is available under Kaestner et al (2023a). More details on the experimental set-up and the measurement procedure can be found elsewhere (Loesch & du Puits, 2020.…”

“…The Python code for data evaluation, dust devil detection, and characterization is available under Kaestner et al (2023a) [Software]. A movie of the PDD migration path can be found under Kaestner et al (2023b) [Movie].…”

On the role of vortices in turbulent Rayleigh-Bénard convection

“…Out-of-plane vortices in particular, have been associated with thermal plumes detaching from top or bottom plates, and their presence in the flow is one of the main indicators of transition from so-called soft to hard turbulent convection 39,40 . Thunderstorms and dust devils are the most iconic examples of such vortices in the atmosphere 41 . Thus, although the analysis of the three velocity components of the flow provided valuable insight into the flow structure in the previous sections, additional discussion of the out-of-plane vortices ω z is represented to further analyze the dynamics of the turbulent flow in the current study.…”

Saltation‐Induced Dust Emission of Dust Devils in the Convective Boundary Layer—An LES Study on the Meter Scale

“…Dust devils are atmospheric vortices with a vertical axis of rotation that frequently occur under convective conditions when the surface is heated by insulation, causing strong superadiabatic temperature gradients near the ground. During the last 80 years, dust devils have been studied extensively with field measurements (e.g., Ives, 1947; Lorenz & Lanagan, 2014; Sinclair, 1964), laboratory experiments (e.g., Kaestner et al., 2023; Mullen & Maxworthy, 1977; Neakrase & Greeley, 2010) and, especially since the 21st century, with numerical simulations, utilizing large‐eddy simulation (LES) and direct numerical simulation (e.g., Giersch & Raasch, 2021; Kanak et al., 2000; Raasch & Franke, 2011). All these studies showed a wide range of values for the characteristics of dust devils, covering several orders of magnitude (Balme & Greeley, 2006; Murphy et al., 2016; Spiga et al., 2016).…”