| Abstrakt: |
We present an experimental study simulating atmospheric dust devils in a controlled laboratory experiment. The experimental facility, called the "Barrel of Ilmenau" (www.ilmenauer-fass.de) represents a classical Rayleigh‐Bénard set‐up and is believed to model the phenomena in a convective atmospheric boundary layer fairly well. Our work complements and extends the numerical work of Giersch and Raasch (2021)https//doi.org/10.1029/2020jd034334 by experiments. Dust devils are thermal convective vortices with a vertical axis of rotation visualized by entrained soil particles. They evolve in the convective atmospheric boundary layer and are believed to substantially contribute to the aerosol transport into the atmosphere. Thus, their evolution, size, lifetime, and frequency of occurrence are of particular research interest. Extensive experimental studies have been conducted by field measurements and laboratory experiments so far. Beyond that, our study is the first attempt of Rayleigh‐Bénard convection (RBC) in air to investigate dust devil‐like vortices in a laboratory experiment. Up to now, this set‐up mimics the natural process of dust devil evolution as closest to reality. The flow measurement was carried out by particle tracking velocimetry using neutrally buoyant soap bubbles. We initially identified dust devil‐like vortices by eye from the Lagrangian velocity field, and in a later, more sophisticated analysis by a specific algorithm from the corresponding Eulerian velocity field. We analyzed their frequency of occurrence, observation time, and size. With our work, we could demonstrate that turbulent RBC is an appropriate model to mimic the natural process of the evolution of dust devils in the convective atmospheric boundary layer without artificial stimulation. Plain Language Summary: We could experimentally demonstrate that dust devil‐like vortices spontaneously arise in turbulent Rayleigh‐Bénard convection. This first‐time experimental survey simulates the evolution of dust devil‐like vortices in a laboratory experiment which mimics the convective atmospheric boundary layer quite closely and gets by without any artificial input of rotation. Dust devil‐like vortices are measured and identified using the particle tracking velocimetry technique. Within an observation period of 2 hr, 56 dust devil‐like vortices could be detected in total. Their properties coincide quite well with those structures identified in very recent direct numerical simulations (DNS) by Giersch and Raasch (2021, https//doi.org/10.1029/2020jd034334). As well, they show similarity to atmospheric dust devils. The size of our experimentally generated dust devil‐like vortices starts at about 1 dm and ranges up to about 1 m. This is larger than in DNS, but still smaller than in the atmosphere or in large eddy simulation. Key Points: Dust devil‐like vortices spontaneously evolve in turbulent Rayleigh‐Bénard convection at sufficiently high Rayleigh numbers Ra > 1010We studied their properties in a large‐scale Rayleigh‐Bénard experiment using Lagrangian particle tracking velocimetryThe vortical structures in the laboratory experiment are weaker than atmospheric dust devils, but they exhibit similar features [ABSTRACT FROM AUTHOR] |
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