Toward Large‐Eddy Simulations of Dust Devils of Observed Intensity: Effects of Grid Spacing, Background Wind, and Surface Heterogeneities

Abstract

Dust devils are convective vortices with a vertical axis of rotation made visible by lifted soil particles. Currently, there is great uncertainty about the extent to which dust devils contribute to the atmospheric aerosol input and thereby influence Earth's radiation budget. Past efforts to quantify the aerosol transport and study their formation, maintenance, and statistics using large‐eddy simulation (LES) have been of limited success. Therefore, some important features of dust devil‐like vortices simulated with LES still do not compare well with those of observed ones. One major difference is the simulated value of the core pressure drop, which is almost 1 order of magnitude smaller compared to the observed range of 250 to 450 Pa. However, most of the existing numerical simulations are based on highly idealized setups and coarse grid spacings. In this study, we investigate the effects of various factors on the simulated vortex strength with high‐resolution LES. For the fist time, we are able to reproduce observed core pressures by using a high spatial resolution of 2 m, a model setup with moderate background wind and a spatially heterogeneous surface heat flux. It is found that vortices mainly appear at the lines of horizontal flow convergence above the centers of the strongly heated patches, which is in contrast to some older observations in which vortices seemed to be created along the patch edges.

A Study of Daytime Convective Vortices and Turbulence in the Martian Planetary Boundary Layer Based on Half‐a‐Year of InSight Atmospheric Measurements and Large‐Eddy Simulations

“…This was also found in the high‐resolution terrestrial LES by Giersch et al. (2019): low‐wind conditions favor more long‐lasting vortices than high‐wind conditions.…”

“…A typical pressure field predicted by LES is shown in Figure 13, with localized vortex-induced pressure drops forming at the intersection of larger scale convective cells (Kanak, 2006;Michaels & Rafkin, 2004;Spiga et al, 2016;Toigo & Richardson, 2003). It should be emphasized here that the results we discuss in this study with our 25-m LES will be in need to be confirmed by future work using higher resolution LES (typically 5 m, a factor of 5 better) to better resolve the population of small-radius vortices (Giersch et al, 2019;Nishizawa et al, 2016).…”

Evolution and Features of Dust Devil‐Like Vortices in Turbulent Rayleigh‐Bénard Convection—A Numerical Study Using Direct Numerical Simulation

“…The number of vortex tracks decreases with increasing lifetime and the lifetime distribution indicates a relatively strong positive skew, which is typical for dust devil statistics derived from observations and numerical simulations (e.g., Giersch et al, 2019;R. Lorenz, 2011;R.…”

“…It is defined as the distance at which the absolute pressure drop is reduced to 50 % of the core pressure. For further details on dust devil track analysis, the reader is referred to Giersch et al (2019).…”

“…An example histogram of the lifetime frequency distribution from simulation RA1010A3 is displayed in Figure 1. By convention, the axes are logarithmically scaled with an interval or bin size ratio of about √ 2 on the x-axis (e.g., Giersch et al, 2019;R. D. Lorenz & Jackson, 2016).…”