TY - JOUR

T1 - Toward Large-Eddy Simulations of Dust Devils of Observed Intensity: Effects of Grid Spacing, Background Wind, and Surface Heterogeneities

AU - Giersch, S.

AU - Brast, M.

AU - Hoffmann, F.

AU - Raasch, S.

N1 - Funding information: This work was funded by the German Research Foundation (DFG) under Grant RA 617/31-1. All simulations were performed on the Cray XC40 and Atos system of the North-German Supercomputing Alliance (HLRN-3/4) located in Berlin and Göttingen. The LES model PALM is freely available (revision 3094, http://palm.muk.uni-hannover.de/trac/browser/?rev=3094). The output, which was used to generate figures and tables, is accessible via the https://doi.org/10.25835/0095133 website. Also, the user-specific code for detecting dust devils, model steering files, and scripts for postprocessing the raw data is stored there.

PY - 2019/8/15

Y1 - 2019/8/15

N2 - 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.

AB - 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.

KW - convective boundary layer

KW - dust devils

KW - large-eddy simulation

KW - PALM

UR - http://www.scopus.com/inward/record.url?scp=85070186092&partnerID=8YFLogxK

U2 - 10.1029/2019JD030513

DO - 10.1029/2019JD030513

M3 - Article

AN - SCOPUS:85070186092

VL - 124

SP - 7697

EP - 7718

JO - Journal of Geophysical Research: Atmospheres

JF - Journal of Geophysical Research: Atmospheres

SN - 2169-897X

IS - 14

ER -