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Data from: Gentle topography increases vertical transport of coarse dust by orders of magnitude

Citation

Heisel, Michael; Chen, Bicheng; Kok, Jasper; Chamecki, Marcelo (2021), Data from: Gentle topography increases vertical transport of coarse dust by orders of magnitude, Dryad, Dataset, https://doi.org/10.5068/D15Q4C

Abstract

The presence of coarse mineral dust in the atmosphere has been substantiated in several recent measurement campaigns, which include observations of particles up to and above 100 micrometer in diameter. Yet, atmospheric dust models either do not include particles larger than 20 micrometer or severely underestimate their concentrations. One possibility for the underestimated concentrations is that models do not represent enhancements of particle transport due to subgrid-scale topography. Here, large-eddy simulations are used in combination with Lagrangian particle tracking to assess the impact of gentle two-dimensional topography with 50 and 100 m elevation on the vertical transport of coarse dust in neutrally-stratified conditions. The presence of topography significantly increases the likelihood that 5 and 20 micrometer particles reach several hundred meters in altitude. Further, topography increases this likelihood by orders of magnitude for larger 60 micrometer particles. Three mechanisms are observed to contribute to the increased vertical transport: a strong upward mean flow region on the uphill side of the topography, ejection of particles downwind of the topography crest, and enhanced vertical dispersion in the wake of the crest. The compounding effects of these mechanisms provide a pathway for coarse dust emitted from the surface to reach elevations where they can be further transported into the free atmosphere by large-scale motions such as convective plumes. While these findings are motivated by mineral dust observations, they are generally applicable to other heavy aerosols such as pollen.

Methods

The dataset is a collection of computational results based on large-eddy simulation (LES) of the atmospheric boundary layer and Lagrangian tracking of coarse dust particles. Three simulations of the boundary layer are included: over flat terrain, over a small 50 m hill, and over a large 100 m hill. The LES was wall-modeled, and the two-dimensional hill was represented using immersed boundary methods.

Coarse dust particles were released near the ground in the simulations and their trajectories were tracked based on the LES velocity fields. Three particle sizes - 5, 20, and 60 micrometer diameter - were released for each of the three LES topography cases, thus totaling nine scenarios. Further details regarding the methodology are available in the related article.

Usage Notes

The data comprise processed statistics corresponding to the published results of the simulations. These include time-averages LES velocities and particle trajectory statistics. The data are organized as tab-separated values in text files, where the header rows provide relevant information. The figure number in each file name refers to the corresponding figure in the related article.

Funding

Cold Regions Research and Engineering Laboratory, Award: W913E520C0001

Army Research Laboratory, Award: W911NF2020150