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Preprints
https://doi.org/10.5194/acp-2020-425
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-425
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 May 2020

Submitted as: research article | 18 May 2020

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This preprint is currently under review for the journal ACP.

Dependency of Particle Size Distribution at Dust Emission on Friction Velocity and Atmospheric Boundary-Layer Stability

Yaping Shao1, Jie Zhang2, Masahide Ishizuka3, Masao Mikami4, John Leys5, and Ning Huang2 Yaping Shao et al.
  • 1Institute for Geophysics and Meteorology, University of Cologne, Germany
  • 2Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, China
  • 3Faculty of Engineering and Design, Kagawa University, Japan
  • 4Office of Climate and Environmental Research Promotion, Japan Meteorological Business Support Center, Japan
  • 5Office of Environment and Heritage, New South Wales, Australia

Abstract. Particle size distribution of dust at emission (dust PSD) is an essential quantity to be estimated in dust studies. It has been recognized in earlier research that dust PSD is dependent on soil properties (e.g. whether soil is sand or clay) and friction velocity, u*, a surrogate for surface shear stress and descriptor for saltation bombardment intensity. This recognition has been challenged in some recent papers, causing a debate on whether dust PSD is invariant and the search for justification. In this paper, we analyze dust PSD measured in the Japan-Australian Dust Experiment and show that dust PSD is dependent on u* and on atmospheric boundary-layer stability. By simple theoretical and numerical analysis, we explain the three reasons for the latter dependency. First, under similar mean wind conditions, the mean of u* is larger for unstable than for stable conditions. Second, u* is stochastic and its probability distribution profoundly influences the magnitude of the mean saltation flux due to the non-linear relationship between saltation flux and u*. Third, in unstable conditions, turbulence is usually stronger, which leads to higher saltation-bombardment intensity. This study confirms that dust PSD depends on u*, and more precisely, on the probability distribution of u*, which itself is stability dependent. We restate that for a given soil, finer dust is released in case of stronger saltation.

Yaping Shao et al.

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Yaping Shao et al.

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Short summary
It has been recognized in earlier research that Particle size distribution of dust at emission (dust PSD) is dependent on friction velocity. This recognition has been challenged in some recent papers. Based on the analysis of experimental data, we confirm that dust PSD is dependent on friction velocity and atmospheric boundary-layer stability. By theoretical and numerical analysis, we reveal the reasons for this dependency.
It has been recognized in earlier research that Particle size distribution of dust at emission...
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