Dependency of particle size distribution at dust emission on friction velocity and atmospheric boundary-layer stability
<p>Particle size distribution of dust at emission (dust PSD) is an essential quantity to estimate 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, <span class="inline-for...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/12939/2020/acp-20-12939-2020.pdf |
| Summary: | <p>Particle size distribution of dust at emission (dust PSD)
is an essential quantity to estimate 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, <span class="inline-formula"><i>u</i><sub>∗</sub></span>, which is a surrogate
for surface shear stress and a 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 its justification.
In this paper, we analyse the dust PSD measured in the Japan Australian Dust
Experiment and show that dust PSD is dependent on <span class="inline-formula"><i>u</i><sub>∗</sub></span> and on
atmospheric boundary-layer (ABL) stability. By simple theoretical and
numerical analysis, we explain the two reasons for the latter dependency,
which are both related to enhanced saltation bombardment in convective turbulent
flows. First, <span class="inline-formula"><i>u</i><sub>∗</sub></span> 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 <span class="inline-formula"><i>u</i><sub>∗</sub></span>. Second, in
unstable conditions, turbulence is usually stronger, which leads to higher
saltation-bombardment intensity. This study confirms that dust PSD depends
on <span class="inline-formula"><i>u</i><sub>∗</sub></span> and, more precisely, on the probability distribution of
<span class="inline-formula"><i>u</i><sub>∗</sub></span>, which in turn is dependent on ABL stability; consequently,
dust PSD is also dependent on ABL. We also show that the dependency of dust
PSD on <span class="inline-formula"><i>u</i><sub>∗</sub></span> and ABL stability is made complicated by soil surface
conditions. In general, our analysis reinforces the basic conceptual
understanding that dust PSD depends on saltation bombardment and
inter-particle cohesion.</p> |
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| ISSN: | 1680-7316 1680-7324 |