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Investigating the role of deposition on the size distribution of near-surface dust flux during erosion events

Abstract : Predicting the particle size distribution (PSD) of near-surface turbulent dust flux ( F wc ) is a key issue for estimating the size of atmospheric mineral dust. Existing dust emission schemes differ in their parametrization of the emitted dust ( F emi ) PSD, defining differently the surface inter-particle cohesive force and the influence of wind intensity. Moreover, these schemes have often been validated-fitted against field measurements, assuming PSD similarity between F wc and F emi . Here, we investigate numerically the main factors influencing F wc -PSD during erosion events. To this effect, we developed a 1D dust-dispersal model. After evaluating the model against published results, it is shown that F wc -PSD is influenced by both deposition and F emi -PSD. This latter one is shaped by the inter-particle cohesive bond exponent and the surface dust PSD. A time-to-space conversion of the dust flux variations reveals an increasing enrichment of F wc in small particles compared to F emi . This enrichment remains lower than a few percent of the total dust flux (in number) for fetch lower than 100 m, but it can rise to more than 10% for fetch longer than 1 km. This fetch dependence of F wc -PSD is explained by the slow deposition of particles having the lowest deposition velocities. Importantly, this difference between F wc and F emi PSDs is accentuated with wind intensity, with F emi -PSD dominated by particles with large deposition velocities, and in presence of a large-scale background dust concentration. The role played by the deposition process in shapingthe F wc -PSD should be considered when evaluating dust emission schemes against near-surface field measurements.
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Submitted on : Friday, October 22, 2021 - 10:46:32 AM
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Royston Fernandes, Sylvain Dupont, Eric Lamaud. Investigating the role of deposition on the size distribution of near-surface dust flux during erosion events. Aeolian Research, Elsevier, 2019, 37, pp.32-43. ⟨10.1016/j.aeolia.2019.02.002⟩. ⟨hal-02055226⟩

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