Spatiotemporal Structure of Aeolian Particle Transport on Flat Surface

We conduct numerical simulations based on a model of blowing snow to reveal the long-term properties and equilibrium state of aeolian particle transport from ${10}^{-5}\mathrm{m}$ to $10\mathrm{m}$ above the flat surface. The numerical results are as follows. (i) Time-series data of particle transport are divided into development, relaxation, and equilibrium phases, which are formed by rapid wind response below $10 \hspace{0.5 ex} $\mathrm{c}\mathrm{m}$$andgradualwindresponseabove$10 \hspace{0.5 ex} $\mathrm{c}\mathrm{m}$$. (ii) The particle transport rate at equilibrium is expressed as a power function of friction velocity, and the index of 2.35 implies that most particles are transported by saltation. (iii) The friction velocity below $100\mu \mathrm{m}$ remains roughly constant and lower than the fluid threshold at equilibrium. (iv) The mean particle speed above $300 \hspace{0.5 ex} \mu$\mathrm{m}$$islessthanthewindspeed,whereasthatbelow$300 \hspace{0.5 ex} \mu$\mathrm{m}$$ exceeds the wind speed because of descending particles. (v) The particle diameter increases with height in the saltation layer, and the relationship is expressed as a power function. Through comparisons with the previously reported random-flight model, we find a crucial problem that empirical splash functions cannot reproduce particle dynamics at a relatively high wind speed.