Spatiotemporal Structure of Aeolian Particle Transport on Flat Surface

TL;DR

This study uses numerical simulations to analyze the long-term behavior and structure of aeolian particle transport over flat surfaces, revealing phases, scaling laws, and particle dynamics relevant to saltation processes.

Contribution

It introduces a detailed numerical model of blowing snow to elucidate the spatiotemporal structure and equilibrium properties of aeolian transport, highlighting the limitations of empirical splash functions at high wind speeds.

Findings

Transport rate follows a power law with friction velocity, indicating saltation dominance.

Friction velocity below 100 μm remains below fluid threshold at equilibrium.

Particle size increases with height, following a power law.

Abstract

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 $10^{-5} \hspace{0.5 ex} \mathrm{m}$ to $10 \hspace{0.5 ex} \mathrm{m}$ 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 $10 \hspace{0.5 ex} \mathrm{cm}$ and gradual wind response above $10 \hspace{0.5 ex} \mathrm{cm}$. (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 $100 \hspace{0.5 ex} \mu\mathrm{m}$ remains roughly constant and lower than the fluid threshold at equilibrium. (iv) The mean particle speed above $300 \hspace{0.5 ex} \mu\mathrm{m}$ is less than the wind speed, whereas that below $300 \hspace{0.5 ex} \mu\mathrm{m}$ 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.