Soil Moisture Effects on Sand Saltation and Dust Emission Observed over the Horqin Sandy Land Area in China

In this study, the effects of soil moisture on sand saltation and dust emission over the Horqin Sandy Land area are investigated, based on observations of three dust events in 2010. The minimum friction velocity initiating the motion of surface particles, namely, the threshold friction velocity, is estimated to be 0.34, 0.40, and 0.50 m s-1 under the very dry, dry, and wet soil conditions, respectively. In comparison withthe observations during the dust events under the very dry and dry soil conditions, the dust emission flux during the wet event is smaller, but the saltation activities of sand particles (d 50m) are stronger. The size distributions of airborne dust particles (0.1 d 20 m) show that concentrations of the finer dust particles (0.1 d 0.3 m) have a secondary peak under dry soil conditions, while they are absent under wet soil conditions. This suggests that the surface soil particle size distribution can be changed by soil moisture. Under wet soil conditions, the particles appear to have a larger size, and hence more potential saltating particles are available. This explains the occurrence of stronger saltation processes observed under wet soil conditions.