Launch velocity characteristics of non-uniform sand in aeolian saltation

A numerical model for the vertical profile of aeolian mass flux was established based on the launch velocity probability distribution of saltating sand particles. The mean launch velocity (v̄0) was used as a primary variable in the simulation, from which the average saltation height and length could be further calculated. The results showed that the mean launch velocity, the average saltation height, and the average saltation length increased with increasing wind friction velocity (u∗), although the increases for the first two were not significant. On the other hand, the relative mean launch velocity (v̄0/u∗) was found to decrease with increasing wind friction velocity. Other interesting results were obtained from the simulation: both v̄0 and v̄0/u∗ decreased with an increase in the sand grain size, which agreed with a previous report claiming that the launch velocity was limited by the inertia of bed grains. Furthermore, decreasing dependence of the average saltation height and length was also found with increasing sand grain size. Overall, the sand grain size was of significance to the determination of probability distribution of the launch velocity and thus the saltation characteristics.