Which length scale dominates saturation of aeolian sand transport?

The saturation length of aeolian sand transport (Ls), characterizing the distance needed by wind-blown sand to adapt to changes in the wind shear, is essential for accu-rate modeling of the morphodynamics of Earth’s sandy land-scapes and, in particular, for explaining the formation and shape of sand dunes. In the last decade, it has become a widely-accepted hypothesis that Ls is proportional to the characteristic distance needed by transported particles to reach the wind speed (the “drag length”). Here we chal-lenge this hypothesis. From extensive numerical Discrete Element Model simulations, we find that, for medium and strong winds, Ls ∝ V 2 s /g, where Vs is the saturated value of the average speed of sand particles traveling above the surface and g the gravitational constant. We show that this proportionality is consistent with a recent analytical model, in which the drag length is just one of four similarly impor-tant length scales relevant for sand transport saturation. 1