Minimal size of a barchan dune

Abstract

Barchans are dunes of high mobility which have a crescent shape and propagate under conditions of unidirectional wind. However, sand dunes only appear above a critical size, which scales with the saturation distance of the sand flux [P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002); B. Andreotti, P. Claudin, and S. Douady, Eur. Phys. J. B 28, 321 (2002); G. Sauermann, K. Kroy, and H. J. Herrmann, Phys. Rev. E 64, 31305 (2001)]. It has been suggested by P. Hersen, S. Douady, and B. Andreotti, Phys. Rev. Lett. 89, 264301 (2002) that this flux fetch distance is itself constant. Indeed, this could not explain the proto size of barchan dunes, which often occur in coastal areas of high litoral drift, and the scale of dunes on Mars. In the present work, we show from three dimensional calculations of sand transport that the size and the shape of the minimal barchan dune depend on the wind friction speed and the sand flux on the area between dunes in a field. Our results explain the common appearance of barchans a few tens of centimeter high which are observed along coasts. Furthermore, we find that the rate at which grains enter saltation on Mars is one order of magnitude higher than on Earth, and is relevant to correctly obtain the minimal dune size on Mars.

Dune formation on the present Mars

“…As shown in a previous work, the minimal dune width W min is around 13ℓ s , and is approximately independent of the interdune flux, q in /q s [45]. In this manner, W min yields, through eq.…”

Aeolian Sand Transport in Out‐of‐Equilibrium Regimes

“…Indeed, it is admitted [Claudin and Andreotti , 2006;Parteli et al, 2007] that the saturation length actually controls the initial size of sand dunes emerging from a flat sand bed. In the picture where the saturation length is governed by the drag length [Andreotti et al, 2010] that is independent of the wind speed, the minimal size of a dune is therefore invariant with the wind strength.…”

Vegetation and Induration as Sand Dunes Stabilizators

“…While the saturation length ℓ s on Earth is around 50 cmwhich is calculated from eq. (3) with u * ≈ 0.37 m/s obtained from measurements and calculations of wind friction speed in northeastern Brazil (Jimenez et al 1999;Sauermann et al 2003;Parteli et al 2006) -we have obtained ℓ s ≈ 17 m for Mars using the parameters mentioned above, with which we reproduced the Arkhangelsky dunes. The minimal dune width obtained from simulations is around 10 times ℓ s , both using parameters for Mars and for Earth .…”