Comment on "Minimal size of a barchan dune"

Abstract

It is now an accepted fact that the size at which dunes form from a flat sand bed as well as their `minimal size' scales on the flux saturation length. This length is by definition the relaxation length of the slowest mode toward equilibrium transport. The model presented by Parteli, Duran and Herrmann [Phys. Rev. E 75, 011301 (2007)] predicts that the saturation length decreases to zero as the inverse of the wind shear stress far from the threshold. We first show that their model is not self-consistent: even under large wind, the relaxation rate is limited by grain inertia and thus can not decrease to zero. A key argument presented by these authors comes from the discussion of the typical dune wavelength on Mars (650 m) on the basis of which they refute the scaling of the dune size with the drag length evidenced by Claudin and Andreotti [Earth Pla. Sci. Lett. 252, 30 (2006)]. They instead propose that Martian dunes, composed of large grains (500 micrometers), were formed in the past under very strong winds. We show that this saltating grain size, estimated from thermal diffusion measurements, is not reliable. Moreover, the microscopic photographs taken by the rovers on Martian aeolian bedforms show a grain size of 87 plus or minus 25 micrometers together with hematite spherules at millimetre scale. As those so-called ``blueberries'' can not be entrained by reasonable winds, we conclude that the saltating grains on Mars are the small ones, which gives a second strong argument against the model of Parteli et al.

A six page comment on ``Minimal size of a barchan dune'' by Parteli, Duran and Herrmann [Phys. Rev. E 75, 011301 (2007) arXiv:0705.1778]

References in corpus (6)

• A Continuum Saltation Model for Sand Dunes
• A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples
• Minimal model for aeolian sand dunes
• Corridors of barchan dunes: stability and size selection
• Selection of dune shapes and velocities. Part 2: A two-dimensional modelling
• Minimal size of a barchan dune

Cited by in corpus (5)

• The physics of wind-blown sand and dust
• A two-species continuum model for aeolian sand transport
• Reply to "Comment on `Minimal size of a barchan dune' "
• Measurements of the aeolian sand transport saturation length
• Bedforms in a turbulent stream.Part 2: Formation of ripples by primary linear instability and of dunes by non-linear pattern coarsening