The shape of barchan dunes

Kroy, Klaus; Fischer, Sebastian; Obermayer, Benedikt

doi:10.1088/0953-8984/17/14/012

Cited by 40 publications

(41 citation statements)

References 24 publications

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“…In their experiment, they found dunes 800 times smaller than the aeolian dunes, since ρ fluid of water is 10 3 kg/m 3 . As observed recently, there are other physical variables besides ℓ drag which appear relevant to explain the scale of dunes [15]. Barchans are also found on Mars, where the atmospheric density is 100 times smaller than on earth.…”

Section: Introductionmentioning

confidence: 60%

“…7a how different a barchan dune of width 180 m appears with different values of shear velocity and sand influx q in /q s from 1 to 50%. Kroy et al (2005) [15] have already shown that the aspect ratio H/L increases with u * . Furthermore, there is an interesting feature which we can only see with three-dimensional calculations.…”

Section: Resultsmentioning

confidence: 88%

“…3). On the basis of this surprising inconsistence, it has been suggested that still unknown microscopic properties of the martian saltation must be understood and taken into account in order to correctly predict the size of dunes on Mars [15].…”

Section: Introductionmentioning

confidence: 99%

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Minimal size of a barchan dune

2007

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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.

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Section: Introductionmentioning

confidence: 60%

Section: Resultsmentioning

confidence: 88%

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Minimal size of a barchan dune

2007

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“…However, because of the low fluid density on Mars, saltation there takes a much greater distance to reach steady state than on Earth. In fact, the "drag length" required to accelerate particles to the fluid speed is approximately two orders of magnitude greater on Mars than on Earth [Kroy et al, 2005]. Since wind tunnels require ∼10 meters to reach steady-state saltation for Earth conditions [Shao and Raupach, 1992], studies using similar wind tunnels for Mars conditions cannot measure steady-state conditions, and will thus underestimate the mass flux [Anderson and Haff, 1991;Shao and Raupach, 1992].…”

Section: Discussionmentioning

confidence: 99%

An improved parameterization of wind‐blown sand flux on Mars that includes the effect of hysteresis

Kok

2010

Geophysical Research Letters

115

210

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[1] Saltation, the wind-driven hopping motion of sand grains, forms dunes and ripples, and ejects fine dust particles into the atmosphere on Mars. Although the wind speed at which saltation is initiated, the "fluid threshold," has been studied extensively, the wind speed at which saltation is halted, the "impact threshold," has been poorly quantified for Mars conditions. I present an analytical model of the impact threshold, which is in agreement with measurements and numerical simulations for Earth conditions. For Mars conditions, the impact threshold is approximately an order of magnitude below the fluid threshold, in agreement with previous studies. Saltation on Mars can thus be sustained at wind speeds an order of magnitude less than required to initiate it, leading to the occurrence of hysteresis. I include the effect of hysteresis into an improved parameterization of sand transport on Mars.

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“…The Martian higher entrainment rate, which is a result of the larger splash events on Mars, shortens the length of flux saturation and reduces the scale of dunes that is obtained if only the Martian larger saltation length is considered [48,53];…”

Section: Discussionmentioning

confidence: 99%

Dune formation on the present Mars

Parteli

Herrmann

2007

Phys. Rev. E

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We apply a model for sand dunes to calculate formation of dunes on Mars under the present Martian atmospheric conditions. We find that different dune shapes as those imaged by Mars Global Surveyor could have been formed by the action of sand-moving winds occuring on today's Mars. Our calculations show, however, that Martian dunes could be only formed due to the higher efficiency of Martian winds in carrying grains into saltation. The model equations are solved to study saltation transport under different atmospheric conditions valid for Mars. We obtain an estimate for the wind speed and migration velocity of barchan dunes at different places on Mars. From comparison with the shape of bimodal sand dunes, we find an estimate for the timescale of the changes in Martian wind regimes.

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The shape of barchan dunes

Cited by 40 publications

References 24 publications

Minimal size of a barchan dune

Minimal size of a barchan dune

An improved parameterization of wind‐blown sand flux on Mars that includes the effect of hysteresis

Dune formation on the present Mars

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