Phase diagrams of dune shape and orientation depending on sand availability.
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New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation.These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation.There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa.
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Affiliation: Equipe de Dynamique des Fluides Géologiques, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris Cedex 05, France.
ABSTRACT
New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation. No MeSH data available. Related in: MedlinePlus |
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Mentions: Within the parameter space {θ, N}, Fig. 4a shows that transitions in dune shape are captured fairly well by the ratio σF/σI. Finger dunes are observed when . For a given N-value and an increasing θ-value, the transition from barchan to finger dunes occurs for a σF/σI-value which slightly increases with N, from 0.46 ± 0.03 when N = 1 to 0.57 ± 0.02 when N = 3 (see black dots in Fig. 5). For the same transport ratio N but larger angles of divergence θ, the transition from a finger dune to asymmetric barchans occurs for a σF/σI-value which slightly decreases with N, from 0.73 ± 0.05 when N = 1.5 to 0.6 ± 0.01 when N = 3 (see red dots in Fig. 5). For N ≥ 3.5, no stable finger dunes are observed. The σF/σI-value is then always smaller than 0.53. The parameter σF/σI is also consistent with the finger domain extending up to 180° when N = 1. Note also that for a given N-value close to 1 and γ = 1.6, the σF/σI-value is maximum for divergence angles θ which are significantly larger than 90°. For larger N-values, this θ-value for which the σF/σI-value is maximum asymptotically tends to 90°. This is a consequence of the speed-up, the σF/σI-value is maximum for θ = 90° when γ = 0. |
View Article: PubMed Central - PubMed
Affiliation: Equipe de Dynamique des Fluides Géologiques, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75238 Paris Cedex 05, France.
No MeSH data available.