Limits...
Phase diagrams of dune shape and orientation depending on sand availability.

Gao X, Narteau C, Rozier O, Courrech du Pont S - Sci Rep (2015)

Bottom Line: 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.

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.

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

Dune field orientation with respect to the angle θ between the two winds for different transport ratio N and two conditions of sand availability.red N = 1, blue N = 1.5, green N = 2, black N = 5. (a) Dunes grow in height and wavelength from a flat bed with no restriction in sand availability; (b) Dunes extend or propagate on a non-erodible ground from a localized sand source. All orientations are defined with respect to the dominant wind direction using 2D spatial autocorrelation. Symbols differentiate finger dunes (circles), trains of barchan dunes (triangles) and coexistence of barchans and finger dunes (squares). For linear dunes, symbols also differentiate between transverse (full circles), oblique (double circles) and longitudinal dunes (open circles). Solid lines show the predicted dune orientation derived from equations (1) and (2) using γ = 1.6, the best-fit flux-up ratio. Error bars show the standard deviation for 10 realizations with different diffusion rates to evaluate the role of defects (see Supplementary Note 4). Note the good agreement between the prediction of the numerical model and the analytical solutions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4588573&req=5

f3: Dune field orientation with respect to the angle θ between the two winds for different transport ratio N and two conditions of sand availability.red N = 1, blue N = 1.5, green N = 2, black N = 5. (a) Dunes grow in height and wavelength from a flat bed with no restriction in sand availability; (b) Dunes extend or propagate on a non-erodible ground from a localized sand source. All orientations are defined with respect to the dominant wind direction using 2D spatial autocorrelation. Symbols differentiate finger dunes (circles), trains of barchan dunes (triangles) and coexistence of barchans and finger dunes (squares). For linear dunes, symbols also differentiate between transverse (full circles), oblique (double circles) and longitudinal dunes (open circles). Solid lines show the predicted dune orientation derived from equations (1) and (2) using γ = 1.6, the best-fit flux-up ratio. Error bars show the standard deviation for 10 realizations with different diffusion rates to evaluate the role of defects (see Supplementary Note 4). Note the good agreement between the prediction of the numerical model and the analytical solutions.

Mentions: Using the numerical model output, we now turn to quantitative estimates of dune trends and sediment transport properties in the parameter space {θ, N} of bidirectional wind regimes. Symbols in Fig. 3a show the dune orientation αI in the bed instability mode when dunes grow in height from the underlying sediment layer. For the same {θ, N} -values, symbols in Fig. 3b show the dune trend αF in the fingering mode when dunes grow by extension away from a localized sand source. These two dune trends αI and αF measured in the numerical experiments compare well to the solutions of the theoretical model proposed by Courrech du Pont et al.10.


Phase diagrams of dune shape and orientation depending on sand availability.

Gao X, Narteau C, Rozier O, Courrech du Pont S - Sci Rep (2015)

Dune field orientation with respect to the angle θ between the two winds for different transport ratio N and two conditions of sand availability.red N = 1, blue N = 1.5, green N = 2, black N = 5. (a) Dunes grow in height and wavelength from a flat bed with no restriction in sand availability; (b) Dunes extend or propagate on a non-erodible ground from a localized sand source. All orientations are defined with respect to the dominant wind direction using 2D spatial autocorrelation. Symbols differentiate finger dunes (circles), trains of barchan dunes (triangles) and coexistence of barchans and finger dunes (squares). For linear dunes, symbols also differentiate between transverse (full circles), oblique (double circles) and longitudinal dunes (open circles). Solid lines show the predicted dune orientation derived from equations (1) and (2) using γ = 1.6, the best-fit flux-up ratio. Error bars show the standard deviation for 10 realizations with different diffusion rates to evaluate the role of defects (see Supplementary Note 4). Note the good agreement between the prediction of the numerical model and the analytical solutions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588573&req=5

f3: Dune field orientation with respect to the angle θ between the two winds for different transport ratio N and two conditions of sand availability.red N = 1, blue N = 1.5, green N = 2, black N = 5. (a) Dunes grow in height and wavelength from a flat bed with no restriction in sand availability; (b) Dunes extend or propagate on a non-erodible ground from a localized sand source. All orientations are defined with respect to the dominant wind direction using 2D spatial autocorrelation. Symbols differentiate finger dunes (circles), trains of barchan dunes (triangles) and coexistence of barchans and finger dunes (squares). For linear dunes, symbols also differentiate between transverse (full circles), oblique (double circles) and longitudinal dunes (open circles). Solid lines show the predicted dune orientation derived from equations (1) and (2) using γ = 1.6, the best-fit flux-up ratio. Error bars show the standard deviation for 10 realizations with different diffusion rates to evaluate the role of defects (see Supplementary Note 4). Note the good agreement between the prediction of the numerical model and the analytical solutions.
Mentions: Using the numerical model output, we now turn to quantitative estimates of dune trends and sediment transport properties in the parameter space {θ, N} of bidirectional wind regimes. Symbols in Fig. 3a show the dune orientation αI in the bed instability mode when dunes grow in height from the underlying sediment layer. For the same {θ, N} -values, symbols in Fig. 3b show the dune trend αF in the fingering mode when dunes grow by extension away from a localized sand source. These two dune trends αI and αF measured in the numerical experiments compare well to the solutions of the theoretical model proposed by Courrech du Pont et al.10.

Bottom Line: 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.

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.

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