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Article: Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed‐Up Effect

Gao, Xin / Narteau, Clément / Gadal, Cyril

Journal of geophysical research. 2021 May, v. 126, no. 5

2021

Abstract: We study the morphodynamics of reversing dunes on the gravel deposits of the alluvial fan of the Molcha river at the border between the Tibetan Plateau and the Taklamakan Desert. Independent sets of wind data show that this area of low sand availability ... ...

Abstract	We study the morphodynamics of reversing dunes on the gravel deposits of the alluvial fan of the Molcha river at the border between the Tibetan Plateau and the Taklamakan Desert. Independent sets of wind data show that this area of low sand availability is exposed to two prevailing winds from opposite directions and of different strengths. The predicted resultant transport direction of sand particles is westward. Nevertheless, satellite observations combined with field measurements and ground‐penetrating radar surveys reveal that isolated dunes a few meters high migrate eastward. This apparent dune migration paradox is resolved using numerical and analytical models that take into account the speed‐up effect and the continuous change in dune shape after each wind reversal. When a newly established wind hits what was before the steeper lee slope of the dune, the sand flux at the crest abruptly increases before relaxing back to a constant value as the crest migrates downwind and as the dune reaches a new steady shape. Integrated over the entire wind cycle, we find that this non‐linear behavior causes reversing dunes to migrate against the resultant transport direction. This migration reflects the difference in dune slope seen by irregular storm events blowing to the east and the westward wind of the daily cycle. Thus, we explore the impact of extreme events on dune morphodynamics and examine new aspects of the permanent feedback between dune topography and wind speed. We conclude that transient behaviors associated with crest reversals contribute to the observed diversity of dune patterns, even within the same area for dunes of different sizes.
Keywords	geophysics ; gravel ; ground-penetrating radar ; research ; rivers ; sand ; satellites ; storms ; topography ; wind speed ; China
Language	English
Dates of publication	2021-05
Publishing place	John Wiley & Sons, Ltd
Document type	Article
Note	JOURNAL ARTICLE
ISSN	2169-9003
DOI	10.1029/2020JF005913
Database	NAL-Catalogue (AGRICOLA)

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Article: Detecting Preseismic Signals in GRACE Gravity Solutions: Application to the 2011 Tohoku Mw 9.0 Earthquake

Panet, Isabelle / Narteau, Clément / Lemoine, Jean‐Michel / Bonvalot, Sylvain / Remy, Dominique

Journal of geophysical research. 2022 Aug., v. 127, no. 8

2022

Abstract: We conduct a global analysis of GRACE‐reconstructed gravity gradients from July 2004 to February 2011, to test whether the deep signals preceding the March 2011 Tohoku earthquake can be detected before the event as a specific feature originating from ... ...

Abstract	We conduct a global analysis of GRACE‐reconstructed gravity gradients from July 2004 to February 2011, to test whether the deep signals preceding the March 2011 Tohoku earthquake can be detected before the event as a specific feature originating from solid Earth. First, we improve the angular resolution of the gravity gradients using two overlapping ranges of azimuthal sensitivity to investigate short‐term signals of large amplitude aligned with the orientation of the Northwestern Pacific subduction. Then, we set‐up a method to identify consistent solid Earth signals shared by different GRACE gravity models. Robust signals in a model are selected based on their spatial overlap and relative intensity with the signals of another model, so that their sensitivity to the GRACE data processing and ocean dealiasing product can be tested. We show that the dipolar gravity gradient anomaly before the Tohoku earthquake is nearly unique in space and time in the GRACE GRGS03 solutions. A well‐resolved dipolar spatial pattern, typical of dislocations within the solid Earth and poorly sensitive to the ocean dealiasing model, is detected. In addition, the preseismic gravity gradient increase is highly consistent between the GRGS03 and CSR06 solutions, independently from their respective oceanic corrections, and can be clearly distinguished from rare anomalies of similar amplitudes all associated with the water cycle over continental areas. Our approach offers solutions for the continuous monitoring of the Pacific subduction belt to document transient slabs motions in real time from global satellite gravity fields, and their relation with shallower deformations and seismic events.
Keywords	earthquakes ; geophysics ; gravity ; hydrologic cycle ; models ; research ; satellites ; space and time ; subduction
Language	English
Dates of publication	2022-08
Publishing place	John Wiley & Sons, Ltd
Document type	Article
Note	JOURNAL ARTICLE
ISSN	2169-9313
DOI	10.1029/2022JB024542
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Depth dependent stress revealed by aftershocks.

Shebalin, Peter / Narteau, Clément

Nature communications

2017 Volume 8, Issue 1, Page(s) 1317

Abstract: Characterising the state of stress in the brittle upper-crust is essential in mechanics of faulting, industrial production processes, and operational earthquake forecasting. Nevertheless, unresolved questions concern the variation of pore-fluid with ... ...

Abstract	Characterising the state of stress in the brittle upper-crust is essential in mechanics of faulting, industrial production processes, and operational earthquake forecasting. Nevertheless, unresolved questions concern the variation of pore-fluid with depth and the absolute strength on tectonically active faults. Here we show that, along the San Andreas fault system, the time-delay before the onset of the power-law aftershock decay rate (the c-value) varies by three orders of magnitude in the first 20 km below the surface. Despite the influence of the lithostatic stress, there is no continuous change in c-value with depth. Instead, two decay phases are separated by an abrupt increase at an intermediate depth range of 2-5 km. This transitional regime is the only one observed in fluid-injection-induced seismic areas. This provides strong evidence for the role of fluid and a porosity reduction mechanism at depth of few kilometres in active fault zones. Aftershock statistics can then be used to predict changes in differential shear stress with depth until the brittle-ductile transition is reached.
Language	English
Publishing date	2017-11-06
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ISSN	2041-1723
ISSN (online)	2041-1723
DOI	10.1038/s41467-017-01446-y
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Book ; Online: The probabilistic nature of dune collisions in 2D

Jarvis, Paul A. / Narteau, Clement / Rozier, Olivier / Vriend, Nathalie M.

eISSN: 2196-632X

2022

Abstract: Dunes are bedforms of different size and shape, appearing throughout aeolian, subaqueous and extra-terrestrial environments. Collisions between dunes drive dune field evolution, and are a direct result of interacting dunes of different heights, ... ...

Abstract	Dunes are bedforms of different size and shape, appearing throughout aeolian, subaqueous and extra-terrestrial environments. Collisions between dunes drive dune field evolution, and are a direct result of interacting dunes of different heights, travelling at different speeds. We perform 2D cellular automaton simulations of collisions between dune pairs migrating in a steady flow. Modelled collisions can result in either downstream- or upstream-dominant coalescence (merging of dunes) or ejection, where dunes exchange mass before separating. For each of these three elementary types of interaction, we identify the mass exchange mechanism and the distinctive intermediate morphologies. Surprisingly, we show that the collision outcome depends probabilistically on the initial dune area ratio r and can be described by a narrow sigmoidal function centred on r = 1/2. Finally, we compare our simulations with laboratory experiments of dune collisions, finding good agreement concerning the intermediate morphology and the collision outcome. Our results can motivate further observational or experimental studies that validate our probabilistic collision predictions and fully determine the controls on the coalescence-ejection transition.
Subject code	910
Language	English
Publishing date	2022-11-01
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Local Wind Regime Induced by Giant Linear Dunes: Comparison of ERA5-Land Reanalysis with Surface Measurements

Gadal, Cyril / Delorme, Pauline / Narteau, Clément / Wiggs, Giles F. S. / Baddock, Matthew / Nield, Joanna M. / Claudin, Philippe

Boundary-Layer Meteorol. 2022 Dec., v. 185, no. 3 p.309-332

2022

Abstract: Emergence and growth of sand dunes results from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect ... ...

Abstract	Emergence and growth of sand dunes results from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect of a periodic large-scale dune pattern on atmospheric flows remains poorly constrained, due to a pressing lack of data in major sand seas. Here, we compare local measurements of surface winds to the predictions of the ERA5-Land climate reanalysis at four locations in Namibia, both within and outside the giant linear dune field of the Namib Sand Sea. In the desert plains to the north of the sand sea, observations and predictions agree well. This is also the case in the interdune areas of the sand sea during the day. During the night, however, an additional wind component aligned with the giant dune orientation is measured, in contrast to the easterly wind predicted by the ERA5-Land reanalysis. For the given dune orientation and measured wind regime, we link the observed wind deviation (over [Formula: see text]) to the daily cycle of the turbulent atmospheric boundary layer. During the night, a shallow boundary layer induces a flow confinement above the giant dunes, resulting in large flow deviations, especially for the slower easterly winds. During the day, the feedback of the giant dunes on the atmospheric flow is much weaker due to the thicker boundary layer and higher wind speeds. Finally, we propose that the confinement mechanism and the associated wind deflections induced by giant dunes could explain the development of smaller-scale secondary dunes, which elongate obliquely in the interdune areas of the primary dune pattern.
Keywords	climate ; sand ; sediment transport ; topography ; troposphere ; wind direction ; Namibia
Language	English
Dates of publication	2022-12
Size	p. 309-332.
Publishing place	Springer Netherlands
Document type	Article ; Online
ZDB-ID	1477639-X
ISSN	1573-1472 ; 0006-8314
ISSN (online)	1573-1472
ISSN	0006-8314
DOI	10.1007/s10546-022-00733-6
Database	NAL-Catalogue (AGRICOLA)

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Book ; Online: Coexistence of two dune growth mechanisms in a landscape-scale experiment

Lü, Ping / Narteau, Clément / Dong, Zhibao / Claudin, Philippe / Rodriguez, Sébastien / An, Zhishan / Gadal, Cyril / Pont, Sylvain Courrech du

2022

Abstract: In landscape-scale experiments at the edge of the Gobi desert, we show that various dune types develop simultaneously under natural wind conditions. Using 4 years of high-resolution topographic data, we demonstrate that, depending on sand availability, ... ...

Abstract	In landscape-scale experiments at the edge of the Gobi desert, we show that various dune types develop simultaneously under natural wind conditions. Using 4 years of high-resolution topographic data, we demonstrate that, depending on sand availability, the same wind regime can lead to two different dune orientations, which reflect two independent dune growth mechanisms. As periodic oblique dunes emerge from a sand bed and develop to 2 meters in height, we analyze defect dynamics that drive the non-linear phase of pattern coarsening. Starting from conical sand heaps deposited on gravels, we observe the transition from dome to barchan and asymmetric barchan shapes. We identify a minimum size for arm elongation and evaluate the contribution of wind reversals to its longitudinal alignment. These experimental field observations support existing theoretical models of dune dynamics boosting confidence in their applicability for quantitative predictions of dune evolution under various wind regimes and bed conditions.
Keywords	Physics - Geophysics ; Nonlinear Sciences - Pattern Formation and Solitons
Subject code	910
Publishing date	2022-07-15
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Local Wind Regime Induced by Giant Linear Dunes

Gadal, Cyril / Delorme, Pauline / Narteau, Clément / Wiggs, Giles F. S. / Baddock, Matthew / Nield, Joanna M. / Claudin, Philippe

Comparison of ERA5-Land Reanalysis with Surface Measurements

2022

Abstract	Emergence and growth of sand dunes results from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect of a periodic large-scale dune pattern on atmospheric flows remains poorly constrained, due to a pressing lack of data in major sand seas. Here, we compare local measurements of surface winds to the predictions of the ERA5-Land climate reanalysis at four locations in Namibia, both within and outside the giant linear dune field of the Namib Sand Sea. In the desert plains to the north of the sand sea, observations and predictions agree well. This is also the case in the interdune areas of the sand sea during the day. During the night, however, an additional wind component aligned with the giant dune orientation is measured, in contrast to the easterly wind predicted by the ERA5-Land reanalysis. For the given dune orientation and measured wind regime, we link the observed wind deviation (over 50\textdegree) to the daily cycle of the turbulent atmospheric boundary layer. During the night, a shallow boundary layer induces a flow confinement above the giant dunes, resulting in large flow deviations, especially for the slower easterly winds. During the day, the feedback of the giant dunes on the atmospheric flow is much weaker due to the thicker boundary layer and higher wind speeds. Finally, we propose that the confinement mechanism and the associated wind deflections induced by giant dunes could explain the development of smaller-scale secondary dunes, which elongate obliquely in the interdune areas of the primary dune pattern. Comment: 47 pages, 23 figures. Boundary-Layer Meteorol (2022)
Keywords	Physics - Geophysics ; Physics - Atmospheric and Oceanic Physics ; Physics - Fluid Dynamics
Subject code	551
Publishing date	2022-08-30
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article: Near-surface structure of a large linear dune and an associated crossing dune of the northern Namib Sand Sea from Ground Penetrating Radar: Implications for the history of large linear dunes on Earth and Titan

Chandler, Clayton K. / Radebaugh, Jani / McBride, John H. / Morris, Thomas H. / Narteau, Clement / Arnold, Karl / Lorenz, Ralph D. / Barnes, Jason W. / Hayes, Alex / Rodriguez, Sebastien / Rittenour, Tammy

Aeolian research. 2022 June 15,

2022

Abstract: We imaged the near-surface sedimentary structures of a large linear dune, flanking dune forms and an associated crossing linear dune never before studied in the northern Namib Sand Sea using 200-MHz Ground-Penetrating Radar (GPR). The dry, uniform sandy ... ...

Abstract	We imaged the near-surface sedimentary structures of a large linear dune, flanking dune forms and an associated crossing linear dune never before studied in the northern Namib Sand Sea using 200-MHz Ground-Penetrating Radar (GPR). The dry, uniform sandy conditions and wavelength used allowed for highly detailed observations of sedimentary structures to depths of ∼12 m across a >1 km lateral scan. Sedimentary features observed in the main linear dune include scouring and abrupt changes in strata such as trough cross stratification (TCS), onlap, downlap, truncation and avalanche-related bedding, all a result of complex sand transport conditions. Different phases of deposition have produced an opposed succession of strata on each side of the dune. These successions alternate 2-dimensional (2D), or bedform instability mode features with 3-dimensional (3D), or fingering mode features, separated by a clear process boundary. These alternating successions reflect a change in the dominant wind environment in the recent past. The changing winds may feed into the building and overall stability of this dune field and may be a model for conditions in other large linear/longitudinal dune fields. The subsurface structure of an oblique crossing linear dune demonstrates sand transport generally down the dune long axis in the direction predicted from modern, ERA-Interim model as well as paleoclimate model winds. This suggests relatively long-term stability of this intermediate-sized landform and the potential long-term coexistence of large dunes and secondary forms. These studies have implications for the extensive sand seas of Titan, where lack of large secondary forms may indicate a simple wind regime over long time periods.
Keywords	ground-penetrating radar ; models ; paleoclimatology ; research ; sand ; wavelengths ; wind
Language	English
Dates of publication	2022-0615
Publishing place	Elsevier B.V.
Document type	Article
Note	Pre-press version
ISSN	1875-9637
DOI	10.1016/j.aeolia.2022.100813
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Common dependence on stress for the statistics of granular avalanches and earthquakes.

Hatano, Takahiro / Narteau, Clément / Shebalin, Peter

Scientific reports

2015 Volume 5, Page(s) 12280

Abstract: Both earthquake size-distributions and aftershock decay rates obey power laws. Recent studies have demonstrated the sensibility of their parameters to faulting properties such as focal mechanism, rupture speed or fault complexity. The faulting style ... ...

Abstract	Both earthquake size-distributions and aftershock decay rates obey power laws. Recent studies have demonstrated the sensibility of their parameters to faulting properties such as focal mechanism, rupture speed or fault complexity. The faulting style dependence may be related to the magnitude of the differential stress, but no model so far has been able to reproduce this behaviour. Here we investigate the statistical properties of avalanches in a dissipative, bimodal particulate system under slow shear. We find that the event size-distribution obeys a power law only in the proximity of a critical volume fraction, whereas power-law aftershock decay rates are observed at all volume fractions accessible in the model. Then, we show that both the exponent of the event size-distribution and the time delay before the onset of the power-law aftershock decay rate are decreasing functions of the shear stress. These results are consistent with recent seismological observations of earthquake size-distribution and aftershock statistics.
Language	English
Publishing date	2015-07-21
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/srep12280
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Phase diagrams of dune shape and orientation depending on sand availability.

Gao, Xin / Narteau, Clément / Rozier, Olivier / Courrech du Pont, Sylvain

Scientific reports

2015 Volume 5, Page(s) 14677

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 ...

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.
Language	English
Publishing date	2015-09-30
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/srep14677
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