Solitary Dunes under Bimodal Winds

Details Solitary Dunes under Bimodal Winds Solitary Dunes under Bimodal Winds

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....40.1509r&link_type=abstract

American Astronomical Society, DPS meeting #40, #15.09; Bulletin of the American Astronomical Society, Vol. 41, p.557

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Scientific paper

The high resolution and coverage achieved on Mars' surface have detailed lots of sand dunes of various types [1]. Many are reported as barchan or barchanoid dunes and present a diversity of shape ascribed to compound wind regimes, collisions or cementation. This diversity reminds us that aeolian structures are fairly complex. Although dunes have been extensively observed and documented, the conditions of their formation and evolution are still difficult to study because of the long time required for their development and their large length-scale.
We developed a laboratory approach using underwater experiments to study the morphology of dunes. This method has been used successfully to reproduce various types of dunes downsized to a few centimeters. Barchan dunes are formed using a unidirectional wind-equivalent regime on a pile of ceramic sand-sized grains [2]. Changing the wind regime to a more complex one reveals other structures. In the case of multiple wind directions star dunes can be observed. A bimodal wind regime, e.g. switching between two distinct directions, over an homogeneous layer of sand leads to transverse, longitudinal or complex compound sandbeds depending on the angle between these wind directions [3].
Here, we apply bimodal wind regimes to isolated patches of sand in order to observe the variation of morphology of the resulting dunes. We present the barchanoid dunes obtained for various angles of bimodal wind and show the transition to the "chestnut” dunes type. We also investigate sudden variations in wind direction over a barchan dune. Therefore, we illustrate how the (not so) simple barchan shape can be affected by a more complex wind regime and give a new insight in understanding dunes on Mars.
[1] http://www.mars-dunes.org/ .
[2] Hersen et al. PRL, 2003.
[3] Reffet et al. pldu.work 2008.

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