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Nat Commun. 2014 Sep 30;5:5096. doi: 10.1038/ncomms6096.

Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux.

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Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, MC 100-23, Pasadena, California 91125, USA.
Ashima Research, 600 South Lake Avenue, Suite 104, Pasadena, California 91106, USA.
Space Department, 200-W230, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA.


Coupling between surface winds and saltation is a fundamental factor governing geological activity and climate on Mars. Saltation of sand is crucial for both erosion of the surface and dust lifting into the atmosphere. Wind tunnel experiments along with measurements from surface meteorology stations and modelling of wind speeds suggest that winds should only rarely move sand on Mars. However, evidence for currently active dune migration has recently accumulated. Crucially, the frequency of sand-moving events and the implied threshold wind stresses for saltation have remained unknown. Here we present detailed measurements of Nili Patera dune field based on High Resolution Imaging Science Experiment images, demonstrating that sand motion occurs daily throughout much of the year and that the resulting sand flux is strongly seasonal. Analysis of the seasonal sand flux variation suggests an effective threshold for sand motion for application to large-scale model wind fields (1-100 km scale) of τ(s)=0.01±0.0015 N m(-2).


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