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

Creators: Ayoub, F.; Avouac, J.-P.; Newman, C. E.; Richardson, M. I.; Lucas, A.; Leprince, S.; Bridges, N. T.

Abstract

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 T_s=0.01±0.0015 N m^(−2).

Additional Information

© 2014 Macmillan Publishers Limited. Received 29 January 2014. Accepted 28 August 2014. Published 30 September 2014. This work was supported by the Keck Institute for Space Studies, the Mars Data Analysis Programme (MDAP# 11-MDAP11-0013), the Gordon and Betty Moore foundation and the Mars Fundamental Research Programme (grant NNX11AF59G). We thank Professor Oded Aharonson for granting us access to his BAE SOCET-SET workstation. List of software used. SOCET-Set. Commercial software provided by BAE Systems (www.baesystems.com) used for the DEM generation from stereogrammetry. We followed the procedure recommended by the USGS (http://webgis.wr.usgs.gov/ pigwad/tutorials/socet-set/SocetSet4HiRISE.htm). Along with the DEM, the two orthorectified images from the stereopairs were generated, and one of them was used as the reference to register the time series to the topography. ISIS. Free, open source image processing software developed and provided by the USGS (http://isis.astrogeology.usgs.gov/). This software was used to pre-process the raw HiRISE imagery into a format that can be handled by COSI-Corr. The ISIS processing also extract the metadata of the images (telemetry, camera geometry and satellite jitter) from the NASA SPICE kernels, and store them into an ascii file that can be read by COSI-Corr. COSI-Corr. Free, not open source software provided by Caltech (http:// tectonics.caltech.edu/slip_history/spot_coseis/), and used to orthorectify, register and correlate the image time series. The output of COSI-Corr is the ripple displacement maps. The methodology used to process and generate these images is the one described in the User Guide. The HiRISE capability of COSI-Corr, developed by the authors of this study, will be a part of the next COSI-Corr release. PCAIM. Free and open source software provided by Caltech (http:// tectonics.caltech.edu/resources/pcaim/). This software was used to compute the PCA on the HiRISE time series. MarsWRF. Free and open source atmospheric simulation software (http:// planetwrf.com/), developed and provided by Ashima Research (http://ashimaresearch. com/). The GCM and mesoscale simulations of the wind regime at Nili Patera were computed using MarsWRF with the parameters that are described in Methods—GCM and mesoscale simulations.

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