1 / 14

Measuring Mars sand flux seasonality and calibrating the threshold for sand mobility

Measuring Mars sand flux seasonality and calibrating the threshold for sand mobility. F. Ayoub , J-P. Avouac , C.E. Newman, M.I. Richardson, A. Lucas, S. Leprince , N.T. Bridges AGU Fall Meeting, December, 11, 2013 - fayoub@gps.caltech.edu. Nili Patera situation.

faunus
Download Presentation

Measuring Mars sand flux seasonality and calibrating the threshold for sand mobility

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measuring Mars sand flux seasonality and calibrating the threshold for sand mobility F. Ayoub, J-P. Avouac, C.E. Newman, M.I. Richardson, A. Lucas, S. Leprince, N.T. Bridges AGU Fall Meeting, December, 11, 2013 - fayoub@gps.caltech.edu

  2. NiliPatera situation

  3. NiliPatera dune field & HiRISE 5.3km Time-series of 9 HiRISE images covering one Mars year 2010 2011 2012 14.8km Tracking ripple migration 85m

  4. Measurement of ripple migration (amplitude and direction) Orthorectification, coregistration, and correlation with COSI-Corr Ripples displacement amplitude Bridges et al., 2012, Nature

  5. Estimating sand flux variability from sand ripple migration tracking 2010 2012 2011 Using the measured ripple migration, we estimate a sand flux Strong seasonal sand flux variation is observed

  6. What could this sand flux measurement tell us about the shear stress threshold ? Shear stress threshold (τt) is an important element for, e.g., simulation and prediction of sediment transport, climate and atmospheric simulations. But (τt) is hard to estimate on Mars due to the challenge in transposing previously established values (earth analog, lab experiment, theoretical, empirical) to Mars AND at scale relevant to simulation (i.e., large scale) The approach to use the flux measurement to estimate a shear stress threshold is: Which sediment shear threshold would allow sediment transport simulations to reproduce the sand flux observed?

  7. Sand flux prediction at NiliPatera from atmospheric simulation Atmospheric Circulation Model Sand transport law Wind Sand flux Time Time τt : shear threshold τt? Qpredicted Qmeasured K * K: constant Measured Predicted

  8. Sand flux prediction at NiliPatera from atmospheric simulation Atmospheric Circulation Model Sand transport law Wind Sand flux Time Time τt : shear threshold τt? MarsWRF GCM simulation (2° grid) Wind output every minute for one Mars year Final year prediction of a multi-year run

  9. Sand flux prediction at NiliPatera from atmospheric simulation Atmospheric Circulation Model Sand transport law Wind Sand flux Time Time τt : shear threshold τt? Transport law: with sand flux air density wind shear velocity Lettau & Lettau Qmeasured = Qrepton Qtotal (Qrepton)1.2 (Andreotti,2004) τtrange tested: 0.001 – 0.025 N/m2

  10. Linear regression between predicted and measured fluxes for a range of τt Qmeasured Sand flux (unitless) Only a small range of τt allows to reproduce the seasonal flux variation observed K * Qpredicted (Lettau & Lettau) Sand flux (unitless) Time Time

  11. Linear regression between predicted and measured fluxes for a range of τ 400 An ‘effective’ shear threshold is determined, that is relevant for wind at scale of few kilometers to few degrees 300 χ2of linear regression 200 τt = 0.009 ± 0.0015 N/m2 100 0.1 This ‘effective’ threshold is approximately one order of magnitude lower than fluid threshold estimated traditionally. 0.06 Probability density 0.02 0.015 0.005 0.010 Shear stress threshold τt(N/m2)

  12. Different transport laws give approximately same optimal threshold Lettau & Lettau Werner Durán et al. Sørensen Measured Lettau & Lettau Werner Sand flux (unitless) Durán Sørensen Sand flux (unitless) Time Time

  13. Different transport laws give approximately same optimal threshold 400 For all transport laws, only a small range of τ allows to reproduce the seasonal flux variation observed 300 χ2of linear regression 200 100 τt = 0.009-0.01 ± 0.0015 N/m2 0.1 0.06 Probability density 0.02 0.015 0.005 0.010 Shear stress threshold τt(N/m2)

  14. Conclusion Measurement of sand flux, and its seasonal variation at NiliPatera dune field. Continuous sand flux throughout the year, with strong variation between summer and winter solstices. Estimation of an ‘effective’ shear stress threshold relevant for simulation at scale from few km to few degrees. Next: Look at the annual variation of sand flux (on going work) Look at smaller scale simulation Estimation of specific parameters (e.g., grain size)

More Related