Inferring wind speed from ripple and dune migration on Mars

Dunes and ripples are markers of eolian activity. Dunes arise and evolve from the action of wind blowing on sand grains and can thus provide information on past and current wind regime. They constantly adjust and adapt their shape through feedback between the bed topography and the near-surface air flow. This interaction modulates erosion of the stoss side and deposition on the lee side, and eventually results in the dune migration. Here, we present a workflow that quantitatively relates the rate of barchan dunes migration, which can be measured from remote sensing, to the wind velocity, either measured at a meteorological station or extracted from reanalysis data. We validate this workflow using data from Earth and apply it on Mars. 

The workflow requires the selection of a sand transport law and the use of computational fluid dynamic (CFD) modeling. This modeling is used to estimate the effect of the local topography on the near surface airflow, namely the speed-up effect. We compare the dune migration rate predicted through the workflow to remote sensing observations, at two barchan dune fields located along the southern rim of the Arabia Gulf. After validating this workflow on Earth, we apply it to a barchan dune field on Mars. The dune migration is used to derive a wind speed distribution, averaged over one Martian year. Finally, we use ripple migration, that is much faster than dune migration, to derive the sub-annual variation of the wind speed.