Measured and predicted aeolian flux at Nili Patera, Mars: Computational Fluid Dynamics-derived transport modelling and Cosi-CORR rates

Until recently, sand dunes on Mars were thought to be relict landforms from paleo-atmospheric conditions. However, recent evidence from high resolution imagery of Mars’ surface have shown that aeolian processes are a dominant, contemporary force, driving geomorphological change in dune fields across the planet. Images from the HiRISE camera have demonstrated that not only are dune fields active on Mars, but they are undergoing change comparable to some terrestrial rates.

In the absence of localised in situ wind data returned by successive lander missions, the atmospheric-surface interactions contributing to aeolian change across the surface of Mars have largely relied on mesoscale modelling, these large-scale models have not fully resolved the processes occurring at local landform scales. In order to attempt to resolve the interactions driving the modification of dune fields, microscale wind flow modelling (<2 m grid spacing) is required over a site which has been shown to undergo change over the history of HiRISE imagery.

A large barchan dune field in the Nili Patera caldera was selected for examination, as this site undergoes significant aeolian change. This site has a robust HiRISE image collection, but no in situ data, and is therefore an ideal location to test a new multiscale airflow modelling approach. This study proposes combining macro- (>100 km), meso- (>2 km) and microscale (>2 m) modelling of the Martian atmosphere.

The resolution of a Global Climate Model (GCM) is too coarse to resolve the near-surface processes themselves, but their output can be used to provide an initial state and boundary conditions for mesoscale modelling. However, the maximum resolution of a typical mesoscale model is still too coarse to resolve the microscale dynamics contributing to aeolian change at dune fields on Mars. To examine the fine-scale interactions occurring over the surface of dune fields, microscale Computational Fluid Dynamics (CFD) simulations utilising the mesoscale model output are required.

The surface shear stress output from the CFD simulations and corresponding flux predictions were directly compared to HiRISE observations of Nili Patera, using COSI-Corr software to verify the microscale modelling results. We find that this multi-scale modelling approach provides promising initial comparisons between CFD simulations and HiRISE observations, both in the directionality of dune change and the rates of sediment flux, and different Mars seasons., however these observations are influenced by the seasonal variability on Mars, altering approach directions and wind speeds to produce heterogeneous patterns of aeolian flux.