Latest Publication: Martian winds

Nature

Jackson, D. W. T., M. C. Bourke, and T. A. G. Smyth (2015), The dune effect on sand-transporting winds on Mars, Nature Communications, 6, Article number: 8796, doi:10.1038/ncomms9796 (open access).

There are no long-term meteorological stations that measure in situ wind patterns on Mars. As a consequence, we don’t know which way the winds blow on Mars, at least not at a scale that is important for fully understanding sediment and landform dynamics. Although global- and meso-scale atmospheric models are routinely deployed to meet regional and global -scale questions, they fail dramatically when they are used to understand the surface landforms on Mars. The omission of undertaking work at this scale has been a fundamental impediment in our understanding of sand dune dynamics on the surface of Mars.

2.A dune in Proctor Crater on Mars. This image shows the various directions of ripples on the surface of a Martian dune. This image is approximately 480 m across. Subset of NASA HiRISE image ESP_011909 Image credit: M. Bourke Data source: NASA/JPL-Caltech/University of Arizona

A dune in Proctor Crater on Mars. This image shows the various directions of ripples on the surface of a Martian dune. This image is approximately 480 m across. Subset of NASA HiRISE image ESP_011909
Image credit: M. Bourke
Data source: NASA/JPL-Caltech/University of Arizona

The interaction of wind and sediment at the micro-scale (< metre-scale) dominate the entrainment process. The effect of local moisture, surface slope, and topography all act to inhibit or enhance the capability of the wind to lift sediment and therefore change the surface.

Our work is the first to properly approach understanding geomorphological processes at the dune length scale on Mars by examining airflow at a similar scale (sub-dune size). Our work takes an innovative, detailed and new approach in order to understand near-surface winds on Mars. We deploy a state-of-the-art high resolution airflow (computational fluid dynamic, CFD) model to simulate near-surface (1m elevation) air flow conditions that are being forced by local dune topography. We use a high resolution digital terrain model of a dunefield on Mars built using High Resolution Imaging Science Experiment data. We combine these data to explore microscale bedforms on the planet’s surface at unprecedented sub-metre levels.

Microscale features such as surface sediment ripples are clearly evident at sufficient scales (0.25m) which allows us to investigate multi-year migration of bedforms. Acting as proxy wind vanes, these migration features have helped validate our CFD modelling in this study. We find that pre-existing large dune ridges (>100m high) are now acting as efficient flow deflectors that steer and accelerate local winds into distinctive patterns. This in turn dominates contemporary ripple movements noted in this study and we can now reveal patterns of ripple migration with associated steered winds according to local dune morphological characteristics.

Acknowledgment:

This work was funded in part by

  • The Irish Research Council New Foundations Program
  • The EU FP7 PCIG 13-GA-2013-618892 (“MarsDune”).

Dr Bourke, Earth and Planetary Surface Processes, Department of Geography, Trinity College, Dublin, Ireland

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