Inferring Airflow Across Martian Dunes From Ripple Patterns and Dynamics

Creators: Hood, D. R.; Ewing, R. C.; Roback, K. P.; Runyon, K.; Avouac, J.-P.; McEnroe, M.

Abstract

Large ripples form striking patterns on the slopes of martian sand dunes which can be mapped and tracked using high-resolution optical images. The ripples vary in orientation, wavelength, plan-view morphology, and rates of migration. The variations in the ripple patterns are recognized to signal the effects of the regional and local winds and feedbacks between winds and dune topography. We examine the ripple patterns and the motion of these ripples to interpret airflow dynamics around dunes in the dune field at Nili Patera. We find that coincident changes in ripple patterns and migration rates in dune wakes indicate reattachment lengths of 4–7 brink heights. This reattachment length is similar to length scales of flow reattachment for airflow over dunes measured on Earth despite the differences in aeolian environment. Furthermore, ripples on dune flanks are shown to behave according to terrestrial models for ripple development on steep slopes. Compensating for these slope effects allows them to act as indicators of dune-modified and regional wind directions. Changes in ripple patterns and migration rates also signal the response of dunes and airflow during dune collisions. Collectively, we find that differences in ripple patterns connected to changes in migration rate provide information on airflow over and around dunes. This detailed assessment of ripple measurement and ripple migration rates advances the use of ripples on martian dunes and sand sheets to infer dune- and field-scale wind dynamics. These measurements also indicate that the low density atmosphere on Mars does not significantly modify the behavior of wind-topography interactions compared to Earth. Such observations provide targets for computational fluid dynamic and large-eddy simulation models seeking to reveal complex airflows across dune fields both on Earth and on Mars.

Additional Information

© 2021 Hood, Ewing, Roback, Runyon, Avouac and McEnroe. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Received: 30 April 2021; Accepted: 23 June 2021; Published: 12 July 2021. This work was funded primarily by the Mars Data Analysis Program (Grant #NNX16AJ43G). Data Availability Statement: The original contributions presented in the study are included in the Mendeley Data Repository: 10.17632/xk479zkpm8.1, further inquiries can be directed to the corresponding author. Author Contributions: DH was primarily responsible for writing the manuscript and was the primary researcher on the project. RE advised DH in the writing and research process. KR generated the COSI-Corr data used in the analysis. KR provided revisions on the manuscript and provided scientific guidance to the project. J-PA provided revisions on the manuscript and provided guidance on the application of the COSI-Corr methodology. MM aided in ripple tracing, providing data to the analysis. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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