A Mesoscale Modelling Approach to understanding Mars’ Aeolian Landscapes

Introduction: For decades, global climate models (GCMs) have played a foundational role in understanding Mars’s climate system, and more recently, have become integral to mission planning and interpreting spacecraft observations of atmospheric dynamics and landscape-level evidence of the aeolian (wind-driven) environment. 

Aeolian bedforms and landforms on Mars - from centimetre-scale ripples forming atop sand dunes to kilometre-scale yardangs all pointing in a single cardinal direction - constitute vital proxies to deciphering the spatially diverse and temporally extensive influence of wind across the planet. However, the scale of the aeolian features being investigated rarely align with the scale of the GCM being used (with typical spatial resolutions of hundreds of kilometres). For studies that investigate aeolian features at local and regional scales, higher resolution models - mesoscale models - are necessary to more fully understand the climatic conditions at scales that better represent the features being studied.  

Aims of this Work: The work presented here describes this group’s commitment to providing Mars researchers access to reliable wind data at topographically relevant scales for use in targeted studies of the Martian surface. To demonstrate the validity and practicality of our approach, we compare our mesoscale model outputs with mapped aeolian features at three sites on Mars: Mawrth Vallis (dune slip faces), Ares Vallis (wind streaks), and Syrtis Major (wind streaks). 

Mapping Aeolian Features: Dune slip faces and wind streaks were mapped on the ~6 m/pixel CTX (Context Camera) global mosaic [1] in a GIS. At Mawrth Vallis, we digitized the slip faces of 80 dunes in an area of approximately 544 km2. At Ares Vallis (~41,000 km2) and Syrtis Major (~6.7 million km2), we mapped 180 and 1000 kilometre-scale wind streaks, respectively.

Setting up the Mesoscale Models: The Open access to Mars Assimilated Remote Soundings (OpenMARS) dataset [2] provides the initial and hourly-updated boundary conditions for the mesoscale simulations. OpenMARS is a reference dataset of the actual global weather occurring on Mars from 1999 to 2020 at 5° horizontal resolution in longitude and latitude that has been utilized across the globe for several different science topics [3-8]; this study is the first dedicated to interpretation of aeolian surface features. The OpenMARS dataset combines the Mars Planetary Climate Model UK-spectral version (that has identical physics packages with the mesoscale model for optimal coupling) with temperature and dust retrievals from the Mars Climate Sounder instrument [9] to provide the most accurate global atmospheric representation possible.  Boundary conditions are updated for the mesoscale simulations every hour to guide the near-surface atmosphere that undergoes a strong daily cycle.

Mesocale simulations were performed using the Laboratoire de Météorologie Dynamique Mars Mesoscale Model [10]. This model combines the compressible non-hydrostatic dynamical core of the Advanced Research Weather Research and Forecasting model, adapted for Mars, with a comprehensive set of physics routines for simulating the CO2, dust, water and photochemical cycles of the Martian atmosphere. We configured the mesoscale model to run with 40 unevenly spaced levels from the surface up to 50 km. A 3000 by 3000 km domain was evaluated at Syrtis Major at a horizontal resolution of 14 km; a 1000 by 1000 km domain was used at the other locations at a horizontal resolution of 5 km. At each location, we performed four sets of simulations, each lasting 12 sols and starting at a different time of year (initialised at LS= 0°, 90°, 180° and 270°), to capture seasonal variability. The data from the four simulations were combined and mean eastward and northward winds calculated for each grid point. 

Results: Detailed results of our modelling exercises at these sites will be presented at this meeting. Briefly, our outputs show good agreement between aeolian feature orientation and the mesoscale near-surface annual mean wind flow and confirms that the modelling described here is appropriate for investigating contemporary aeolian features on Mars. 

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