Figure 3
Regions of moderate-and high-sand-flux dune fields (graduated circles with same color scheme as Fig. 2). Legend in bottom map applies to all panels. Average dune migration vectors are represented by black arrows for each dune field. Dune field distributions are shown in red. Inset High Resolution Imaging Science Experiment (HiRISE) images are ~2 km wide. Base maps are Mars Orbiter Laser Altimeter (MOLA) shaded relief with colorized elevation from +4 (red) to-5 km (blue), except for the north polar map, which ranges from-2 to-7 km. Compare with Figure 4.
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Wind has been an enduring geologic agent throughout the history of Mars, but it is often unclear where and why sediment is mobile in the current epoch. We investigated whether eolian bed-form (dune and ripple) transport rates are depressed or enhanced in some areas by local or regional boundary conditions (e.g., topography, sand supply/availability...
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Taking advantage of alternative expressions for potential vorticity (PV) in divergence forms, we derive balances between volume integral of PV and boundary conditions, that are then applied to practical computations of PV: - we propose a new method for diagnosing the Ertel potential vorticity from model output, that preserves the balances; - we sho...
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... This is a critical issue, as for instance the InSight Mars lander (IML) was finally retired due to the dust accumulated on its solar panels, limiting the power supply. 4. Improving the knowledge of aeolian activity (dust lifting, regional-scale sand transport, dune formation, etc.) and resulting impacts on Martian geomorphology, weather, and climate Chen-Chen et al., 2023;Chojnacki et al., 2019;Newman et al., 2022;Savijäarvi, 1999;Swann et al., 2020). ...
... Hence, in many sites, these flows greatly affect processes such as the surface pressure diurnal cycle (Tyler Jr et al., 2002), near-surface winds, aeolian activity, etc. For example, this occurs in Arsia Mons (Savijärvi & Siili, 1993), Hellas basin (Fazel-Rastgar, 2019;Newman et al., 2002aNewman et al., , 2002b, Argyre basin (Fazel-Rastgar, 2019), Hellespontus Montes, Hellas and Isidis Planitia (Chojnacki et al., 2019), Chryse and Utopia Planitia, landing sites of the Viking lander 1 and 2 (VL1 and VL2), respectively (Haberle et al., 1993), Valles Marineris, landing site of the Mars Pathfinder (MPF) rover (Tyler Jr et al., 2002), Aeolis Mons in Gale Crater, landing site of the Mars Science Laboratory (MSL)/Curiosity rover (Baker et al., 2018;Kite et al., 2013;Newman et al., 2017;Pla-García et al., 2016;Rafkin et al., 2016;Richardson & Newman, 2018;Soria-Salinas et al., 2020), and Jezero Crater, landing site of the Mars 2020 Perseverance rover (Pla-García et al., 2020;Viúdez-Moreiras, de la Torre, et al., 2022;Viúdez-Moreiras, Lemmon, et al., 2022). The magnitude and timing of the winds predicted and measured Viúdez-Moreiras, Lemmon, et al., 2022) in Jezero are reported to be consistent with primary control by regional and local slope flows. ...
Regional and local thermally driven winds are planetary boundary layer phenomena frequently observed on Mars over sloping and flat regions, when diurnal surface temperature variations are significant and large‐scale winds are sufficiently weak. In particular, slope flows are prevalent in many areas on Mars, where they can reach high speeds and have a substantial impact on the near‐surface wind patterns, pressure diurnal cycle, aeolian activity, etc. This work first reviews literature on Martian winds, listing wind speeds obtained either numerically or from in situ measurements, with special emphasis on slope flows. Second, a methodology is presented to perform numerical simulations of slope flows on Mars using the open‐source computational fluid dynamics code OpenFOAM. Slope winds are then studied in a simplified Martian mountain‐valley configuration, using realistic values for various parameters, such as the slope angle and temperature variation. The incompressible Navier‐Stokes equations with Boussinesq approximation are used, along with the k‐ɛ Reynolds‐averaged Navier‐Stokes turbulence model. Radiant heat transfer is included and proven to be paramount for a correct description of Martian slope winds. Results of velocity and temperature profiles are obtained for various slope angles. These simulations aim to provide further insight on the behavior of slope winds on Mars, to simplify the process of assessing numerous potential landing sites for upcoming missions, since these highly regular winds could be useful, for instance, for dust removal applications.
... Ripple activity depends not only on wind strength and frequency of strong wind events but also on the availability of fine and medium sand. If fine and medium sand is not available, even bedforms composed of fine sand are dormant ; but when a high flux of such particles is present, even bedforms composed of coarse grains can be activated (Chojnacki et al., 2019;Silvestro et al., 2020). In modern times, the supply of fine and medium sand particles on Meridiani Planum is low, as there are almost no medium sand particles on the Meridiani Planum plains and fine sand particles were immobilized under armoring layers of lag deposits and within coarsegrained ripples . ...
Aeolian coarse‐grained ripples have been found in all regions investigated by Mars rovers: Meridiani Planum, Gusev crater, Gale crater, and Jezero crater. Therefore, it can be assumed that coarse‐grained ripples are one of the most common landforms on Mars. Studying their formation and evolution gives us the opportunity to determine past and current wind patterns. They are also crucial for understanding the formation and evolution of larger aeolian bedforms. Of all locations studied in situ on Mars, coarse‐grained ripples in extensive (∼100 km²) ripple fields were found only on Meridiani Planum. As coarse‐grained ripples on Mars are not well characterized in the literature, in this work, the morphometry, morphology, spatial distribution, and orientation of coarse‐grained ripples investigated along the 45 km long traverse of the Opportunity rover were analyzed. The obtained results allowed for a more precise definition of coarse‐grained ripples and for distinguishing three classes of coarse‐grained ripples on Meridiani Planum: small, medium, and large. The coarse‐grained ripple activity on Meridiani Planum is now limited due to low material supply, and the relatively strong induration of the ripple surfaces. Even though most of the coarse‐grained ripples on Meridiani Planum were formed thousands of years ago, some smaller coarse‐grained ripples were formed by modern winds.
... In other places, such as in northern Terra Sabaea from Meridiani Planum to Syrtis Major (approximately 0-45°N; 0-60°E), GCM predictions are poorly aligned with (and in some places are even opposite to) our measured dune-migration directions from barchan morphology-even though the dunes themselves appear to follow continuous pathways. Further inspection of repeat High Resolution Imaging Experiment (HiRISE) imagery (Chojnacki et al., 2019) reveals that the modern migration direction of meter-scale ripples, superimposed onto the barchan dunes, agrees 10.1029/2022GL102610 6 of 12 with inferred dune-migration direction, thus ruling out the possibility that dune morphology in that region does not reflect contemporaneous wind conditions. In addition, estimated dune reconstitution timescales suggest that most barchan dunes would reorient faster than known orbital forcings, further supporting that observed dune orientations reflect modern wind conditions ( Figure S4). ...
... Regardless of spatial bin size, we find a consistent correlation between σ and δ for topographic baselines smaller than ∼10-50 km (Figures 3b and 3c), suggesting that at those scales, dune migration is influenced by winds induced or diverted by local topography (Chojnacki et al., 2019;Hess et al., 1977;Parteli et al., 2014;Rubanenko, Powell, et al., 2021). The strength of the correlation between σ and δ decreases as the topographic baseline increases, until it ceases to be statistically significant for horizontal scales >100 km. ...
... South of −45°N, flow is mostly to the north, with a strong zonal component in the mid-latitudes of both hemispheres. The higher scatter in this region could potentially be related to lower dune migration rates, as observed for example, in Green crater or Aonia Terra (Banks et al., 2018;Chojnacki et al., 2019). ...
In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind directions. Here, we characterize near‐surface winds on Mars from the morphology of >700,000 barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with known southern‐summer atmospheric circulation patterns—northerly at mid‐latitudes and cyclonic near the north pole—with the addition of an anti‐cyclonic north‐polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles <100 km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary‐scale aeolian processes on modern‐day Mars, can be used to constrain global circulation models to assist with predictions for future missions.
... Micro-(ripples) and macro-scale (dunes) bedform migration serve as one of the most direct confirmations of wind playing a key role in shaping the surface of Mars (e.g., Silvestro and Titus, 2022). While across latitudes, presence of a large number of sand dunes (Fenton, 2006;Silvestro et al., 2010;Bridges et al., 2013;Chojnacki et al., 2019) and transverse aeolian ridges (TARs) (Balme et al., 2008;Bridges et al., 2012Bridges et al., , 2013 have been documented from remote sensing observations, identifying appreciable bedform movement in medium resolution images has been challenging. This is owing to the fact that the threshold friction speeds for saltation are considerably high in some areas, such that in some places migration rates could be as low as 1-2 cm or less, every Mars Year (Fenton, 2006;Fenton et al., 2021). ...
... This is owing to the fact that the threshold friction speeds for saltation are considerably high in some areas, such that in some places migration rates could be as low as 1-2 cm or less, every Mars Year (Fenton, 2006;Fenton et al., 2021). This however, is also very region-dependent, as topography plays a crucial role in triggering aeolian activity on Mars (Fenton et al., 2013;Vaz et al., 2017;Chojnacki et al., 2019). Thus, greater sediment transport rates on Mars have been observed in the north polar erg, Hellespontus Montes, and the Syrtis Major volcanic province (Ayoub et al., 2014;Chojnacki et al., 2019;Dundas et al., 2021), and even bright-toned megaripples have been observed to move (Silvestro et al., 2020;Chojnacki et al., 2021). ...
... This however, is also very region-dependent, as topography plays a crucial role in triggering aeolian activity on Mars (Fenton et al., 2013;Vaz et al., 2017;Chojnacki et al., 2019). Thus, greater sediment transport rates on Mars have been observed in the north polar erg, Hellespontus Montes, and the Syrtis Major volcanic province (Ayoub et al., 2014;Chojnacki et al., 2019;Dundas et al., 2021), and even bright-toned megaripples have been observed to move (Silvestro et al., 2020;Chojnacki et al., 2021). ...
Mars is host to a variety of active surface processes that relate to changes in seasonal ice/frost, slope activity, wind and processes potentially relating to liquid water. Regular monitoring and change detection of these phenomena is crucial to not only provide us insights into present day Martian surface conditions, but also its past geologic and climatic scenarios. Visual comparisons of high-resolution remote sensing images of the surface from the Mars Reconnaissance Orbiter (MRO) have allowed detailed tracking and monitoring of these changes over time. The CaSSIS instrument onboard the ExoMars Trace Gas orbiter also provides a unique pathway to track areally-large surface changes in colour, that permits us to better constrain origin and evolution of various surface features. Since TGO operates in a non-sun-synchronous orbit, previously adopted qualitative methods like visual image comparisons for MRO cannot be adopted for CaSSIS-based change detection. Consequently, this study lists and describes in detail, the techniques that need to be adopted to conduct such change detection campaigns with CaSSIS, for the variety of active processes currently identified on Mars. This work also proposes and describes two additional semi-quantitative techniques for CaSSIS-based change detection, that may be used in concert with existing visual comparison methods to enable reliable change identification and tracking. It is observed that these supplementary methods work well in characterizing a variety of surface changes related to ice/frost and slope processes, and can provide reasonable spectral constraints to better understand their origin. These methods are not effective in providing quantitative constraints for purely physical changes. Instead, for long-period changes like aeolian bedform movement, digital image correlation techniques on ortho-rectified images, are recom- mended; while for short period changes like real-time dust devil activity, measurements based on CaSSIS stereo pairs of the region can be used to provide quantitative estimates of change.
... Sand and dust are mobile on the surface of Mars, readily observable from small scale dust devils over sand dune motion to global dust storms (Fenton 2020;Viúdez-Moreiras et al. 2020;Toigo et al. 2018;Lorenz et al. 2021;Heyer et al. 2020;Chojnacki et al. 2019). This requires some lifting mechanism and gas drag related to wind and eolian transport is undoubtedly a main driver (Rasmussen et al. 2015). ...
At low ambient pressure, temperature gradients in porous soil lead to a gas flow, called thermal creep. With this regard, Mars is a unique as the conditions for thermal creep to occur in natural soil only exist on this planet in the solar system. Known as Knudsen compressor, thermal creep induces pressure variations. In the case of Mars, there might be a pressure maximum below the very top dust particle layers of the soil, which would support particle lift and might decrease threshold wind velocities necessary to trigger saltation or reduce angles of repose on certain slopes. In laboratory experiments, we applied diffusing wave spectroscopy (DWS) to trace minute motions of grains on the nm-scale in an illuminated simulated soil. This way, DWS visualizes pressure variations. We observe a minimum of motion which we attribute to the pressure maximum ~ 2 mm below the surface. The motion above but especially below that depth characteristically depends on the ambient pressure with a peak at an ambient pressure of about 3 mbar for our sample. This is consistent with earlier work on ejection of particle layers and is in agreement to a thermal creep origin. It underlines the supporting nature of thermal creep for particle lift which might be especially important on Mars.
... Sand and dust are mobile on the surface of Mars, readily observable from small-scale dust devils over sand dune motion to global dust storms (Toigo et al. 2018;Chojnacki et al. 2019;Fenton 2020;Heyer et al. 2020; Viúdez-Moreiras 2020; Lorenz et al. 2021). This requires some lifting mechanism and gas drag related to wind and eolian transport is undoubtedly a main driver (Rasmussen 2015). ...
At low ambient pressure, temperature gradients in porous soil lead to a gas flow called thermal creep. In this regard, Mars is unique as the conditions for thermal creep to occur in natural soil only exist on this planet in the solar system. Known as a Knudsen compressor, thermal creep induces pressure variations. In the case of Mars, there might be a pressure maximum below the very top dust particle layers of the soil, which would support particle lift and might decrease threshold wind velocities necessary to trigger saltation or reduce angles of repose on certain slopes. In laboratory experiments, we applied diffusing wave spectroscopy (DWS) to trace minute motions of grains on the nanometer scale in an illuminated simulated soil. This way, DWS visualizes pressure variations. We observe a minimum of motion, which we attribute to the pressure maximum ∼2 mm below the surface. The motion above but especially below that depth characteristically depends on the ambient pressure with a peak at an ambient pressure of about 3 mbar for our sample. This is consistent with earlier work on the ejection of particle layers and is in agreement with a thermal creep origin. It underlines the supporting nature of thermal creep for particle lift, which might be especially important on Mars.
... In other places, such as in northern Terra Sabaea from Meridiani Planum to Syrtis Major (approximately 0-45°N; 0-60°E), GCM predictions are poorly aligned with (and in some places are even opposite to) our measured dune-migration directions from barchan morphology-even though the dunes themselves appear to follow continuous pathways. Further inspection of repeat High Resolution Imaging Experiment (HiRISE) imagery (Chojnacki et al., 2019) reveals that the modern migration direction of meter-scale ripples, superimposed onto the barchan dunes, agrees 10.1029/2022GL102610 6 of 12 with inferred dune-migration direction, thus ruling out the possibility that dune morphology in that region does not reflect contemporaneous wind conditions. In addition, estimated dune reconstitution timescales suggest that most barchan dunes would reorient faster than known orbital forcings, further supporting that observed dune orientations reflect modern wind conditions ( Figure S4). ...
... Regardless of spatial bin size, we find a consistent correlation between σ and δ for topographic baselines smaller than ∼10-50 km (Figures 3b and 3c), suggesting that at those scales, dune migration is influenced by winds induced or diverted by local topography (Chojnacki et al., 2019;Hess et al., 1977;Parteli et al., 2014;Rubanenko, Powell, et al., 2021). The strength of the correlation between σ and δ decreases as the topographic baseline increases, until it ceases to be statistically significant for horizontal scales >100 km. ...
... South of −45°N, flow is mostly to the north, with a strong zonal component in the mid-latitudes of both hemispheres. The higher scatter in this region could potentially be related to lower dune migration rates, as observed for example, in Green crater or Aonia Terra (Banks et al., 2018;Chojnacki et al., 2019). ...
In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind direction. Here, we characterize near-surface winds on Mars from the morphology of >106 barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with the global circulation: northerly at mid-latitudes and cyclonic near the north pole, with the addition of an anti-cyclonic north-polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles <100 km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary-scale aeolian processes on modern-day Mars, can be used to constrain global circulation models to assist with predictions for future missions.
... This is consistent with our previous observation that intracrater plains generally exhibit lower WEP values. Despite the low WEP relative to the other sites, Jezero exhibits evidence for extensive aeolian erosion (e.g., Day & Dorn, 2019;Fassett & Head, 2005;Schon et al., 2012) and high modern sediment fluxes (Chojnacki et al., 2019). ...
... As shown in previous work, there is strong evidence for aeolian erosion in Jezero crater (e.g., Chojnacki et al., 2019;Fassett & Head, 2005;Schon et al., 2012;Day & Dorn, 2019). Repeat HiRISE observations of dunes in both Jezero crater and Syrtis Major also show moderate to high sand flux values compared to other regions on Mars (Chojnacki et al., 2019). ...
... As shown in previous work, there is strong evidence for aeolian erosion in Jezero crater (e.g., Chojnacki et al., 2019;Fassett & Head, 2005;Schon et al., 2012;Day & Dorn, 2019). Repeat HiRISE observations of dunes in both Jezero crater and Syrtis Major also show moderate to high sand flux values compared to other regions on Mars (Chojnacki et al., 2019). Although wind erosion is clearly occurring within Jezero, our models predict relatively low annual WEP on the MFU compared to volcanic plains in Hesperia Planum and Syrtis Major Planum, and do not predict differences in WEP across the "fractured rough" and "fractured smooth" MFU subunit boundary. ...
The Martian highlands contain Noachian‐aged areally‐extensive (>225 km²) bedrock exposures that have been mapped using thermal and visible imaging datasets. Given their age, crater density and impact gardening should have led to the formation of decameter scale layers of regolith that would overlie and bury these outcrops if composed of competent materials like basaltic lavas. However, many of these regions lack thick regolith layers and show clear exposures of bedrock materials with elevated thermal inertia values compared to the global average. Hypothesized reasons for the lack of regolith include: (a) relatively weaker material properties than lavas, where friable materials are comminuted and deflated during wind erosion, (b) long‐term protection from regolith development through burial and later exhumation through one or more surface processes, and (c) spatially concentrated aeolian erosion and wind energetics on well‐lithified basaltic substrates. To test the third hypothesis, we used the Mars Regional Atmospheric Modeling System to calculate wind erosive strength at 10 regions throughout the Martian highlands and compared it to their thermophysical properties by using thermal infrared data derived from the Thermal Emission Spectrometer to understand the effect that Amazonian mesoscale wind patterns may have on the exposure of bedrock. We also investigated the effect of planet obliquity, Ls of perihelion, and atmospheric mean pressure on wind erosion potential. We found no evidence for increased aeolian activity over bedrock‐containing regions relative to surrounding terrains, including at the mafic floor unit at Jezero crater (Máaz formation), supporting the first or second hypotheses for these regions.
... Modelling of superimposed small impact ripples was carried out by studying their development from small random perturbations on the large well-developed ripples. Another experiment goal was to compare between the modeled reptation flux and reptation flux calculated from observed Martian ripple migration [25]. This time scale is important for understanding the origin of large ripples in the framework of the impact ripple hypothesis. ...
Ripples made from unimodal fine sands can grow much larger on Mars than on Earth, reaching wavelengths of 1–3 m and heights exceeding 1 dm. Smaller decimeter-wavelength ripples can be superimposed on them. Classification and origins of these bedforms have been debated. They have been interpreted as analogous to subaqueous ripples on Earth, or as aeolian impact ripples with a range of grain sizes that reach large maximum sizes on Mars. This study uses a mathematical model to evaluate the formation of large Martian ripples as aeolian impact ripples to further investigate this hypothesis. The model parameters were computed using COMSALT for 100 µm grains under shear velocity of 0.65 m/s, which is a reasonable shear velocity for sand transport on Mars according to recent estimations of threshold Martian winds. The numerical experiments utilize a large grid 8 m long. Experiments also evaluate the development of secondary small ripples between the large ripples from random perturbations. The numerical simulations show the evolution of ripple wavelength and height. According to the results, the time scale for the formation of the large ripples is about 2–3 years, which is a much longer time scale compared to terrestrial impact ripples. Small secondary ripples develop only if the space between the large ripples is sufficiently large.
... We also have to consider the high sand-flux, with dune migration rate up to ∼2 m/MY, at Olympia Undae as driven by summer katabatic winds modulated by the receding SNPC, large topographic relief, and large thermal contrast (Bridges et al., 2012;Chojnacki et al., 2019). The dune migration directions are determined by the katabatic winds and steered zonally by Coriolis-force winds, which can spatially vary . ...
Plain Language Summary
Due to its axial tilt, seasons also exist on Mars. Up to one third of the atmosphere's CO2 is in annual exchange with the polar regions through seasonal deposition/sublimation processes. Here, we make use of previously proposed approaches of analyzing the Mars Orbiter Laser Altimeter profiles and obtain spatio‐temporal level variations of the Seasonal North Polar Cap (SNPC). Particularly, we bring attention to abnormal behavior of the SNPC in the dune fields at Olympia Undae. Maximum level there can be all the way up to 4 m which is much higher than a maximum of 1.5 m over the Residual North Polar Cap. Meanwhile, off‐season decreases during the northern winter with magnitudes up to 3 m and off‐season increases during the northern spring of magnitudes up to 2 m are observed. These could possibly be related to metamorphism of the seasonal deposits and phased snowfall. The maximum volume of the SNPC is constrained to be 9.6 × 10¹² m³. The bulk density of the SNPC does not continuously increase as previously assumed but can go through phased decreases in accordance with phased snowfall at the north pole. These findings can put important constraints on the Martian climate models.
