Title: An integrated model for dune morphology and sand fluxes on Mars
Authors: Runyon, K. D.; Bridges, N. T.; Ayoub, F.; Newman, C. E.; Quade, J. J.
Affiliation: AA(Johns Hopkins University, Department of Earth and Planetary Sciences, 301 Olin Hall, 3400 N. Charles Street, Baltimore, MD 21218, USA 0000-0001-6361-6548), AB(Johns Hopkins University, Applied Physics Laboratory, Planetary Exploration Group, 11101 Johns Hopkins Road, Laurel, MD 20723, USA), AC(Geological and Planetary Sciences, California Institute of Technology, MC 100-23, Pasadena, CA 91125, USA), AD(Aeolis Research, 600 N. Rosemead Blvd., Suite 205, Pasadena, CA 91107, USA), AE(University of Maryland, James A. Clark School of Engineering, 4611 College Ave, College Park, MD 20740, USA)
Journal: Earth and Planetary Science Letters, Volume 457, p. 204-212.
Publication Date: Jan 2017
Keywords: aeolian, Mars, climate, stratigraphy, surface processes, GCM
Abstract Copyright: (c) 2017 Elsevier Science B.V. All rights reserved.
DOI: http://dx.doi.org/10.1016/j.epsl.2016.09.054http://bit.ly/2omsxBk
Bibliographic Code: 2017E&PSL.457..204R
Abstract: The transport and deposition of sand is the most prevalent agent of landscape modification on Mars today, with fluxes comparable to some sand dunes on Earth. Until now, the relationship between sand flux and dune field morphology has been poorly constrained. By tracking dune movement over ∼10 km-long dune fields in Herschel Crater and Nili Patera, representative of many dune fields on Mars, we find a downwind flux decrease that correlates with a sequence of changing morphology from barchans to barchanoids and seifs (longitudinal dunes) to isolated dome dunes and ending with sand sheets. We show empirical consistency with atmospheric Internal Boundary Layer (IBL) theory which can describe these broad flux and morphology changes in Martian dune fields. Deviations from IBL flux predictions are from wind streamline compressions up slopes, leading to a speedup effect. By establishing a dune field morphology type example and correlating it with measured and predicted flux changes, we provide an integrated morphology and flux model that can be applied to other areas of Mars and be used to infer paleo-environmental conditions from preserved sandstone.


Title: Winds measured by the Rover Environmental Monitoring Station (REMS) during Curiosity's Bagnold Dunes Campaign
Authors: Newman, Claire E.; Gomez-Elvira, Javier; Navarro Lopez, Sara; Marin Jimenez, Mercedes; Torres Redondo, Josefina; Richardson, Mark I.
Affiliation: AA(Aeolis Research), AB(Centro de Astrobiologia), AC(Centro de Astrobiologia), AD(Centro de Astrobiologia), AE(Centro de Astrobiologia), AF(Aeolis Research)
Journal: American Astronomical Society, DPS meeting #48, id.210.02
Publication Date: Oct 2016
Origin: AAS
Abstract Copyright: (c) 2016: American Astronomical Society
DOI: http://dx.doi.org/10.1016/j.icarus.2016.12.016http://bit.ly/2ohyIZJ
Bibliographic Code: 2016DPS....4821002N
Abstract: Curiosity's damaged wind sensor has trouble measuring winds coming from behind the rover, due to the loss of its side-pointing boom during landing. During the Bagnold Dunes Campaign, however, the rover was turned to permit measurements of winds from missing directions, capturing upslope/downslope day-night flow on the slopes of Aeolis Mons and blocking of wind in the lee of a dune.The rover's heading is generally determined by the drive direction and often varies little over many tens of sols. Good wind measurements are made when the wind comes from the hemisphere to the front of the rover, but there are sometimes long periods during which winds from certain directions (i.e., at certain times of sol) are largely missed. Since rover turns are often precluded by rover safety and other operational constraints, it is usually not possible to turn to measure such winds properly.During the Bagnold Dunes Campaign, wind measurements were prioritized to provide context for aeolian dune studies. Rover headings were optimized for three wind investigations covering a period of about 90 sols. The first investigation characterized the wind field on approach to the dunes, with the rover turned to face two unusual headings for several sols each and monitoring focused on the 'missing' winds / times of sol. This confirmed the expected primary wind pattern of daytime roughly upslope winds (from ~NW/N) and nighttime downslope winds (from ~S/SE) on the slopes of Aeolis Mons, with significant sol-to-sol variability in e.g. the timing of the reversals. Comparison with the previous year suggests an increasingly upslope-downslope pattern as Curiosity approached the slope.The second investigation studied changes to the wind pattern in the lee of the Namib Dune. This revealed the blocking of northerly winds by the large dune, leaving primarily a westerly component to the daytime winds with weaker wind speeds.The third investigation characterized the wind field at the side of Namib Dune. The rover heading was chosen to optimize daytime winds, in support of 'change detection' experiments that were designed to correlate strong winds with changes in surface grain positions imaged over periods ranging from a few hours to several sols.
Title: The influence of subsurface flow on lake formation and north polar lake distribution on Titan
Authors: Horvath, David G.; Andrews-Hanna, Jeffrey C.; Newman, Claire E.; Mitchell, Karl L.; Stiles, Bryan W.
Affiliation: AA(Colorado School of Mines, Department of Geophysics and Center for Space Resources, 1500 Illinois Street, Golden, CO 80401, USA), AB(Southwest Research Institute, 1050 Walnut St., Boulder, CO 80302, USA), AC(Ashima Research, Suite 104, 600 South Lake Avenue, Pasadena, CA 91106, USA), AD(Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA), AE(Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA)
Journal: Icarus, Volume 277, p. 103-124.
Publication Date: Oct 2016
Keywords: Titan, hydrology, surface
Abstract Copyright: (c) 2016 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2016.04.042http://bit.ly/2oDPIqa
Bibliographic Code: 2016Icar..277..103H
Abstract: Observations of lakes, fluvial dissection of the surface, rapid variations in cloud cover, and lake shoreline changes indicate that Saturn's moon Titan is hydrologically active, with a hydrocarbon-based hydrological cycle dominated by liquid methane. Here we use a numerical model to investigate the Titan hydrological cycle - including surface, subsurface, and atmospheric components - in order to investigate the underlying causes of the observed distribution and sizes of lakes in the north polar region. The hydrocarbon-based hydrological cycle is modeled using a numerical subsurface flow model and analytical runoff scheme, driven by a general circulation model with an active methane-cycle. This model is run on synthetically generated topography that matches the fractal character of the observed topography, without explicit representation of the effects of erosion and deposition. At the scale of individual basins, intermediate to high permeability (10-8-10-6 cm2) aquifers are required to reproduce the observed large stable lakes. However, at the scale of the entire north polar lake district, a high permeability aquifer results in the rapid flushing of methane through the aquifer from high polar latitudes to dry lower polar latitudes, where methane is removed by evaporation, preventing large lakes from forming. In contrast, an intermediate permeability aquifer slows the subsurface flow from high polar latitudes, allowing greater lake areas. The observed distribution of lakes is best matched by either a uniform intermediate permeability aquifer, or a combination of a high permeability cap at high latitudes surrounded by an intermediate permeability aquifer at lower latitudes, as could arise due to karstic processes at the north pole. The stability of Kraken Mare further requires reduction of the evaporation rate over the sea to 1% of the value predicted by the general circulation model, likely as a result of dissolved ethane, nitrogen, or organic solutes, and/or a climatic lake effect. These results reveal that subsurface flow through aquifers plays an important role in Titan's hydrological cycle, and exerts a strong influence over the distribution, size, and volatile budgets of Titan's lakes.
Title: Variations in Titan's dune orientations as a result of orbital forcing
Authors: McDonald, George D.; Hayes, Alexander G.; Ewing, Ryan C.; Lora, Juan M.; Newman, Claire E.; Tokano, Tetsuya; Lucas, Antoine; Soto, Alejandro; Chen, Gang
Affiliation: AA(School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30308, USA), AB(Department of Astronomy, Cornell University, Ithaca, NY 14853, USA), AC(Department of Geology and Geophysics, Texas A&M University, College Station, TX 77840, USA), AD(Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA), AE(Ashima Research, Pasadena, CA 91001, USA), AF(Institut für Geophysik und Meteorologie, Universität zu Köln, 50923 Köln, Germany), AG(AIM CEA-Saclay, Paris VII-Denis Diderot University, Paris 75013, France), AH(Southwest Research Institute, Boulder, CO 80032, USA), AI(Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, USA)
Journal: Icarus, Volume 270, p. 197-210.
Publication Date: May 2016
Keywords: Titan, Titan, surface, Titan, atmosphere, Atmospheres, dynamics
Abstract Copyright: (c) 2016 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2015.11.036http://bit.ly/2bk6dBp
Bibliographic Code: 2016Icar..270..197M
Abstract: Wind-blown dunes are a record of the climatic history in Titan's equatorial region. Through modeling of the climatic conditions associated with Titan's historical orbital configurations (arising from apsidal precessions of Saturn's orbit), we present evidence that the orientations of the dunes are influenced by orbital forcing. Analysis of 3 Titan general circulation models (GCMs) in conjunction with a sediment transport model provides the first direct intercomparison of results from different Titan GCMs. We report variability in the dune orientations predicted for different orbital epochs of up to 70°. Although the response of the GCMs to orbital forcing varies, the orbital influence on the dune orientations is found to be significant across all models. Furthermore, there is near agreement among the two models run with surface topography, with 3 out of the 5 dune fields matching observation for the most recent orbital cycle. Through comparison with observations by Cassini, we find situations in which the observed dune orientations are in best agreement with those modeled for previous orbital configurations or combinations thereof, representing a larger portion of the cycle. We conclude that orbital forcing could be an important factor in governing the present-day dune orientations observed on Titan and should be considered when modeling dune evolution.
Title: Atmospheric tides in Gale Crater, Mars
Authors: Guzewich, Scott D.; Newman, C. E.; de la Torre Juárez, M.; Wilson, R. J.; Lemmon, M.; Smith, M. D.; Kahanpää, H.; Harri, A.-M.
Affiliation: AA(CRESST and Planetary Systems Laboratory, NASA/GSFC, Greenbelt, MD 20771, United States), AB(Ashima Research, Pasadena, CA 91106, United States), AC(Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United States), AD(Geophysical Fluid Dynamics Laboratory, Princeton, NJ 08540, United States), AE(Texas A&M University, College Station, TX 77843, United States), AF(Planetary Systems Laboratory, NASA/GSFC, Greenbelt, MD 20771, United States), AG(Finnish Meteorological Institute, Helsinki, Finland), AH(Finnish Meteorological Institute, Helsinki, Finland)
Journal: Icarus, Volume 268, p. 37-49.
Publication Date: Apr 2016
Keywords: Mars, atmosphere, Atmospheres, dynamics, Meteorology
Abstract Copyright: (c) 2016 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2015.12.028http://bit.ly/2boX8dS
Bibliographic Code: 2016Icar..268...37G
Abstract: Atmospheric tides are the primary source of daily air pressure variation at the surface of Mars. These tides are forced by solar heating of the atmosphere and modulated by the presence of atmospheric dust, topography, and surface albedo and thermal inertia. This results in a complex mix of sun-synchronous and non-sun-synchronous tides propagating both eastward and westward around the planet in periods that are integer fractions of a solar day. The Rover Environmental Monitoring Station on board the Mars Science Laboratory has observed air pressure at a regular cadence for over 1 Mars year and here we analyze and diagnose atmospheric tides in this pressure record. The diurnal tide amplitude varies from 26 to 63 Pa with an average phase of 0424 local true solar time, while the semidiurnal tide amplitude varies from 5 to 20 Pa with an average phase of 0929. We find that both the diurnal and semidiurnal tides in Gale Crater are highly correlated to atmospheric opacity variations at a value of 0.9 and to each other at a value of 0.77, with some key exceptions occurring during regional and local dust storms. We supplement our analysis with MarsWRF general circulation modeling to examine how a local dust storm impacts the diurnal tide in its vicinity. We find that both the diurnal tide amplitude enhancement and regional coverage of notable amplitude enhancement linearly scales with the size of the local dust storm. Our results provide the first long-term record of surface pressure tides near the martian equator.
Title: Simulating Titan's methane cycle with the TitanWRF General Circulation Model
Authors: Newman, Claire E.; Richardson, Mark I.; Lian, Yuan; Lee, Christopher
Affiliation: AA(Aeolis Research, Suite 205, 600 North Rosemead Boulevard, Pasadena, CA 91107, USA), AB(Aeolis Research, Suite 205, 600 North Rosemead Boulevard, Pasadena, CA 91107, USA 0000-0001-9633-4141), AC(Aeolis Research, Suite 205, 600 North Rosemead Boulevard, Pasadena, CA 91107, USA), AD(Aeolis Research, Suite 205, 600 North Rosemead Boulevard, Pasadena, CA 91107, USA)
Journal: Icarus, Volume 267, p. 106-134.
Publication Date: Mar 2016
Keywords: Titan, Titan, atmosphere, Atmospheres, dynamics, Atmospheres, structure, Meteorology
Abstract Copyright: (c) 2016 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2015.11.028http://bit.ly/22fPJwT
Bibliographic Code: 2016Icar..267..106N
Abstract: Observations provide increasing evidence of a methane hydrological cycle on Titan. Earth-based and Cassini-based monitoring has produced data on the seasonal variation in cloud activity and location, with clouds being observed at increasingly low latitudes as Titan moved out of southern summer. Lakes are observed at high latitudes, with far larger lakes and greater areal coverage in the northern hemisphere, where some shorelines extend down as far as 50°N. Rainfall at some point in the past is suggested by the pattern of flow features on the surface at the Huygens landing site, while recent rainfall is suggested by surface change. As with the water cycle on Earth, the methane cycle on Titan is both impacted by tropospheric dynamics and likely able to impact this circulation via feedbacks. Here we use the 3D TitanWRF General Circulation Model (GCM) to simulate Titan's methane cycle. In this initial work we use a simple large-scale condensation scheme with latent heat feedbacks and a finite surface reservoir of methane, and focus on large-scale dynamical interactions between the atmospheric circulation and methane, and how these impact seasonal changes and the long term (steady state) behavior of the methane cycle. We note five major conclusions: (1) Condensation and precipitation in the model is sporadic in nature, with interannual variability in its timing and location, but tends to occur in association with both (a) frequent strong polar upwelling during spring and summer in each hemisphere, and (b) the Inter-Tropical Convergence Zone (ITCZ), a region of increased convergence and upwelling due to the seasonally shifting Hadley cells. (2) An active tropospheric methane cycle affects the stratospheric circulation, slightly weakening the stratospheric superrotation produced. (3) Latent heating feedback strongly influences surface and near-surface temperatures, narrowing the latitudinal range of the ITCZ, and changing the distribution - and generally weakening the strength - of upwelling events. (4) TitanWRF favors low latitude 'cloudiness' around northern spring equinox as the ITCZ moves from south to north across the equator, versus the opposite time of year. (5) TitanWRF produces drying of low and mid latitudes with net transport of surface methane to high latitudes, and shows persistent hemispheric asymmetry in the methane cycle such that the favored pole for surface methane is the one with winter occurring closest to perihelion.