Title: The impact of surface dust source exhaustion on the martian dust cycle, dust storms and interannual variability, as simulated by the MarsWRF General Circulation Model
Authors: Newman, Claire E.; Richardson, Mark I.
Affiliation: AA(Ashima Research, Suite 104, 600 South Lake Avenue, Pasadena, CA 91001, USA), AB(Ashima Research, Suite 104, 600 South Lake Avenue, Pasadena, CA 91001, USA)
Journal: Icarus, Volume 257, p. 47-87.
Publication Date: Sep 2015
Keywords: Mars, atmosphere, surface, Atmospheres, dynamics, climate
Abstract Copyright: (c) 2015 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2015.03.030http://bit.ly/2bk6IeS
Bibliographic Code: 2015Icar..257...47N
Abstract: Observations of albedo on Mars suggest a largely invariant long-term mean surface dust distribution, but also reveal variations on shorter (seasonal to annual) timescales, particularly associated with major dust storms. We study the impact of finite surface dust availability on the dust cycle in the MarsWRF General Circulation Model (GCM), which uses radiatively active dust with parameterized 'dust devil' and wind stress dust lifting to enable the spontaneous production of dust storms, and tracks budgets of dust lifting, deposition, and total surface dust inventory. We seek a self-consistent, long-term 'steady state' dust cycle for present day Mars, consisting of (a) a surface dust distribution that varies from year to year but is constant longer-term and in balance with current dust redistribution processes, and (b) a fixed set of dust lifting parameters that continue to produce major storms for this distribution of surface dust. We relax the GCM's surface dust inventory toward this steady state using an iterative process, in which dust lifting rate parameters are increased as progressively more surface sites are exhausted of dust. Late in the equilibration process, the GCM exhibits quasi-steady state behavior in which few new surface grid points are exhausted during a 60 year period with constant dust lifting parameters. Complex regional-scale dust redistribution occurs on time-scales from less than seasonal to decadal, and the GCM generates regional to global dust storms with many realistic features. These include merging regional storms, cross-equatorial storms, and the timing and location of several storm types, though very early major storms and large amounts of late storm activity are not reproduced. Surface dust availability in key onset and growth source regions appears vital for 'early' major storms, with replenishment of these regions required before another large storm can occur, whereas 'late' major storms appear primarily dependent on atmospheric variability. For the parameter space explored, no simulation achieves a steady state with continuing major storms lasting longer than 60 years when a constant wind stress lifting threshold is used. However, such a long-term steady state is achieved when a variable threshold is introduced, in which the threshold increases as dust is removed. This negative feedback on lifting slows it sufficiently for a balance to be produced between dust removal and re-deposition, even in key source regions for major storms. One concern is that the long-term surface dust distributions produced in these simulations show significant differences to the observed northern hemisphere albedo map, in particular predicting Tharsis and NE Arabia to be relatively dust-free. Although some observed high albedo regions may not have significant mobile dust, others likely have a dust cover several meters thick. The mismatches may reflect deficiencies in the GCM or the iterative process used, or the existence of ancient deep dust deposits formed during a past climate epoch.
Title: Twilight on Ligeia: Implications of communications geometry and seasonal winds for exploring Titan's seas 2020-2040
Authors: Lorenz, Ralph D.; Newman, Claire E.
Affiliation: AA(Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA), AB(Ashima Research, 600 S. Lake Ave., Suite 303, Pasadena, CA 91106, USA)
Journal: Advances in Space Research, Volume 56, Issue 1, p. 190-204.
Publication Date: Jul 2015
Keywords: Titan, Mission design, Direct-to-Earth communications, Wind dispersions, Navigation
Abstract Copyright: (c) 2015 COSPAR
DOI: http://dx.doi.org/10.1016/j.asr.2015.03.034http://bit.ly/2ojqON1
Bibliographic Code: 2015AdSpR..56..190L
Abstract: Titan's lakes and seas are targets of particular interest for future exploration. We review candidate splashdown areas in Ligeia and Kraken Mare, and Ontario Lacus. Titan's thick and dense atmosphere means that landing dispersions of spacecraft are dominated by uncertainties in wind drift, and thus the feasibility of landing safely in the sea with a simple Huygens-like descent system (i.e. without guidance or propulsion) is dependent upon these uncertainties being small enough that the landing point dispersion lies within the sea. Because Titan's winds vary with season, notably through the formation of a high-speed stratospheric jet in the winter hemisphere, landing point dispersions are seasonally-dependent as well as latitude-dependent. Ligeia Mare, at 78oN, sees relatively small dispersions but offers viable Direct-to-Earth (DTE) communication only until 2024. A wide part of Kraken Mare (450 × 90 km) at 70oN can be comfortably reached at all times, and is viable for assured Direct-to-Earth communication until 2026, or with a relay spacecraft thereafter. The seasonal geometry permits DTE from the northern seas again after 2040. Wind dispersions are always too large for Ontario, unless a steerable parachute or similar system is used to tighten the landing ellipse.
Title: General circulation models of the dynamics of Pluto's volatile transport on the eve of the New Horizons encounter
Authors: Toigo, Anthony D.; French, Richard G.; Gierasch, Peter J.; Guzewich, Scott D.; Zhu, Xun; Richardson, Mark I.
Affiliation: AA(Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, United States), AB(Wellesley College, Wellesley, MA 02492, United States), AC(Astronomy Department, Cornell University, Ithaca, NY 14853, United States), AD(NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States), AE(Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, United States), AF(Ashima Research, Pasadena, CA 91106, United States)
Journal: Icarus, Volume 254, p. 306-323.
Publication Date: Jul 2015
Keywords: Pluto, atmosphere, Atmospheres, dynamics
Abstract Copyright: (c) 2015 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2015.03.034http://bit.ly/2b2IhC3
Bibliographic Code: 2015Icar..254..306T
Abstract: Pluto's atmospheric dynamics occupy an interesting regime in which the radiative time constant is quite long, the combined effects of high obliquity and a highly eccentric orbit can produce strong seasonal variations in atmospheric pressure, and the strong coupling between the atmosphere and volatile transport on the surface results in atmospheric flows that are quite sensitive to surface and subsurface properties that at present are poorly constrained by direct observations. In anticipation of the New Horizons encounter with the Pluto system in July 2015, we present a Pluto-specific three-dimensional general circulation model (GCM), PlutoWRF, incorporating the most accurate current radiative transfer models of Pluto's atmosphere, a physically robust treatment of nitrogen volatile transport, and the flexibility to accommodate richly detailed information about the surface and subsurface conditions as new data become available. We solve for a physically self-consistent, equilibrated combination of surface, subsurface, and atmospheric conditions to specify the boundary conditions and initial state values for each GCM run. This is accomplished using two reduced versions of PlutoWRF: a two-dimensional surface volatile exchange model to specify the properties of surface nitrogen ice and the initial atmospheric surface pressure, and a one-dimensional radiative-conductive-convective model that uses the two-dimensional model predictions to determine the corresponding global-mean atmospheric thermal profile. We illustrate the capabilities of PlutoWRF in predicting Pluto's general circulation, thermal state, and volatile transport of nitrogen by calculating the dynamical response of Pluto's atmosphere, based on four different idealized models of Pluto's surface ice distribution from Young (Young, L.A. [2013]. Astrophys. J. 766, L22) and Hansen et al. (Hansen, C.J., Paige, D.A., Young, L.A. [2015]. Icarus 246, 183). Our GCM runs typically span 30 years, from 1985 to 2015, covering the period from the discovery of Pluto's atmosphere to present. For most periods simulated, zonal winds are strongly forced by a gradient wind balance, relaxing in later (recent) years to an angular momentum conservation balance of the seasonal polar cap sublimation flow. Near-surface winds generally follow a sublimation flow from the sunlit polar cap to the polar night cap, with a Coriolis turning of the wind as the air travels from pole to pole. We demonstrate the strong contribution of nitrogen sublimation and deposition to Pluto's atmospheric circulation. As New Horizons data become available, PlutoWRF can be used to construct models of Pluto's atmospheric dynamics and surface wind regimes more constrained by physical observations.
Title: Martian atmospheric collapse: Idealized GCM studies
Authors: Soto, Alejandro; Mischna, Michael; Schneider, Tapio; Lee, Christopher; Richardson, Mark
Affiliation: AA(Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA), AB(Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA), AC(Department of Earth Sciences, ETH Zurich, Switzerland), AD(Ashima Research, Pasadena, CA 91106, USA), AE(Ashima Research, Pasadena, CA 91106, USA)
Journal: Icarus, Volume 250, p. 553-569.
Publication Date: Apr 2015
Keywords: Mars, climate, atmosphere, polar caps, Atmospheres, evolution, dynamics
Abstract Copyright: (c) 2015 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2014.11.028http://bit.ly/1QKB9Hl
Bibliographic Code: 2015Icar..250..553S
Abstract: Global energy balance models of the martian atmosphere predict that, for a range of total CO2 inventories, the CO2 atmosphere may condense until a state with a permanent polar cap is reached. This process, which is commonly referred to as atmospheric collapse, may limit the time available for physical and chemical weathering. The global energy balance models that predict atmospheric collapse represent the climate using simplified parameterizations for atmospheric processes such as radiative transfer and atmospheric heat transport. However, a more detailed representation of these atmospheric processes is critical when the atmosphere is near a transition, such as the threshold for collapse. Therefore, we use the Mars Weather Research and Forecasting (MarsWRF) general circulation model (GCM) to investigate how the explicit representation of meridional heat transport and more detailed radiative transfer affects the onset of atmospheric collapse. Using MarsWRF, we find that previous energy balance modeling underestimates the range of CO2 inventories for which the atmosphere collapses and that the obliquity of Mars determines the range of CO2 inventories that can collapse. For a much larger range of CO2 inventories than expected, atmospheric heat transport is insufficient to prevent the atmospheric collapse. We show that the condensation of CO2 onto Olympus Mons and adjacent mountains generates a condensation flow. This condensation flow syphons energy that would otherwise be transported poleward, which helps explain the large range of CO2 inventories for which the atmosphere collapses.


Title: Feasibility Studies on Guidance and Global Path Planning for Wind-Assisted Montgolfière in Titan
Authors: Fathpour, Nanaz; Blackmore, Lars; Kuwata, Yoshiaki; Assad, Christopher; Wolf, Michael T.; Newman, Claire; Elfes, Alberto; Reh, Kim
Journal: IEEE Systems Journal, vol. 8, issue 4, pp. 1112-1125
Publication Date: Dec 2014
DOI: http://dx.doi.org/10.1109/JSYST.2013.2282700http://bit.ly/1pnplEY
Bibliographic Code: 2014ISysJ...8.1112F
Abstract: Not Available
Title: Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux
Authors: Ayoub, F.; Avouac, J.-P.; Newman, C. E.; Richardson, M. I.; Lucas, A.; Leprince, S.; Bridges, N. T.
Affiliation: AA(Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, MC 100-23, Pasadena, California 91125, USA; fayoub@gps.caltech.edu), AB(), AC(Ashima Research, 600 South Lake Avenue, Suite 104, Pasadena, California 91106, USA), AD(Ashima Research, 600 South Lake Avenue, Suite 104, Pasadena, California 91106, USA), AE(Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, MC 100-23, Pasadena, California 91125, USA), AF(Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, MC 100-23, Pasadena, California 91125, USA), AG(Space Department, 200-W230, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA)
Journal: Nature Communications, Volume 5, id. 5096 (2014).
Publication Date: Sep 2014
Origin: NATURE
Abstract Copyright: (c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI: http://dx.doi.org/10.1038/ncomms6096 http://bit.ly/24AtjKG
Bibliographic Code: 2014NatCo...5E5096A
Abstract: Coupling between surface winds and saltation is a fundamental factor governing geological activity and climate on Mars. Saltation of sand is crucial for both erosion of the surface and dust lifting into the atmosphere. Wind tunnel experiments along with measurements from surface meteorology stations and modelling of wind speeds suggest that winds should only rarely move sand on Mars. However, evidence for currently active dune migration has recently accumulated. Crucially, the frequency of sand-moving events and the implied threshold wind stresses for saltation have remained unknown. Here we present detailed measurements of Nili Patera dune field based on High Resolution Imaging Science Experiment images, demonstrating that sand motion occurs daily throughout much of the year and that the resulting sand flux is strongly seasonal. Analysis of the seasonal sand flux variation suggests an effective threshold for sand motion for application to large-scale model wind fields (1-100 km scale) of τs=0.01±0.0015 N m-2.
Title: Constraints on Mars' recent equatorial wind regimes from layered deposits and comparison with general circulation model results
Authors: Sefton-Nash, E.; Teanby, N. A.; Newman, C.; Clancy, R. A.; Richardson, M. I.
Affiliation: AA(Department of Earth and Space Sciences, University of California Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095, USA), AB(School of Earth Sciences, University of Bristol, Queen's Road, Bristol BS8 1RJ, UK), AC(Ashima Research, 600 S. Lake Ave., Suite 104, Pasadena, CA 91106, USA), AD(School of Earth Sciences, University of Bristol, Queen's Road, Bristol BS8 1RJ, UK), AE(Ashima Research, 600 S. Lake Ave., Suite 104, Pasadena, CA 91106, USA)
Journal: Icarus, Volume 230, p. 81-95.
Publication Date: Feb 2014
Abstract Copyright: (c) 2014 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2013.11.014http://bit.ly/2oM5hQG
Bibliographic Code: 2014Icar..230...81S
Abstract: Aeolian modification has been a fundamental surface process on Mars throughout the Amazonian. Orientations of aeolian features such as bedforms and yardangs are controlled by the prevailing wind regime during the feature's formation. Therefore, observation of recently formed bedform orientations provides a way to probe Mars' recent wind regime and constrain/test general circulation models (GCMs). We collect statistical distributions of transverse bedform and yardang azimuths at nine sites on Mars, and compare measured feature orientations to those predicted by using vector wind field output from the MarsWRF GCM. We focus on layered deposits because their erodible nature makes them applicable to determination of Mars' modern wind regime. Our methods of mapping from the long-term wind field to predicted feature orientations include consideration of wind stress thresholds for sand movement to occur, sand flux equations, and the direction of maximum gross bedform-normal transport. We find that all methods examined typically agree with each other to within ˜15°, though there are some exceptions using high order wind stress weightings with multi-directional annual wind fields. Generally, use of higher wind stress thresholds produces improved matches to bedform orientations. Comparison of multiple yardang orientations to annually variable wind fields is accomplished by inspection of directional maxima in modelled wind vector frequency distributions. Yardangs match well to model predictions and sub-populations in close proximity to each other are shown to match individual directional maxima in GCM output for a single site, implying that topographic effects may produce very localised unidirectional wind fields unresolved by the GCM.