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2013

Title: 3D mixing in hot Jupiters atmospheres. I. Application to the day/night cold trap in HD 209458b
Authors: Parmentier, Vivien; Showman, Adam P.; Lian, Yuan
Affiliation: AA(Université de Nice-Sophia Antipolis, Observatoire de la Côte d'Azur, CNRS UMR 6202, BP 4229, 06304, Nice Cedex 4, France vivien.parmentier@oca.eu), AB(Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA), AC(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA, 91106, USA)
Journal: Astronomy & Astrophysics, Volume 558, id.A91, 21 pp.
Publication Date: Oct 2013
Origin: EDP Sciences
Keywords: planets and satellites: atmospheres, methods: numerical, diffusion
DOI: http://dx.doi.org/10.1051/0004-6361/201321132http://bit.ly/2o79oUk
Bibliographic Code: 2013A&A...558A..91P
Abstract: Context. Hot Jupiters exhibit atmospheric temperatures ranging from hundreds to thousands of Kelvin. Because of their large day-night temperature differences, condensable species that are stable in the gas phase on the dayside - such as TiO and silicates - may condense and gravitationally settle on the nightside. Atmospheric circulation may counterbalance this tendency to gravitationally settle. This three-dimensional (3D) mixing of condensable species has not previously been studied for hot Jupiters, yet it is crucial to assess the existence and distribution of TiO and silicates in the atmospheres of these planets. Aims: We investigate the strength of the nightside cold trap in hot Jupiters atmospheres by investigating the mechanisms and strength of the vertical mixing in these stably stratified atmospheres. We apply our model to the particular case of TiO to address the question of whether TiO can exist at low pressure in sufficient abundances to produce stratospheric thermal inversions despite the nightside cold trap. Methods: We modeled the 3D circulation of HD 209458b including passive (i.e. radiatively inactive) tracers that advect with the 3D flow, with a source and sink term on the nightside to represent their condensation into haze particles and their gravitational settling. Results: We show that global advection patterns produce strong vertical mixing that can keep condensable species aloft as long as they are trapped in particles of sizes of a few microns or less on the nightside. We show that vertical mixing results not from small-scale convection but from the large-scale circulation driven by the day-night heating contrast. Although this vertical mixing is not diffusive in any rigorous sense, a comparison of our results with idealized diffusion models allows a rough estimate of the effective vertical eddy diffusivities in these atmospheres. The parametrization Kzz=5 × 104/ Pbar m2s-1, valid from ~1 bar to a few μbar, can be used in 1D models of HD 209458b. Moreover, our models exhibit strong spatial and temporal variability in the tracer concentration that could result in observable variations during either transit or secondary eclipse measurements. Finally, we apply our model to the case of TiO in HD 209458b and show that the day-night cold trap would deplete TiO if it condenses into particles bigger than a few microns on the planet's nightside, keeping it from creating the observed stratosphere of the planet. Appendix A is available in electronic form at http://www.aanda.org
Title: Growth and form of the mound in Gale Crater, Mars: Slope wind enhanced erosion and transport
Authors: Kite, Edwin S.; Lewis, Kevin W.; Lamb, Michael P.; Newman, Claire E.; Richardson, Mark I.
Affiliation: AA(California Institute of Technology), AB(Princeton University), AC(California Institute of Technology), AE(Ashima Research)
Journal: Geology, vol. 41, p. 543-546
Publication Date: May 2013
Origin: AUTHOR
DOI: http://dx.doi.org/10.1130/G33909.1http://bit.ly/1aPTnD1
Bibliographic Code: 2013Geo....41..543K
Abstract: Ancient sediments provide archives of climate and habitability on Mars. Gale Crater, the landing site for the Mars Science Laboratory (MSL), hosts a 5-km-high sedimentary mound (Mount Sharp/Aeolis Mons). Hypotheses for mound formation include evaporitic, lacustrine, fluviodeltaic, and aeolian processes, but the origin and original extent of Gale’s mound is unknown. Here we show new measurements of sedimentary strata within the mound that indicate ˜3° outward dips oriented radially away from the mound center, inconsistent with the first three hypotheses. Moreover, although mounds are widely considered to be erosional remnants of a once crater-filling unit, we find that the Gale mound’s current form is close to its maximal extent. Instead we propose that the mound’s structure, stratigraphy, and current shape can be explained by growth in place near the center of the crater mediated by wind-topography feedbacks. Our model shows how sediment can initially accrete near the crater center far from crater-wall katabatic winds, until the increasing relief of the resulting mound generates mound-flank slope winds strong enough to erode the mound. The slope wind enhanced erosion and transport (SWEET) hypothesis indicates mound formation dominantly by aeolian deposition with limited organic carbon preservation potential, and a relatively limited role for lacustrine and fluvial activity. Morphodynamic feedbacks between wind and topography are widely applicable to a range of sedimentary and ice mounds across the Martian surface, and possibly other planets.
Title: The impact of a realistic vertical dust distribution on the simulation of the Martian General Circulation
Authors: Guzewich, Scott D.; Toigo, Anthony D.; Richardson, Mark I.; Newman, Claire E.; Talaat, Elsayed R.; Waugh, Darryn W.; McConnochie, Timothy H.
Affiliation: AA(NASA Goddard Spaceflight Center, Greenbelt, Maryland USA), AB(The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland USA), AC(Ashima Research, Pasadena, California USA), AD(Ashima Research, Pasadena, California USA), AE(The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland USA), AF(Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland USA), AG(Department of Astronomy, University of Maryland, College Park, Maryland USA)
Journal: Journal of Geophysical Research: Planets, Volume 118, Issue 5, pp. 980-993
Publication Date: May 2013
Origin: WILEY
Keywords: Mars Atmosphere, Dust, GCM Modeling
Abstract Copyright: ©2013. American Geophysical Union. All Rights Reserved.
DOI: http://dx.doi.org/10.1002/jgre.20084http://bit.ly/1ncyr61
Bibliographic Code: 2013JGRE..118..980G
Abstract: Limb-scanning observations with the Mars Climate Sounder and Thermal Emission Spectrometer (TES) have identified discrete layers of enhanced dust opacity well above the boundary layer and a mean vertical structure of dust opacity very different from the expectation of well-mixed dust in the lowest 1-2 scale heights. To assess the impact of this vertical dust opacity profile on atmospheric properties, we developed a TES limb-scan observation-based three-dimensional and time-evolving dust climatology for use in forcing general circulation models (GCMs). We use this to force the MarsWRF GCM and compare with simulations that use a well-mixed (Conrath-ν) vertical dust profile and Mars Climate Database version 4 (MCD) horizontal distribution dust opacity forcing function. We find that simulated temperatures using the TES-derived forcing yield a 1.18 standard deviation closer match to TES temperature retrievals than a MarsWRF simulation using MCD forcing. The climatological forcing yields significant changes to many large-scale features of the simulated atmosphere. Notably the high-latitude westerly jet speeds are 10-20 m/s higher, polar warming collar temperatures are 20-30 K warmer near northern winter solstice and tilted more strongly poleward, the middle and lower atmospheric meridional circulations are partially decoupled, the migrating diurnal tide exhibits destructive interference and is weakened by 50% outside of equinox, and the southern hemisphere wave number 1 stationary wave is strengthened by up to 4 K (45%). We find the vertical dust distribution is an important factor for Martian lower and middle atmospheric thermal structure and circulation that cannot be neglected in analysis and simulation of the Martian atmosphere.
Title: Zonal wavenumber three traveling waves in the northern hemisphere of Mars simulated with a general circulation model
Authors: Wang, Huiqun; Richardson, Mark I.; Toigo, Anthony D.; Newman, Claire E.
Affiliation: AA(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA), AB(Ashima Research, Pasadena, CA 91101, USA), AC(Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA), AD(Ashima Research, Pasadena, CA 91101, USA)
Journal: Icarus, Volume 223, Issue 2, p. 654-676.
Publication Date: Apr 2013
Origin: ELSEVIER
Abstract Copyright: Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2013.01.004http://bit.ly/12XkM2Q
Bibliographic Code: 2013Icar..223..654W
Abstract: Observations suggest a strong correlation between curvilinear shaped traveling dust storms (observed in wide angle camera images) and eastward traveling zonal wave number m = 3 waves (observed in thermal data) in the northern mid and high latitudes during the fall and winter. Using the MarsWRF General Circulation Model, we have investigated the seasonality, structure and dynamics of the simulated m = 3 traveling waves and tested the hypothesis that traveling dust storms may enhance m = 3 traveling waves under certain conditions.Our standard simulation using a prescribed "MGS dust scenario" can capture the observed major wave modes and strong near surface temperature variations before and after the northern winter solstice. The same seasonal pattern is also shown by the simulated near surface meridional wind, but not by the normalized surface pressure. The simulated eastward traveling 1.4 < T < 10 sol m = 3 waves are confined near the surface in terms of the temperature perturbation, EP flux and eddy available potential energy, and they extend higher in terms of the eddy winds and eddy kinetic energy. The signature of the simulated m = 3 traveling waves is stronger in the near surface meridional wind than in the near surface temperature field.Compared with the standard simulation, our test simulations show that the prescribed m = 3 traveling dust blobs can enhance the simulated m = 3 traveling waves during the pre- and post-solstice periods when traveling dust storms are frequently observed in images, and that they have negligible effect during the northern winter solstice period when traveling dust storms are absent. The enhancement is even greater in our simulation when dust is concentrated closer to the surface. Our simulations also suggest that dust within the 45-75°N band is most effective at enhancing the simulated m = 3 traveling waves.There are multiple factors influencing the strength of the simulated m = 3 traveling waves. Among those, our study suggests that weaker near surface static stability, larger near surface baroclinic parameter, and wave-form dust forcing for latitudinally extended dust storms are favorable. Further study is needed to fully understand the importance of these factors and others.
Title: Effects of obliquity and water vapor/trace gas greenhouses in the early martian climate
Authors: Mischna, Michael A.; Baker, Victor; Milliken, Ralph; Richardson, Mark; Lee, Christopher
Affiliation: AA(Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California USA), AB(Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona USA), AC(Department of Geological Sciences, Brown University, Providence, Rhode Island USA), AD(Ashima Research, Pasadena, California USA), AE(Ashima Research, Pasadena, California USA)
Journal: Journal of Geophysical Research: Planets, Volume 118, Issue 3, pp. 560-576
Publication Date: Mar 2013
Origin: WILEY
Keywords: early Mars, sulfur, volcanism, obliquity, greenhouse effect, MarsWRF
Abstract Copyright: ©2013. American Geophysical Union. All Rights Reserved.
DOI: http://dx.doi.org/10.1002/jgre.20054http://bit.ly/1plx6LD
Bibliographic Code: 2013JGRE..118..560M
Abstract: We explore possible mechanisms for the generation of warm, wet climates on early Mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions. The presence of both water vapor (a strong greenhouse gas) and other trace greenhouse gases (such as SO2) in a predominantly CO2 atmosphere may act, under certain conditions, to elevate surface temperatures above the freezing point of liquid water, at least episodically. Variations in obliquity are explored to investigate whether these periodic variations in insolation at Mars can broaden the regions or seasons where warm temperatures can exist. We use the Mars Weather Research and Forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by Johnson et al. (2008). While achieving temperatures above 273 K globally remains challenging, the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions, which can help to explain the presence of fluvial surface features (e.g., valley networks) and hydrous minerals of post-Noachian age, a period when alternate methods do not convincingly explain the sustainability of liquid water. Furthermore, we find that global warming can be achieved with the presence of a darker surface globally, which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea.
Title: Compositional effects in Titan's thermospheric gravity waves
Authors: Cui, J.; Lian, Y.; Müller-Wodarg, I. C. F.
Affiliation: AA(School of Astronomy and Space Sciences, Nanjing University, Nanjing, China), AB(Department of Physics, Imperial College, London, UK), AC(Department of Physics, Imperial College, London, UK)
Journal: Geophysical Research Letters, Volume 40, Issue 1, pp. 43-47
Publication Date: Jan 2013
Origin: WILEY
Abstract Copyright: >©2013. American Geophysical Union. All Rights Reserved
DOI: http://dx.doi.org/10.1029/2012GL054621http://bit.ly/13uNjgV
Bibliographic Code: 2013GeoRL..40...43C
Abstract: In Titan's upper atmosphere, the density profiles of several constituents (N2, CH4, H2, and 29N2) as measured by the Cassini Ion Neutral Mass Spectrometer show periodical structures which we interpret as internal gravity waves. Compositional effects are frequently seen in the data, in which the wave structures in different constituents show different amplitudes and phase angles. We use a simple linearized wave perturbation theory to explain the observations, emphasizing their role as a useful diagnostic of the basic wave parameters. For the T39 flyby, the data-model comparison constrains typical wavelength to be ~150-500 km, typical wave period from the Brunt-Väisälä period of ~62 min up to ~6 h. Our calculations also illustrate that wave-induced diffusion is important for CH4 and H2.

2012

Title: Angular momentum conservation in a simplified Venus General Circulation Model
Authors: Lee, C.; Richardson, M. I.
Affiliation: AA(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91101, USA), AB(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91101, USA)
Journal: Icarus, Volume 221, Issue 2, p. 1173-1176.
Publication Date: Nov 2012
Origin: ELSEVIER
Abstract Copyright: (c) 2012 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2012.10.007http://bit.ly/1105n1B
Bibliographic Code: 2012Icar..221.1173L
Abstract: Angular momentum (AM) conservation and transport are critical components of all General Circulation Model (GCM) simulations, and particularly for simulations of the Venus atmosphere. We show that a Venus GCM based upon the Geophysical Fluid Dynamics Laboratory (GFDL) Flexible Modeling System (FMS) GCM conserves angular momentum to better than 2% per 1000 Venus years (≈225,000 Earth days) of integration under the extreme conditions of a simplified Venus simulation with low surface torques. With no topography in the GCM, physical torques due to surface/atmosphere frictional interactions dominate the acceleration of an initially stationary atmosphere and provide more than four times the angular momentum of solid body co-rotation over an integration period of 100 Venus years. During the subsequent steady state period of 200 Venus years negligible mean physical torques cause variation in the total angular momentum of less than 5% and produce a stable multi-century simulation. Diffusion and damping processes within the GCM account for AM losses of less than 0.2% per 1000 Venus years. This study provides a stable comparison point for other GCMs by employing a simplified forcing scheme. The diagnostics and analysis require little or no modification to the core GCM and are sufficiently robust to allow easy model inter-comparison.
Title: Development of a fast, accurate radiative transfer model for the Martian atmosphere, past and present
Authors: Mischna, Michael A.; Lee, Christopher; Richardson, Mark
Affiliation: AA(Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA), AB(Ashima Research, Pasadena, California, USA), AC(Ashima Research, Pasadena, California, USA)
Journal: Journal of Geophysical Research, Volume 117, Issue E10, CiteID E10009
Publication Date: Oct 2012
Origin: AGU
Keywords: Atmospheric Composition and Structure: Planetary atmospheres (5210, 5405, 5704), Planetary Sciences: Astrobiology: Planetary atmospheres, clouds, and hazes (0343), Planetary Sciences: Solid Surface Planets: Atmospheres (0343, 1060)
Abstract Copyright: (c) 2012: American Geophysical Union
DOI: http://dx.doi.org/10.1029/2012JE004110http://bit.ly/W82l7h
Bibliographic Code: 2012JGRE..11710009M
Abstract: We present details of an approach to creating a k-distribution radiative transfer model (KDM) for use in the Martian atmosphere. Such models preserve the accuracy of more rigorous line-by-line models, but are orders of magnitude faster, and can be effectively implemented in 3-D general circulation models. The approach taken here is sufficiently generalized that it can be employed for atmospheres of any arbitrary composition and mass, and demonstrations are provided for simulated atmospheres with a present-day Martian surface pressure (∼6 mb) and a putative thick early Mars atmosphere (∼500 mb), both with and without atmospheric water vapor. KDM-derived absorption coefficients are placed into a look-up table at a set of gridded points in pressure, temperature and atmospheric composition, and a tri-linear interpolation scheme is used to obtain the coefficients appropriate for the local atmospheric conditions. These coefficients may then be used within any of a variety of commonly used flux solvers to obtain atmospheric heating rates. A series of validation tests are performed with the KDM for both present-day and early Mars atmospheric conditions, and the model is compared against several other widely used radiative transfer schemes, including several used in contemporary general circulation models. These validation results identify weaknesses in some other approaches and demonstrate the efficacy of the KDM, providing a rigorous test of these types of models for use in the Martian atmosphere. A demonstration of results obtained by implementing the KDM in a Mars general circulation model is provided.
Title: REMS: The Environmental Sensor Suite for the Mars Science Laboratory Rover
Authors: Gómez-Elvira, J.; Armiens, C.; Castañer, L.; Domínguez, M.; Genzer, M.; Gómez, F.; Haberle, R.; Harri, A.-M.; Jiménez, V.; Kahanpää, H.; Kowalski, L.; Lepinette, A.; Martín, J.; Martínez-Frías, J.; McEwan, I.; Mora, L.; Moreno, J.; Navarro, S.; de Pablo, M. A.; Peinado, V.; Peña, A.; Polkko, J.; Ramos, M.; Renno, N. O.; Ricart, J.; Richardson, M.; Rodríguez-Manfredi, J.; Romeral, J.; Sebastián, E.; Serrano, J.; de la Torre Juárez, M.; Torres, J.; Torrero, F.; Urquí, R.; Vázquez, L.; Velasco, T.; Verdasca, J.; Zorzano, M.-P.; Martín-Torres, J.
Affiliation: AA(Centro de Astrobiología (CSIC-INTA)), AB(Centro de Astrobiología (CSIC-INTA)), AC(Universidad Politécnica de Cataluña), AD(Universidad Politécnica de Cataluña), AE(FMI), AF(Centro de Astrobiología (CSIC-INTA)), AG(NASA Ames Research Center), AH(FMI), AI(Universidad Politécnica de Cataluña), AJ(FMI), AK(Universidad Politécnica de Cataluña), AL(Centro de Astrobiología (CSIC-INTA)), AM(Centro de Astrobiología (CSIC-INTA)), AN(Centro de Astrobiología (CSIC-INTA)), AO(Ashima Research), AP(Centro de Astrobiología (CSIC-INTA)), AQ(EADS-CRISA), AR(Centro de Astrobiología (CSIC-INTA)), AS(Universidad de Alcalá de Henares), AT(Centro de Astrobiología (CSIC-INTA)), AU(EADS-CRISA), AV(FMI), AW(Universidad de Alcalá de Henares), AX(Michigan University), AY(Universidad Politécnica de Cataluña), AZ(Ashima Research), BA(Centro de Astrobiología (CSIC-INTA)), BB(Centro de Astrobiología (CSIC-INTA)), BC(Centro de Astrobiología (CSIC-INTA)), BD(EADS-CRISA! ), BE(Jet Propulsion Laboratory), BF(Centro de Astrobiología (CSIC-INTA)), BG(EADS-CRISA), BH(INSA), BI(Universidad Complutence de Madrid), BJ(EADS-CRISA), BK(Centro de Astrobiología (CSIC-INTA)), BL(Centro de Astrobiología (CSIC-INTA)), BM(Centro de Astrobiología (CSIC-INTA))
Journal: Space Science Reviews, Volume 170, Issue 1-4, pp. 583-640
Publication Date: Sep 2012
Origin: SPRINGER
Keywords: Mars, Mars Science Laboratory, Atmosphere, Meteorology, Pressure, Relative Humidity, Wind, Ultraviolet radiation, Temperature
Abstract Copyright: (c) 2012: Springer Science+Business Media B.V.
DOI: http://dx.doi.org/10.1007/s11214-012-9921-1http://bit.ly/W82nvV
Bibliographic Code: 2012SSRv..170..583G
Abstract: The Rover Environmental Monitoring Station (REMS) will investigate environmental factors directly tied to current habitability at the Martian surface during the Mars Science Laboratory (MSL) mission. Three major habitability factors are addressed by REMS: the thermal environment, ultraviolet irradiation, and water cycling. The thermal environment is determined by a mixture of processes, chief amongst these being the meteorological. Accordingly, the REMS sensors have been designed to record air and ground temperatures, pressure, relative humidity, wind speed in the horizontal and vertical directions, as well as ultraviolet radiation in different bands. These sensors are distributed over the rover in four places: two booms located on the MSL Remote Sensing Mast, the ultraviolet sensor on the rover deck, and the pressure sensor inside the rover body. Typical daily REMS observations will collect 180 minutes of data from all sensors simultaneously (arranged in 5 minute hourly samples plus 60 additional minutes taken at times to be decided during the course of the mission). REMS will add significantly to the environmental record collected by prior missions through the range of simultaneous observations including water vapor; the ability to take measurements routinely through the night; the intended minimum of one Martian year of observations; and the first measurement of surface UV irradiation. In this paper, we describe the scientific potential of REMS measurements and describe in detail the sensors that constitute REMS and the calibration procedures.
Title: The impact of resolution on the dynamics of the martian global atmosphere: Varying resolution studies with the MarsWRF GCM
Authors: Toigo, Anthony D.; Lee, Christopher; Newman, Claire E.; Richardson, Mark I.
Affiliation: AA(The Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA), AB(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA), AC(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA), AD(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA)
Journal: Icarus, Volume 221, Issue 1, p. 276–288.
Publication Date: Aug 2012
Origin: ELSEVIER
Abstract Copyright: Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2012.07.020http://bit.ly/PUT9VM
Bibliographic Code: 2012Icar..218.1043L
Abstract: We investigate the sensitivity of the circulation and thermal structure of the martian atmosphere to numerical model resolution in a general circulation model (GCM) using the martian implementation (MarsWRF) of the planetWRF atmospheric model. We provide a description of the MarsWRF GCM and use it to study the global atmosphere at horizontal resolutions from 7.5  9 to 0.5  0.5, encompassing the range from standard Mars GCMs to global mesoscale modeling. We find that while most of the gross-scale features of the circulation (the rough location of jets, the qualitative thermal structure, and the major large-scale features of the surface level winds) are insensitive to horizontal resolution over this range, several major features of the circulation are sensitive in detail. The northern winter polar circulation shows the greatest sensitivity, showing a continuous transition from a smooth polar winter jet at low resolution, to a distinct vertically ‘‘split’’ jet as resolution increases. The separation of the lower and middle atmosphere polar jet occurs at roughly 10 Pa, with the split jet structure developing in concert with the intensification of meridional jets at roughly 10 Pa and above 0.1 Pa. These meridional jets appear to represent the separation of lower and middle atmosphere mean overturning circulations (with the former being consistent with the usual concept of the ‘‘Hadley cell’’). Further, the transition in polar jet structure is more sensitive to changes in zonal than meridional horizontal resolution, suggesting that representation of small-scale wave-mean flow interactions is more important than fine-scale representation of the meridional thermal gradient across the polar front. Increasing the horizontal resolution improves the match between the modeled thermal structure and the Mars Climate Sounder retrievals for northern winter high latitudes. While increased horizontal resolution also improves the simulation of the northern high latitudes at equinox, even the lowest model resolution considered here appears to do a good job for the southern winter and southern equinoctial pole (although in detail some discrepancies remain). These results suggest that studies of the northern winter jet (e.g., transient waves and cyclogenesis) will be more sensitive to global model resolution that those of the south (e.g., the confining dynamics of the southern polar vortex relevant to studies of argon transport). For surface winds, the major effect of increased horizontal resolution is in the superposition of circulations forced by local-scale topography upon the large-scale surface wind patterns. While passive predictions of dust lifting are generally insensitive to model horizontal resolution when no lifting threshold is considered, increasing the stress threshold produces significantly more lifting in higher resolution simulations with the generation of finer-scale, higher-stress winds due primarily to better-resolved topography. Considering the positive feedbacks expected for radiatively active dust lifting, we expect this bias to increase when such feedbacks are permitted.
Title: The Ashima/MIT Mars GCM and argon in the martian atmosphere
Authors: Lian, Yuan; Richardson, Mark I.; Newman, Claire E.; Lee, Christopher; Toigo, Anthony D.; Mischna, Michael A.; Campin, Jean-Michel
Affiliation: AA(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA), AB(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA), AC(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA), AD(Ashima Research, Suite 104, 600 South Lake Ave., Pasadena, CA 91106, USA), AE(The Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA), AF(Jet Propulsion Laboratory, M/S 183-601, 4800 Oak Grove Drive, Pasadena, CA 91109, USA), AG(Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 54-1424, 77 Massachusetts Ave., Cambridge, MA 02139-4307, USA)
Journal: Icarus, Volume 218, Issue 2, p. 1043-1070.
Publication Date: Apr 2012
Origin: ELSEVIER
Abstract Copyright: (c) 2012 Elsevier Inc.
DOI: http://dx.doi.org/10.1016/j.icarus.2012.02.012http://bit.ly/Ykn6Cd
Bibliographic Code: 2012Icar..218.1043L
Abstract: We investigate the ability of modern general circulation models (GCMs) to simulate transport in the martian atmosphere using measurements of argon as a proxy for the transport processes. Argon provides the simplest measure of transport as it is a noble gas with no sinks or sources on seasonal timescales. Variations in argon result solely from 'freeze distillation', as the atmosphere condenses at the winter poles, and from atmospheric transport. Comparison of all previously published models when rescaled to a common definition of the argon enhancement factor (EF) suggest that models generally do a poor job in predicting the peak enhancement in southern winter over the winter pole - the time when the capability of the model transport approaches are most severely tested. Despite observed peak EF values of ˜6, previously published model predictions peaked at EF values of only 2-3. We introduce a new GCM that provides a better treatment of mass conservation within the dynamical core, includes more sophisticated tracer transport approaches, and utilizes a cube-sphere grid structure thus avoiding the grid-point convergence problem at the pole that exists for most current Mars GCMs. We describe this model - the Ashima Research/Massachusetts Institute of Technology Mars General Circulation Model (Ashima/MIT Mars GCM) and use it to demonstrate the significant sensitivity of peak EF to the choices of transport approach for both tracers and heat. We obtain a peak EF of 4.75 which, while over 50% higher than any prior model, remains well short of the observed value. We show that the polar EF value in winter is primarily determined by the competition between two processes: (1) mean meridional import of lower-latitude air not enriched in argon and (2) the leakage of enriched argon out of the polar column by eddies in the lowest atmospheric levels. We suggest possibilities for improving GCM representation of the CO2 cycle and the general circulation that may further improve the simulation of the argon cycle. We conclude that current GCMs may be insufficient for detailed simulation of transport-sensitive problems like the water cycle and potentially also the dust cycle.
Title: Winds and tides of Ligeia Mare, with application to the drift of the proposed time TiME (Titan Mare Explorer) capsule
Authors: Lorenz, Ralph D.; Tokano, Tetsuya; Newman, Claire E.
Affiliation: AA(JHU Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA), AB(Institut für Geophysik und Meteorologie, Universität zu Köln, Albertus-Magnus-Platz, 50923 Köln, Germany), AC(Ashima Research, 600 S. Lake Avenue Suite 104, Pasadena, CA 91106, USA)
Journal: Planetary and Space Science, Volume 60, Issue 1, p. 72-85.
Publication Date: Jan 2012
Origin: ELSEVIER
Abstract Copyright: (c) 2012 Elsevier Ltd
DOI: http://dx.doi.org/10.1016/j.pss.2010.12.009http://bit.ly/1TQXbh1
Bibliographic Code: 2012P&SS...60...72L
Abstract: We use two independent General Circulation Models (GCMs) to estimate surface winds at Titan’s Ligeia Mare (78° N, 250° W), motivated by a proposed mission to land a floating capsule in this ∼500 km hydrocarbon sea. The models agree on the overall magnitude (∼0.5-1 m/s) and seasonal variation (strongest in summer) of windspeeds, but details of seasonal and diurnal variation of windspeed and direction differ somewhat, with the role of surface exchanges being more significant than that of gravitational tides in the atmosphere. We also investigate the tidal dynamics in the sea using a numerical ocean dynamics model: assuming a rigid lithosphere, the tidal amplitude is up to ∼0.8 m. Tidal currents are overall proportional to the reciprocal of depth-with an assumed central depth of 300 m, the characteristic tidal currents are ∼1 cm/s, with notable motions being a slosh between Ligeia’s eastern and western lobes, and a clockwise flow pattern. We find that a capsule will drift at approximately one tenth of the windspeed, unless measures are adopted to augment the drag areas above or below the waterline. Thus motion of a floating capsule is dominated by the wind, and is likely to be several km per Earth day, a rate that will be readily measured from Earth by radio navigation methods. In some instances, the wind vector rotates diurnally such that the drift trajectory is epicyclic.