The respective roles of surface temperature driven feedbacks and tropospheric adjustment to CO2 in CMIP5 transient climate simulations     

Lorenzo Tomassini  Olivier Geoffroy  Jean-Louis Dufresne  Abderrahmane Idelkadi  Chiara Cagnazzo  Karoline Block  Thorsten Mauritsen  Marco Giorgetta  Johannes Quaas 《Climate Dynamics》2013,41(11-12):3103-3126

An overview of radiative climate feedbacks and ocean heat uptake efficiency diagnosed from idealized transient climate change experiments of 14 CMIP5 models is presented. Feedbacks explain about two times more variance in transient climate response across the models than ocean heat uptake efficiency. Cloud feedbacks can clearly be identified as the main source of inter-model spread. Models with strong longwave feedbacks in the tropics feature substantial increases in cloud ice around the tropopause suggestive of changes in cloud-top heights. The lifting of the tropical tropopause goes together with a general weakening of the tropical circulation. Distinctive inter-model differences in cloud shortwave feedbacks occur in the subtropics including the equatorward flanks of the storm-tracks. Related cloud fraction changes are not confined to low clouds but comprise middle level clouds as well. A reduction in relative humidity through the lower and mid troposphere can be identified as being the main associated large-scale feature. Experiments with prescribed sea surface temperatures are analyzed in order to investigate whether the diagnosed feedbacks from the transient climate simulations contain a tropospheric adjustment component that is not conveyed through the surface temperature response. The strengths of the climate feedbacks computed from atmosphere-only experiments with prescribed increases in sea surface temperatures, but fixed CO₂ concentrations, are close to the ones derived from the transient experiment. Only the cloud shortwave feedback exhibits discernible differences which, however, can not unequivocally be attributed to tropospheric adjustment to CO₂. Although for some models a tropospheric adjustment component is present in the global mean shortwave cloud feedback, an analysis of spatial patterns does not lend support to the view that cloud feedbacks are dominated by their tropospheric adjustment part. Nevertheless, there is positive correlation between the strength of tropospheric adjustment processes and cloud feedbacks across different climate models.  相似文献   

An empirical model for transient crater growth in granular targets based on direct observations     

Satoru Yamamoto  Olivier S. Barnouin-Jha  Seiji Sugita 《Icarus》2009,203(1):310-319

The present paper describes observations of crater growth up to the time of transient crater formation and presents a new empirical model for transient crater growth as a function of time. Polycarbonate projectiles were impacted vertically into soda-lime glass sphere targets using a single-stage light-gas gun. Using a new technique with a laser sheet illuminating the target [Barnouin-Jha, O.S., Yamamoto, S., Toriumi, T., Sugita, S., Matsui, T., 2007. Non-intrusive measurements of the crater growth. Icarus, 188, 506-521], we measured the temporal change in diameter of crater cavities (diameter growth). The rate of increase in diameter at early times follows a power law relation, but the data at later times (before the end of transient crater formation) deviates from the power law relation. In addition, the power law exponent at early times and the degree of deviation from a power law at later times depend on the target. In order to interpret these features, we proposed to modify Maxwell’s Z-model under the assumption that the strength of the excavation flow field decreases exponentially with time. We also derived a diameter growth model as: d(t)∝[1-exp(-βt)]^γ, where d(t) is the apparent diameter of the crater cavity at time t after impact, and β and γ are constants. We demonstrated that the diameter growth model could represent well the experimental data for various targets with different target material properties, such as porosity or angle of repose. We also investigated the diameter growth for a dry sand target, which has been used to formulate previous scaling relations. The obtained results showed that the dry sand target has larger degree of deviation from a power law, indicating that the target material properties of the dry sand target have a significant effect on diameter growth, especially at later times. This may suggest that the previously reported scaling relations should be reexamined in order to account for the late-stage behavior with the effect of target material properties.  相似文献   

Water sorption on martian regolith analogs: Thermodynamics and near-infrared reflectance spectroscopy     

Antoine Pommerol  Bernard Schmitt  Pierre Beck  Olivier Brissaud 《Icarus》2009,204(1):114-136

The near-infrared reflectance spectra of the martian surface present strong absorption features attributed to hydration water present in the regolith. In order to characterize the relationships between this water and atmospheric vapor and decipher the physical state of water molecules in martian regolith analogs, we designed and built an experimental setup to measure near-IR reflectance spectra under martian atmospheric conditions. Six samples were studied that cover part of the diversity of Mars surface mineralogy: a hydrated ferric oxide (ferrihydrite), two igneous samples (volcanic tuff, and dunite sand), and three potential water rich soil materials (Mg-sulfate, smectite powder and a palagonitic soil, the JSC Mars-1 regolith stimulant). Sorption and desorption isotherms were measured at 243 K for water vapor pressure varying from 10⁻⁵ to ∼0.3 mbar (relative humidity: 10⁻⁴ to 75%). These measurements reveal a large diversity of behavior among the sample suite in terms of absolute amount of water adsorbed, shape of the isotherm and hysteresis between the adsorption and desorption branches. Simultaneous in situ spectroscopic observations permit a detailed analysis of the spectral signature of adsorbed water and also point to clear differences between the samples. Ferric (oxy)hydroxides like ferrihydrite or other phases present in palagonitic soils are very strong water adsorbent and may play an important role in the current martian water cycle by allowing large exchange of water between dust-covered regions and atmosphere at diurnal and seasonal scales.  相似文献   

A survey of possible impact structures on 25143 Itokawa     

Naru Hirata  Olivier S. Barnouin-Jha  Chikatoshi Honda  Ryosuke Nakamura  Hideaki Miyamoto  Sho Sasaki  Hirohide Demura  Akiko M. Nakamura  Tatsuhiro Michikami  Robert W. Gaskell  Jun Saito 《Icarus》2009,200(2):486-502

We determined the morphologies and dimensions of possible impact craters on the surface of Asteroid 25143 Itokawa from images taken by the Hayabusa spacecraft. Circular depressions, circular features with flat floors or convex floors, and circular features with smooth surfaces were identified as possible craters. The survey identified 38 candidates with widely varying morphologies including rough, smooth and saddle-shaped floors, a lack of raised rims and fresh material exposures. The average depth/diameter ratio was 0.08±0.03: these craters are very shallow relative to craters observed on other asteroids. These shallow craters are a result of (1) target curvature influencing the cratering process, (2) raised rim not being generated by this process, and (3) fines infilling the craters. As many of the crater candidates have an unusual appearance, we used a classification scheme that reflects the likelihood of an observed candidate's formation by a hypervelocity impact. We considered a variety of alternative interpretations while developing this scheme, including inherited features from a proto-Itokawa, spall scars created by the disruption of the proto-Itokawa, spall scars following the formation of a large crater on Itokawa itself, and apparent depressions due to random arrangements of boulders. The size-frequency distribution of the crater candidates was close to the empirical saturation line at the largest diameter, and then decline with decreasing diameter.  相似文献   

Lander radioscience for obtaining the rotation and orientation of Mars     

Veronique Dehant  William Folkner  Etienne Renotte  Daniel Orban  Sami Asmar  Georges Balmino  Jean-Pierre Barriot  Jeremy Benoist  Richard Biancale  Jens Biele  Frank Budnik  Stefaan Burger  Olivier de Viron  Bernd Häusler  Özgur Karatekin  Sébastien Le Maistre  Philippe Lognonné  Michel Menvielle  Michel Mitrovic  Martin Pätzold  Marie Yseboodt 《Planetary and Space Science》2009,57(8-9):1050-1067

The paper presents the concept, the objectives, the approach used, and the expected performances and accuracies of a radioscience experiment based on a radio link between the Earth and the surface of Mars. This experiment involves radioscience equipment installed on a lander at the surface of Mars. The experiment with the generic name lander radioscience (LaRa) consists of an X-band transponder that has been designed to obtain, over at least one Martian year, two-way Doppler measurements from the radio link between the ExoMars lander and the Earth (ExoMars is an ESA mission to Mars due to launch in 2013). These Doppler measurements will be used to obtain Mars’ orientation in space and rotation (precession and nutations, and length-of-day variations). More specifically, the relative position of the lander on the surface of Mars with respect to the Earth ground stations allows reconstructing Mars’ time varying orientation and rotation in space.Precession will be determined with an accuracy better by a factor of 4 (better than the 0.1% level) with respect to the present-day accuracy after only a few months at the Martian surface. This precession determination will, in turn, improve the determination of the moment of inertia of the whole planet (mantle plus core) and the radius of the core: for a specific interior composition or even for a range of possible compositions, the core radius is expected to be determined with a precision decreasing to a few tens of kilometers.A fairly precise measurement of variations in the orientation of Mars’ spin axis will enable, in addition to the determination of the moment of inertia of the core, an even better determination of the size of the core via the core resonance in the nutation amplitudes. When the core is liquid, the free core nutation (FCN) resonance induces a change in the nutation amplitudes, with respect to their values for a solid planet, at the percent level in the large semi-annual prograde nutation amplitude and even more (a few percent, a few tens of percent or more, depending on the FCN period) for the retrograde ter-annual nutation amplitude. The resonance amplification depends on the size, moment of inertia, and flattening of the core. For a large core, the amplification can be very large, ensuring the detection of the FCN, and determination of the core moment of inertia.The measurement of variations in Mars’ rotation also determines variations of the angular momentum due to seasonal mass transfer between the atmosphere and ice caps. Observations even for a short period of 180 days at the surface of Mars will decrease the uncertainty by a factor of two with respect to the present knowledge of these quantities (at the 10% level).The ultimate objectives of the proposed experiment are to obtain information on Mars’ interior and on the sublimation/condensation of CO₂ in Mars’ atmosphere. Improved knowledge of the interior will help us to better understand the formation and evolution of Mars. Improved knowledge of the CO₂ sublimation/condensation cycle will enable better understanding of the circulation and dynamics of Mars’ atmosphere.  相似文献   

Post-starburst galaxies: more than just an interesting curiosity     

Vivienne Wild  C. Jakob Walcher  Peter H. Johansson  Laurence Tresse  Stéphane Charlot  Agnieszka Pollo  Olivier Le Fèvre  Loic de Ravel 《Monthly notices of the Royal Astronomical Society》2009,395(1):144-159

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TNOs are Cool: A Survey of the Transneptunian Region     

Thomas G. Müller  Emmanuel Lellouch  Hermann Böhnhardt  John Stansberry  Antonella Barucci  Jacques Crovisier  Audrey Delsanti  Alain Doressoundiram  Elisabetta Dotto  René Duffard  Sonia Fornasier  Olivier Groussin  Pedro J. Gutiérrez  Olivier Hainaut  Alan W. Harris  Paul Hartogh  Daniel Hestroffer  Jonathan Horner  Dave Jewitt  Mark Kidger  Csaba Kiss  Pedro Lacerda  Luisa Lara  Tanya Lim  Michael Mueller  Raphael Moreno  Jose-Luis Ortiz  Miriam Rengel  Pablo Santos-Sanz  Bruce Swinyard  Nicolas Thomas  Audrey Thirouin  David Trilling 《Earth, Moon, and Planets》2009,105(2-4):209-219

Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well.  相似文献   

Influence of shallow infiltration on time-lapse ERT: Experience of advanced interpretation   总被引：1，自引：0，他引：1  

Rémi Clément  Marc Descloitres  Thomas Günther  Olivier Ribolzi  Anatoli Legchenko 《Comptes Rendus Geoscience》2009,341(10-11):886-898

Previous time-lapse Electrical Resistivity Tomography (ERT) studies have experienced difficulties in reconstructing reliable calculated resistivity changes in the subsurface. Increases or decreases of resistivity appear in the calculated ERT image where no changes were noted in the subsurface, leading to erroneous hydrological interpretations of the geophysical results. In this article, we investigate how a variation of actual resistivity with time and at shallow depth can influence time-lapse ERT results and produce resistivity artefacts at depth. We use 1 and 2-D numerical modelling to simulate infiltration scenarios. Using a standard time-lapse inversion, we demonstrate the resistivity artefact production according to the electrode spacing parameter. We used an advanced inversion methodology with a decoupling line at shallow depth to attenuate or remove resistivity artefacts. We also applied this methodology to a field data set obtained in a semi-arid environment in Burkina Faso, West Africa. Here, time-lapse ERT shows several resistivity artefacts of calculated resistivity if a standard inversion is used. We demonstrate the importance of a dense sampling of shallow resistivity variations at shallow depth. Advanced interpretation allows us to significantly attenuate or remove the resistivity artefact production at intermediate depth and produce reliable interpretation of hydrological processes.  相似文献   

Constraints from deuterium on the formation of icy bodies in the Jovian system and beyond     

Jonathan Horner  Olivier Mousis  Jonathan I. Lunine 《Planetary and Space Science》2008,56(12):1585-1595

We consider the role of deuterium as a potential marker of location and ambient conditions during the formation of small bodies in our Solar system. We concentrate in particular on the formation of the regular icy satellites of Jupiter and the other giant planets, but include a discussion of the implications for the Trojan asteroids and the irregular satellites. We examine in detail the formation of regular planetary satellites within the paradigm of a circum-Jovian subnebula. Particular attention is paid to the two extreme potential subnebulae—“hot” and “cold”. In particular, we show that, for the case of the “hot” subnebula model, the D:H ratio in water ice measured from the regular satellites would be expected to be near-Solar. In contrast, satellites which formed in a “cold” subnebula would be expected to display a D:H ratio that is distinctly over-Solar. We then compare the results obtained with the enrichment regimes which could be expected for other families of icy small bodies in the outer Solar system—the Trojan asteroids and the irregular satellites. In doing so, we demonstrate how measurements by Laplace, the James Webb Space Telescope, HERSCHEL and ALMA will play an important role in determining the true formation locations and mechanisms of these objects.  相似文献   

S₂O, polysulfuroxide and sulfur polymer on Io's surface?     

Donia Baklouti  Bernard Schmitt  Olivier Brissaud 《Icarus》2008,194(2):647-659

To settle the question of disulfur monoxide and sulfur monoxide deposition and occurrence on Io's surface, we performed series of laboratory experiments reproducing the condensation of S₂O at low temperature. Its polymerization has been monitored by recording infrared spectra under conditions of temperature, pressure, mixing with SO₂ and UV-visible radiation simulating that of Io's surface. Our experiments show that S₂O condensates are not chemically stable under ionian conditions. We also demonstrate that SO and S₂O outgassed by Io's volcanoes and condensing on Io's surface should lead to yellow polysulfuroxide deposits or to white deposits of S₂O diluted in sulfur dioxide frost (i.e., S₂O/SO₂ < 0.1%). Thus S₂O condensation cannot be responsible for the red volcanic deposits on Io. Comparison of the laboratory infrared spectra of S₂O and polysulfuroxide with NIMS/Galileo infrared spectra of Io's surface leads us to discuss the possible identification of polysulfuroxide. We also recorded the visible transmission spectra of sulfur samples resulting from polysulfuroxide decomposition. These samples consist in a mixture of sulfur polymer and orthorhombic sulfur. Using the optical constants extracted from these measurements, we show that a linear combination of the reflectance spectra of our samples, the reflectance spectrum of orthorhombic S₈ sulfur and SO₂ reflectance spectrum, leads to a very good matching of Io's visible spectrum between 330 and 520 nm. We conclude then that Io's surface is probably mainly composed of sulfur dioxide and a mixture of sulfur S₈ and sulfur polymer. Some polysulfuroxide could also co-exist with these dominant components, but is probably restricted to some volcanic areas.  相似文献