266 results on '"Fouchet, Thierry"'
Search Results
252. A far wing lineshape for H2 broadened CH4 infrared transitions
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Hartmann, Jean-Michel, primary, Boulet, Christian, additional, Brodbeck, Claude, additional, van Thanh, Nguyen, additional, Fouchet, Thierry, additional, and Drossart, Pierre, additional
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- 2002
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253. Meridional distribution of CH3C2H and C4H2 in Saturn’s stratosphere from CIRS/Cassini limb and nadir observations
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Guerlet, Sandrine, Fouchet, Thierry, Bézard, Bruno, Moses, Julianne I., Fletcher, Leigh N., Simon-Miller, Amy A., and Michael Flasar, F.
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MERIDIONAL winds , *STRATOSPHERE , *INFRARED spectroscopy , *ACETYLENE , *CHEMICAL reactions , *HYDROCARBONS , *SATURN (Planet) - Abstract
Abstract: Limb and nadir spectra acquired by Cassini/CIRS (Composite InfraRed Spectrometer) are analyzed in order to derive, for the first time, the meridional variations of diacetylene (C4H2) and methylacetylene (CH3C2H) mixing ratios in Saturn’s stratosphere, from 5hPa up to 0.05hPa and 80°S to 45°N. We find that the C4H2 and CH3C2H meridional distributions mimic that of acetylene (C2H2), exhibiting small-scale variations that are not present in photochemical model predictions. The most striking feature of the meridional distribution of both molecules is an asymmetry between mid-southern and mid-northern latitudes. The mid-southern latitudes are found depleted in hydrocarbons relative to their northern counterparts. In contrast, photochemical models predict similar abundances at north and south mid-latitudes. We favor a dynamical explanation for this asymmetry, with upwelling in the south and downwelling in the north, the latter coinciding with the region undergoing ring shadowing. The depletion in hydrocarbons at mid-southern latitudes could also result from chemical reactions with oxygen-bearing molecules. Poleward of 60°S, at 0.1 and 0.05hPa, we find that the CH3C2H and C4H2 abundances increase dramatically. This behavior is in sharp contradiction with photochemical model predictions, which exhibit a strong decrease towards the south pole. Several processes could explain our observations, such as subsidence, a large vertical eddy diffusion coefficient at high altitudes, auroral chemistry that enhances CH3C2H and C4H2 production, or shielding from photolysis by aerosols or molecules produced from auroral chemistry. However, problems remain with all these hypotheses, including the lack of similar behavior at lower altitudes. Our derived mean mixing ratios at 0.5hPa of (2.4±0.3)×10−10 for C4H2 and of (1.1±0.3)×10−9 for CH3C2H are compatible with the analysis of global-average ISO observations performed by Moses et al. (Moses, J.I., Bézard, B., Lellouch, E., Gladstone, G.R., Feuchtgruber, H., Allen, M. [2000a]. Icarus 143, 244–298). Finally, we provide values for the ratios [CH3C2H]/[C2H2] and [C4H2]/[C2H2] that can constrain the coupled chemistry of these hydrocarbons. [Copyright &y& Elsevier]
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- 2010
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254. Search for spatial variation in the jovian 15N/14N ratio from Cassini/CIRS observations
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Fouchet, Thierry, Irwin, Patrick G.J., Parrish, Paul, Calcutt, Simon B., Taylor, Frederic W., Nixon, Conor A., and Owen, Tobias
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ATMOSPHERE of Jupiter , *SPECTROMETERS , *SPACE vehicles , *NITROGEN - Abstract
We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the 15N/14N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that 15NH3 is not fractionated in Jupiter''s atmosphere, and that the measured 15N/14N represents Jupiter''s global value. Our mean value for the global jovian 15N/14N ratio of
(2.22±0.52)×10-3 agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223–243) and Owen et al. (2001, Astrophys. J. 553, L77–L79). We argue that the jovian isotopic 15N/14N ratio must represent the solar nitrogen isotopic composition. The solar 15N/14N ratio hence significantly differs from the terrestrial value: (15N/14N)⊕=3.68×10-3 . This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown. [Copyright &y& Elsevier]- Published
- 2004
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255. ISO-SWS Observations of Jupiter: Measurement of the Ammonia Tropospheric Profile and of the 15N/14N Isotopic Ratio
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Fouchet, Thierry, Lellouch, Emmanuel, Be´zard, Bruno, Encrenaz, The´re`se, Drossart, Pierre, Feuchtgruber, Helmut, and de Graauw, Thijs
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We present the results of the Infrared Space Observatory Short Wavelength Spectrometer (ISO-SWS) observations of Jupiter related to ammonia. We focus on two spectral regions; the first one (the 10-μm region), ranging from 9.5 to 11.5 μm, probes atmospheric levels between 1 and 0.2 bar, while the second one (the 5-μm window), ranging from 4.8 to 5.5 μm, sounds the atmosphere between 8 and 2 bar. The two spectral windows cannot be fitted with the same ammonia vertical distribution. From the 10-μm region we infer an ammonia distribution of about half the saturation profile above the 1-bar level, where the N/H ratio is roughly solar. A totally different picture is derived from the 5-μm window, where we determine an upper limit of 3.7×10−5 at 1 bar and find an increasing NH3 abundance at least down to 4 bar. This profile is similar to that measured by the Galileo probe. The discrepancy between the two spectral regions most likely arises from the spatial heterogeneity of Jupiter, the 5-μm window sounding dry areas unveiled by a locally thin cloud cover (the 5-μm hot spots), and the 10-μm region probing the mean jovian atmosphere above 1 bar. The 15NH3 mixing ratio is measured around 400 mbar from ν2 band absorptions in the 10-μm region. We find the atmosphere of Jupiter highly depleted in 15N at this pressure level [(15N/14N)[formula]=1.9+0.9−1.0)×10−3, while (15N/14N)⊕=3.68×10−3]. It is not clear whether this depletion reveals the global jovian 15N/14N ratio. Instead an isotopic fractionation process, taking place during the ammonia cloud condensation, is indicated as a possible mechanism. A fractionation coefficient α higher than 1.08 would explain the observed isotopic ratio, but the lack of laboratory data does not allow us to decide unambiguously on the origin of the observed low 15N/14N ratio.
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- 2000
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256. Mapping of Jupiter's tropospheric NH3 abundance using ground-based IRTF/TEXES observations at 5 μm.
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Blain, Doriann, Fouchet, Thierry, Greathouse, Thomas, Encrenaz, Thérèse, Charnay, Benjamin, Bézard, Bruno, Li, Cheng, Fletcher, Leigh, Lellouch, Emmanuel, Orton, Glenn, and Drossart, Pierre
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ATMOSPHERIC circulation , *TROPOSPHERIC chemistry , *RADIATIVE transfer , *SPECTROGRAPHS , *CUBES , *TELESCOPES - Abstract
We report on results of an observational campaign to support the Juno mission. At thebeginning of 2016, using TEXES (Texas Echelon cross-dispersed Echelle Spectrograph),mounted on the NASA Infrared Telescope Facility (IRTF), we obtained data cubes ofJupiter in the 1930–1943 cm−1 (5.14 - 5.18 μm) spectral range, which probes theatmosphere in the 1–4 bar region, with a spectral resolution of ≈ 0.15 cm −1 and anangular resolution of ≈ 1.4′′. This dataset is analyzed by a code which combines aline-by-line radiative transfer model with a non-linear optimal estimation inversionmethod. The inversion retrieves the vertical abundance profiles of NH3 — which is themain contributor at these wavelengths — with a maximum sensitivity at ≈ 1–3bar, as well as the cloud transmittance. This retrieval is performed on more thanone thousand pixels of our data cubes, producing maps of the disk, where all themajor belts are visible. We will discuss the results presented in our article, namelyour retrieved NH3 abundance maps which can be compared with the distributionobserved by Juno’s MWR (Bolton et al. 2017, Li et al. 2017) in the 2 bar regionand their significance for the understanding of Jupiter’s atmospheric dynamics. [ABSTRACT FROM AUTHOR]
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- 2019
257. HDO and SO2 thermal mapping on Venus : Statistical analysis of the SO2 plumes.
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Widemann, Thomas, Encrenaz, Thérèse, Greathouse, Thomas, Marcq, Emmanuel, Sagawa, Hideo, Bézard, Bruno, Fouchet, Thierry, Lefèvre, Franck, Lebonnois, Sébastien, Atreya, Sushil, Lee, Yeon Joo, Giles, Rohini, and Watanabe, Shigeto
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- 2019
258. Ground-based infrared mapping of H2O2 on Mars near opposition.
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Encrenaz, Therese, Geathouse, Thomas, Aoki, Shohei, Daerden, Frank, Giuranna, Marco, Lefèvre, Franck, Montmessin, Franck, Forget, François, Fouchet, Thierry, Bézard, Bruno, Atreya, Sushil, DeWitt, Curtis, Richter, Matthew, Neary, Lori, and Viscardy, Sébastien
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- 2019
259. Monitoring the thermal structure and minor species of Venus mesosphere with ALMA submm observations
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Arianna Piccialli, Moreno, Raphael, Encrenaz, Therese A., Fouchet, Thierry, Lellouch, Emmanuel, Moullet, Arielle, Widemann, Thomas, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Planétologie du LESIA, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)
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[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
International audience
260. Global Climate Modeling of Saturn's troposphere and stratosphere, with applications to Jupiter
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Spiga, Aymeric, Lebonnois, Sébastien, Fouchet, Thierry, Millour, Ehouarn, Guerlet, Sandrine, Cabanes, Simon, Boissinot, Alexandre, Dubos, Thomas, Leconte, J., Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF), Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS), ECLIPSE 2018, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École des Ponts ParisTech (ENPC)-École polytechnique (X)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), and Pomies, Marie-Paule
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Physics::Space Physics ,[SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,[SDU.ASTR.EP] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,Astrophysics::Earth and Planetary Astrophysics ,Physics::Atmospheric and Oceanic Physics - Abstract
International audience; The Cassini mission has opened many science questions related to Saturn's atmospheric dynamics: jet-streams (including the hexagonal-shaped northern polar jet), giant convective storms, stratospheric equatorial oscillations, interhemispheric transport. This inspired our group to develop a Global Climate Model for Saturn that couples a massively-parallel icosahedral-grid hydrodynamical solver with detailed physical parameterizations (notably correlated-k radiative transfer) for Saturn's troposphere and stratosphere. Multiple test simulations led us to determine the best modeling settings to run simulations in which (amongst other requirements) the conservation of angular momentum is ensured with good accuracy. Multi-year simulations carried out with a spatial resolution of 1/2° in latitude/longitude allowed us to analyze the mechanisms accounting for jet acceleration (and possible latitudinal migration) in the troposphere and the stratosphere of Saturn, the formation of large-scale vortices and waves, and the occurrence of a zonostrophic regime. The perspectives for improvements of the reference Saturn simulations will be reviewed. We will also present simulations carried out for Jupiter (presently observed by the Juno mission) with the exact same modeling platform, to discuss comparative dynamics between both gas giants.
261. In situ Exploration of the Giant Planets
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Mousis, Olivier, Atkinson, David H., Ambrosi, Richard, Atreya, Sushil, Banfield, Don, Barabash, Stas, Blanc, Michel, Cavalié, Thibault, Coustenis, Athena, Deleuil, Magali, Durry, Georges, Ferri, Francesca, Fletcher, Leigh, Fouchet, Thierry, Guillot, Tristan, Hartogh, Paul, Hueso, Ricardo, Hofstadter, Mark, Lebreton, Jean-Pierre, Mandt, Kathleen E., Rauer, Heike, Rannou, Pascal, Renard, Jean-Baptiste, Sanchez-Lávega, Agustin, Sayanagi, Kunio, Simon, Amy, Spilker, Thomas, Venkatapathy, Ethiraj, Waite, J. Hunter, and Wurz, Peter
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13. Climate action ,520 Astronomy ,620 Engineering ,7. Clean energy - Abstract
Remote sensing observations suffer significant limitations when used to study the bulk atmospheric compositionof the giant planets of our solar system. This impacts our knowledge of the formation of these planets andthe physics of their atmospheres. A remarkable example of the superiority of in situ probe measurements wasillustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases’abundances and the precise measurement of the helium mixing ratio were only made available through in situmeasurements by the Galileo probe. Here we describe the main scientific goals to be addressed by the futurein situ exploration of Saturn, Uranus, and Neptune, placing the Galileo probe exploration of Jupiter in a broadercontext. An atmospheric entry probe targeting the 10-bar level would yield insight into two broad themes: i) theformation history of the giant planets and that of the Solar System, and ii) the processes at play in planetaryatmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, withdata returned to Earth using a Carrier Relay Spacecraft as a relay station. An atmospheric probe could representa significant ESA contribution to a future NASA New Frontiers or flagship mission to be launched toward Saturn,Uranus, and/or Neptune.
262. HDO and SO2 thermal mapping on Venus: Statistical analysis of the SO2 plumes and comparison with space data.
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Encrenaz, Therese, Greathouse, Thomas, Marcq, Emmanuel, Sagawa, Hideo, Widemann, Thomas, Bezard, Bruno, Fouchet, Thierry, Atreya, Sushil, and Yeon Joo Lee
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- 2018
263. Vertical abundance profiles of hydrocarbons in Titan's atmosphere at 15° S and 80° N retrieved from Cassini/CIRS spectra
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Vinatier, Sandrine, Bézard, Bruno, Fouchet, Thierry, Teanby, Nick A., de Kok, Remco, Irwin, Patrick G.J., Conrath, Barney J., Nixon, Conor A., Romani, Paul N., Flasar, F. Michael, and Coustenis, Athena
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STRATOSPHERE , *SPECTRUM analysis , *CHEMOSPHERE , *UPPER atmosphere - Abstract
Abstract: Limb spectra recorded by the Composite InfraRed Spectrometer (CIRS) on Cassini provide information on abundance vertical profiles of C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C6H6 and HCN, along with the temperature profiles in Titan''s atmosphere. We analyzed two sets of spectra, one at 15° S (Tb flyby) and the other one at 80° N (T3 flyby). The spectral range 600–1400 cm−1, recorded at a resolution of 0.5 cm−1, was used to determine molecular abundances and temperatures in the stratosphere in the altitude range 100–460 km for Tb and 170–495 km for T3. Both temperature profiles show a well defined stratopause, at around 310 km (0.07 mbar) and 183 K at 13° S, and 380 km (0.01 mbar) with 207 K at 80° N. Near the north pole, stratospheric temperatures are colder and mesospheric temperatures are warmer than near the equator. C2H2, C2H6, C3H8 and HCN display vertical mixing ratio profiles that increase with height at 15° S and 80° N, consistent with their formation in the upper atmosphere, diffusion downwards and condensation in the lower stratosphere, as expected from photochemical models. The CH3C2H and C4H2 mixing ratios also increase with height at 15° S. But near the north pole, their profiles present an unexpected minimum around 300 km, observed for the first time thanks to the high vertical resolution of the CIRS limb data. C2H4 is the only molecule having a vertical abundance profile that decreases with height at 15° S. At 80° N, it also displays a minimum of its mixing ratio around the 0.1-mbar level. For C6H6, an upper limit of 1.1 ppb (in the 0.3–10 mbar range) is derived at 15° S, whereas a constant mixing ratio profile of is inferred near the north pole. At 15° S, the vertical profile of HCN exhibits a steeper gradient than other molecules, which suggests that a sink for this molecule exists in the stratosphere, possibly due to haze formation. All molecules display a more or less pronounced enrichment towards the north pole, probably due, in part, to subsidence of air at the north (winter) pole that brings air enriched in photochemical compounds from the upper atmosphere to lower levels. [Copyright &y& Elsevier]
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- 2007
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264. First atmospheric results produced by the SuperCam instrument on Mars2020
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Franck Montmessin, Timothy McConnochie, Thierry Fouchet, Olivier Forni, Paolo Pilleri, Clément Royer, Elise Knutsen, Tanguy Bertrand, Olivier Gasnault, Jeremie Lasue, Carey Legett, Mark Lemmon, Raymond Newell, Dawn Venhaus, Sylvestre Maurice, Roger Wiens, and Fouchet, Thierry
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[SDU.ASTR.EP] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] - Abstract
The SuperCam instrument [1,2] onboard Mars2020 disposes of a variety of active and passive techniques, including passive spectroscopy in the 0.40-0.85 (VIS) and 1.3 to 2.6 microns (IR, [3,4]) wavelength ranges. Since the landing on Mars of Perseverance in February 2021, Supercam has acquired numerous observations of its near and distant environment, exploring the geological and mineralogical context of Jezero crater. In addition, several measurements were devoted to probing the atmosphere surrounding the Perseverance rover. The technique of using sky spectra in passive mode, known as "passive sky", has already been demonstrated with ChemCam on the Mars Science Laboratory (MSL) rover [4]. SuperCam provides a superset of the ChemCam capabilities used in [4], and in particular adds a near-infrared component that includes absorption and scattering characteristics of key gases and aerosols/clouds. "Passive sky" measurements have typically been performed every other week to allow a consistent monitoring of the seasonal evolution of the main quantities (CO2, O2, H2O, CO, aerosols/clouds). Particular attention was given to joint measurements of O2 and CO, as they appear as key components of the Martian chemical cycle and have never been measured together at the same time on the surface of Mars. As the 2 m wavelength region is used for the first time at the surface of Mars, it enables the detection of CO (around 2.35 m). CO possesses a small absorption that has made it difficult to identify in SuperCam spectra so far. An overview of SuperCam's progress to date in its attempt to characterize the Martian atmosphere at Jezero will be presented. References : [1] Wiens, R.C., et al. , 2021. Space Sci Rev 217, 4, [2] Maurice, S., et al., 2021. Space Sci Rev 217, 47, [3] Royer, C., et al.., 2020. Review of Scientific Instruments 91, 063105, [4] Fouchet, T., et al., 2021, Icarus, submitted. [5] McConnochie T. H et al., 2018. Icarus 307, 294
- Published
- 2021
265. Seasonal photochemical modeling of Jupiter and Saturn’s stratosphere
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Hue, Vincent, STAR, ABES, Dobrijevic, Michel, Lellouch, Emmanuel, Spiga, Aymeric, Hersant, Franck, Cavalie, Thibaut, Greathouse, Thomas, Loison, Jean-Christophe, Fouchet, Thierry, Michel Dobrijevic, Jean-Christophe Loison [Président], Thierry Fouchet [Rapporteur], Emmanuel Lellouch, Aymeric Spiga, Franck Hersant, Thibaut Cavalie, Thomas Greathouse, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Université de Bordeaux
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Simulations ,Thermal structure ,Photochemistry ,Evolution ,Transfert radiatif ,Chemical composition ,Réseau chimique réduit ,Planètes géantes ,Cassini-Huygens ,[SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph] ,Giant Planets ,Dynamique atmosphérique ,Couplage température- chimie ,Numerical modeling ,Photochemical model ,Radiative transfer ,Modèle photochimique ,Stratosphère ,Atmospheric dynamics ,Stratosphere ,[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph] ,2D-model ,Saturne ,Photochimie ,Temperature-chemistry feedback ,Composition chimique ,Radiative model ,Chemical network ,Saturn ,Seasonal effects ,Jupiter ,Reduced chemical network ,Effets saisonniers ,Modèle radiatif ,Structure thermique ,Réseau chimique ,Simulations numériques - Abstract
One of the goals of this thesis is to interpret the observations of the main hydrocarbons(C2H2 and C2H6) from Cassini (NASA/ESA) on Jupiter and Saturn. The one-dimensional photochemical models are insufficient to explain these spatially resolved observations. I have developed the first two-dimensional (altitude-latitude) seasonal photochemical model for the giant planets, which predicts their chemical composition.Without meridional transport, Saturn’s chemical composition follows the insolation variations. The C2H2 and C2H6 abundances measured by Cassini (Guerlet et al., 2009)are reproduced from the equator up to mid-latitudes, at pressures higher than 0.1mbar.At higher latitudes, the disagreements suggest either a stratospheric circulation cell orthe signature of ion-neutral chemistry. For the first time, I have coupled our seasonal photochemical model with the seasonal radiative model of Greathouse et al. (2008). I predict that the seasonal temperature peak is shifted half a season earlier, with respect to previous models, at high latitudes in the higher stratosphere.Jupiter shows weak seasonal variations of chemical composition, only controlled by its orbital eccentricity. The observed meridional distributions of C2H2 and C2H6 show opposition trends (Nixon et al., 2010). C2H6 observed distribution is reproduced when Isuppose a combination of meridional diffusion and stratospheric circulation, while causingat the same time a stronger agreement with the C2H2 observations. Accounting for theion-neutral chemistry might preferentially affect C2H2 and potentially play a key role on hydrocarbon abundances in Jupiter’s stratosphere., L’un des objectifs de cette thèse est d’interpréter les observations des principaux hydrocarbures(C2H2 et C2H6) effectuées par Cassini (NASA/ESA) sur Jupiter et Saturne. Les modèles photochimiques à une dimension sont insuffisants pour interpréter ces observations spatialement résolues. J’ai développé le premier modèle photochimique saisonnier à deux dimensions (altitude-latitude) des planètes géantes qui calcule leur composition chimique.En l’absence de transport méridional, la composition chimique de Saturne suit les variations d’ensoleillement. Les abondances de C2H2 et C2H6 mesurées par Cassini (Guerletet al., 2009) sont reproduites jusqu’aux latitudes moyennes, à des pressions supérieures à0,1mbar. Les écarts notés dans l’hémisphère sud suggèrent la présence de dynamique ou d’une chimie entre les ions et les espèces neutres. J’ai couplé, pour la première fois, mon modèle photochimique avec le modèle radiatif de Greathouse et al. (2008). Nous prédisons un décalage du pic saisonnier de température, par rapport aux précédents modèles, d’une demi-saison à haute altitude et aux hautes latitudes.Jupiter présente de faibles variations saisonnières de composition chimique, uniquement contrôlées par son excentricité. Les distributions méridionales observées de C2H2 etC2H6 présentent des tendances opposées (Nixon et al., 2010). Mon modèle est en accord avec les observations de C2H6 lorsque j’invoque une combinaison de diffusion méridionale et de circulation stratosphérique, tout en provoquant un plus grand désaccord avec les observations de C2H2. La chimie ionique pourrait principalement affecter C2H2 et jouer un rôle important dans l’atmosphère de Jupiter.
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- 2015
266. Température et composition de la stratosphère de Saturne à partir des données Cassini/CIRS
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Guerlet, Sandrine, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Paris, and Fouchet, Thierry
- Subjects
astronomy ,Télédétection ,Spectroscopie infrarouge ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,Saturne (planète) ,Sondes spatiales - Abstract
The goal of the thesis is to measure the temperature and composition fields in Saturn's stratosphere. In order to do so, we analyze spectra of the thermal emission of the planet acquired in limb geometry by CIRS, an infrared spectrometer aboard the Cassini spacecraft. These spectral signatures are analyzed using a radiative transfer model coupled to a retrieval algorithm in order to measure vertical profiles of the temperature and of the abundance of atmospheric gases. We have thus obtained the first maps, from 70N to 80 S, and on several scale heights, of the temperature and abundance of five hydrocarbons. The temperature map we obtain is used to quantify the thermal response of the atmosphere to seasonal variations in isolation. We compare the gradients we measure to the radiative seasonal model of Greathouse et al. [2008]. We also report the discovery of an equatorial oscillation in temperature and zonal wind proles in the stratosphere of Saturn, similar to the Earth's quasi-biennial oscillation, and we present its temporal evolution between 2005 and 2010. This analysis of the hydrocarbon's distributions and their comparaison to a seasonal photochemical model [Moses and Greathouse, 2005] shows signs of meridional transport in the lower stratosphere, from the equator to the poles, and vertical transport in the upper stratosphere. Finally, we present a detailed analysis of the radiative exhanges in the stratosphere using the Net Exhange Rates formulation. This work will form the basis for a future parameterization of radiative transfer computation, a necessary step in developing a general circulation model of Saturn's stratosphere.; L'objectif de cette thèse est de mesurer les champs de température et de composition de la stratosphère de Saturne. Pour cela, j'ai analysé des spectres de l'émission thermique de la planète acquis au limbe par CIRS, un spectromètre infrarouge à bord de la sonde Cassini. L'analyse de ces signatures spectrales à l'aide d'un code de transfert de rayonnement et d'une méthode d'inversion permet de mesurer les profils verticaux de la température et de l'abondance des constituants. J'ai ainsi réalisé les premières cartographies, de 70°N à 80°S et sur plusieurs échelles de hauteur, de la température et de l'abondance de 5 hydrocarbures. La carte de température obtenue permet de quantifier la réponse de l'atmosphère aux variations saisonnières de l'ensoleillement. Les gradients mesurés sont comparés au modèle radiatif saisonnier de Greathouse et la. [2008]. Je montre la découverte d'une oscillation équatoriale de température et de vent zonal dans la stratosphère de Saturne, analogue à l'oscillation quasi-biennale terrestre, et je présente son évolutioin entre 2005 et 2010. L'analyse de la distribution des hydrocarbures et la comparaison à un modèle de photochimie saisonnier [Moses and greathouse, 2005] met en évidence des indices de transport méridien dans la basse stratosphère. Enfin, je présente un travail d'analyse des échanges radiatifs dans la stratosphère, de l'équateur vers les pôles, et de transport vertical dans la haute stratosphère à l'aide d'une formulation en puissances nettes échangées. Ce travail servira de base à une future paramétrisation du transfert de rayonnement, étape nécessaire au développement d'un modèle de circulation générale de la stratosphère de Saturne.
- Published
- 2010
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