References of "Gérard, Jean-Claude"
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See detailHST Far-Ultraviolet Imaging of Jupiter During the Impacts of Comet Shoemaker-Levy 9
Clarke, John T; Prange, Renee; Ballester, Gilda E et al

in Science (1995), 267

Hubble Space Telescope far-ultraviolet images of Jupiter during the Shoemaker-Levy 9 impacts show the impact regions darkening over the 2 to 3 hours after the impact, becoming darker and more extended ... [more ▼]

Hubble Space Telescope far-ultraviolet images of Jupiter during the Shoemaker-Levy 9 impacts show the impact regions darkening over the 2 to 3 hours after the impact, becoming darker and more extended than at longer wavelengths, which indicates that ultraviolet-absorbing gases or aerosols are more extended, more absorbing, and at higher altitudes than the absorbers of visible light. Transient auroral emissions were observed near the magnetic conjugate point of the K impact site just after that impact. The global auroral activity was fainter than average during the impacts, and a variable auroral emission feature was observed inside the southern auroral oval preceding the impacts of fragments Q1 and Q2. [less ▲]

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See detailThe importance of new chemical sources for the hot oxygen geocorona
Gérard, Jean-Claude ULg; Richards, P. G.; Shematovich, V. I. et al

in Geophysical Research Letters (1995), 22

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2(+) and NO(+) dissociative recombination. The Boltzmann ... [more ▼]

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2(+) and NO(+) dissociative recombination. The Boltzmann equations for thermal and nonthermal populations of O atoms are solved with Monte Carlo stochastic simulation method. It is shown that the calculated energy distribution functions of O atoms are significantly in nonequilibrium in the transition region between the thermosphere and the exosphere. It is found that the inclusion of additional sources leads to stronger disturbances of the energy distribution function and, as a consequence, increases the nonthermal fraction of hot O atoms. The variation of the vertical distribution of hot O between solar maximum and minimum conditions is also evaluated and shows good agreement with the available experimental evidence. [less ▲]

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See detailHubble Space Telescope far-ultraviolet imaging of Jupiter during the impacts of Comet Shoemaker-Levy 9
Clarke, J. T.; Prange, R.; Ballester, G. E. et al

in Highlights of Astronomy, Vol. 10 (1995)

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See detailUltraviolet observations of the Saturnian north aurora and polar haze distribution with the HST-FOC
Gérard, Jean-Claude ULg; Dols, V.; Grodent, Denis ULg et al

in NASA STI/Recon Technical Report N (1995), 96

Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope ... [more ▼]

Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, reveal the presence of an auroral emission near 80 deg N with a peak brightness of about 150 kR of total H2 emission. The maximum optical depth of the polar haze layer is found to be located approximately 5 deg equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H2+ auroral production. In this case, the observed haze optical depth requires an efficiency of aerosol formation of about 6 percent, indicating that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze. [less ▲]

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See detailSpace studies of the upper and middle atmosphere
Gérard, Jean-Claude ULg

in Space scientific research in Belgium (Space Science) (1995)

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See detailCarbon cycle modelling and remote sensing
François, Louis; Gérard, Jean-Claude ULg

in Space scientific research in Belgium (Earth Observations) (1995)

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See detailA new vegetation map and its inclusion in a global biosphere model
Warnant, Pierre ULg; François, Louis ULg; Nemry, Bernard et al

in Guyot (Ed.) Photosynthesis and remote sensing (1995)

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See detailEvolution du Climat et Paléoclimat : effet de serre et CO2
Gérard, Jean-Claude ULg; François, Louis ULg

in Espace et environnement (1995)

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See detailUltraviolet spectroscopy and imaging of planetary atmospheres
Gérard, Jean-Claude ULg

in Space scientific research in Belgium (Space Science) (1995)

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See detailSIMULTANEOUS OBSERVATIONS OF THE SATURNIAN AURORA AND POLAR HAZE WITH THE HST/FOC
Gérard, Jean-Claude ULg; DOLS, V.; Grodent, Denis ULg et al

in Geophysical Research Letters (1995), 22(20), 2685-2688

Near simultaneous observations of the Saturnian H-2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the post-COSTAR Hubble ... [more ▼]

Near simultaneous observations of the Saturnian H-2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the post-COSTAR Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, they reveal the presence of an auroral emission near 80 degrees N with a brightness of about 150 kR of total H-2 emission. The maximum vertical optical depth at 210 nm is found to be located similar to 5 degrees equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H-2(+) auroral production. In this case, the 3 x 10(10) W of H-2 emission observed with the FOG, combined with the deduced haze optical depth requires an efficiency of aerosol formation of about 7%. This result indicates that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze. [less ▲]

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See detailA kinetic model of the formation of the hot oxygen geocorona. 1: Quiet geomagnetic conditions
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by ... [more ▼]

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by chemical processes usually considered as a source of hot oxygen (photodissociation of O2 and dissociative recombination of O2(+) and NO(+) ions). The evolution of the system is described stochastically as a series of random Markovian processes. The energy distribution function of the thermal and non-thermal O(3P) atoms and of the nonthermal O(1D) atoms is calculated from the thermospheric collision-dominated region to the exosphere where the gas flow is virtually collisionless. The model is applied to equatorial latitudes for conditions of low solar and geomagnetic activity. Numerical simulations show that the distribution function of thermal oxygen is increasingly perturbed by collisions with the hot oxygen population at high altitudes and departs significantly from a Maxwellian distribution at all altitudues. The number density and temperature of the nonthermal oxygen atoms are derived from their microscopic distribution function and found tobe in qualitative agreement with previous theoretical and experimental estimates. [less ▲]

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See detailThe morphology of the north Jovian ultraviolet aurora observed with the Hubble Space Telescope
Gérard, Jean-Claude ULg; Dols, Vincent; Prange, Renee et al

in Planetary and Space Science (1994), 42

A series of six images covering a complete rotation of the north polar region of Jupiter were obtained in February 1993 with the Faint Object Camera on board the Hubble Space Telescope (HST). These images ... [more ▼]

A series of six images covering a complete rotation of the north polar region of Jupiter were obtained in February 1993 with the Faint Object Camera on board the Hubble Space Telescope (HST). These images provide the first global picture of the morphology of the Jovian ultraviolet aurora observed from Earth orbit. The camera passband was centered near 153 nm, a region dominated by the H2 Lyman bands and continuum. The successive exposures, taken approximately 90 min apart, are used to construct a polar view of the auroral zone. It is found that the auroral emissions do not exactly follow the footprint of a constant L-shell although the size of the oval and its location agree best with the footprints of the approximately equal to 30 R[SUB]J[/SUB] field line in the GSFC O6 model of the Jovian magnetic field. The displacement between the observed auroral zone and the theoretical oval may indicate a possible distortion of the Jovian magnetic field lines near the surface. A comparison with two images at the same wavelength obtained 8 months earlier shows that the main morphological features are persistent, in spite of changes in the detailed emission distribution. Small scale features with characteristic sizes of approximately 1000 km are observed along the auroral oval. The change of morphology observed as a function of the System 3 longitude appears as a persistent characteristic of the morphology of the north polar aurora. [less ▲]

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See detailTemperature, Ozone, and Nitric Oxide Experiment (TONE) for the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission
Rusch, David W; Barth, Charles A; Clancy, R Todd et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (1994, September 01)

The temperature-ozone-nitric oxide experiment (TONE) on the thermosphere, ionosphere, mesosphere, energetics, and dynamics (TIMED) mission consists of two ultraviolet spectrometers and an infrared ... [more ▼]

The temperature-ozone-nitric oxide experiment (TONE) on the thermosphere, ionosphere, mesosphere, energetics, and dynamics (TIMED) mission consists of two ultraviolet spectrometers and an infrared photometer. A medium resolution spectrometer (MRS) covers the spectral region from 210 to 247 nm with 0.2 nm resolution, and a low resolution spectrometer/infrared photometer (LRS/IRP) covers the 235 to 320 nm region with 2.0 nm resolution, and measures the 1.27 micron emission from molecular oxygen excited by ozone photolysis. The Earth's limb is scanned by articulation mirrors which also serve as the field- of-view limiting elements. The TONE measures profiles of emission as a function of altitude on the Earth's limb. The primary measurements include profiles of Rayleigh scattered sunlight and 1.27 micron emission in the mesosphere and lower thermosphere, and fluorescent emission from nitric oxide in the upper mesosphere and thermosphere. The inverted radiance measurements will yield profiles of temperature, density, and ozone in the mesosphere, and temperature and nitric oxide density in the thermosphere with 2.5 km vertical resolution and 4.5 degree spatial resolution along the orbital path. The primary TONE measurements extend from 50 to 180 km and are fundamental to the science objectives of the TIMED mission. The broad capabilities of the TONE contribute significantly to the TIMED mission with a low-cost, highly reliable instrument based on a long heritage of space instruments built at the University of Colorado's Laboratory for Atmospheric and Space Physics. The TONE has heritage from spectrometers on Mariner 9, Pioneer Venus, the Solar Mesosphere Explorer, Galileo, and Cassini. [less ▲]

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See detailAuroral Lyman alpha and H2 bands from the giant planets: 1. Excitation by proton precipitation in the Jovian atmosphere
Rego, Daniel; Prange, Renee; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman-alpha and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident ... [more ▼]

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman-alpha and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident magnetospheric particle species and energy. The work is planned in three steps: (1) modeling of the volume excitation rate, (2) modeling of the radiative transfer at Lyman-alpha, (3) application to existing observational data and new data obtained from the Hubble Space Telescope. The present paper deals with the first step. Models of the volume excitation rate have previously been developed for low energy electrons and oxygen ions. However, the energy range of the study has to be extended towards higher energy in view of recent results on the penetration depth of the primary particles. Protons have not been modeled so far. We have used an existing electron code of degradation of energy (Gerard and Singh, 1982) which has been improved, updated and adapted to the case of precipitating protons. The issues of nonequilibrium beam H/H(+) fractions and of getting reliable cross sections over a wide energy range have been considered with particular care. The altitude distribution of the volume excitation rate is compared for electrons and protons, for various initial energies in the range 10-50 keV and 50 keV to 1 MeV, respectively. [less ▲]

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See detailHubble Space Telescope Goddard high-resolution spectrograph H2 rotational spectra of Jupiter's aurora
Clarke, John T; Ben Jaffel, Lotfi; Vidal-Madjar, Alfred et al

in Astrophysical Journal (1994), 430

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at ... [more ▼]

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at locations consistent with 6 to 30 R [SUB]J[/SUB] auroral ovals, with much fainter emissions away form the auroral ovals. The emission spectrum is well fitted by both laboratory spectra and theoretical models of optically thin electron excited H2, with added Doppler-broadened Lyman Alpha emission. The observed Lyman Alpha emission wings extend more than 1 A from line center and appear correlated in strength with the H2 brightness. Individual rotational lines in the H2 Werner band system are resolved, allowing a determination of the H2 rotational temperature at the altitude of the emission. We derive best-fit temperatures from 400-450 to 700-750 K, with the auroral emission layer temperature changing either across the auroral oval or over several days' time. These observations demonstrate for the first time the ability to measure the observed rapid H2 temperature variations across Jupiter's auroral atmosphere. [less ▲]

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See detailComparison of IUE and HST diagnostic of the Jovian aurorae
Thomas, Alexandre ULg; Prangé; Ballester, G. E. et al

in Bulletin of the American Astronomical Society (1994, June 01)

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See detailSome Aeronomical Implications of Jupiter's Aurora
Gladstone, G. R.; Waite, J H, Jr; Na, C. Y. et al

in Bulletin of the American Astronomical Society (1994, June 01)

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See detailThe spatial distribution of the UV color ratio of the Jovian aurora observed with the FOC/HST
Grodent, Denis ULg; Gérard, Jean-Claude ULg; Dols, V.

in Bulletin of the American Astronomical Society (1994, June 01)

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See detailAuroral Signature of the Interaction of Comet Shoemaker-Levy 9 with the Jovian Magnetosphere
Prangé; Emerich, C.; Rego, D. et al

in Bulletin of the American Astronomical Society (1994, June 01)

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