References of "Gérard, Jean-Claude"
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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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See detailA REMARKABLE AURORAL EVENT ON JUPITER OBSERVED IN THE ULTRAVIOLET WITH THE HUBBLE-SPACE-TELESCOPE
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Prangé, R. et al

in Science (1994), 266(5191), 1675-1678

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete are in near corotation ... [more ▼]

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete are in near corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of similar to 1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete are had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae. [less ▲]

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See detailHST-FOC observations of a remarkable UV auroral event on Jupiter
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Prangé, R. et al

in NASA STI/Recon Technical Report N (1994), 95

Two sets of UV (ultraviolet) images of the Jovian north aurora were obtained with the Faint Object Camera (FOC) on Hubble. The first series shows a very intense discrete arc in corotation with the planet ... [more ▼]

Two sets of UV (ultraviolet) images of the Jovian north aurora were obtained with the Faint Object Camera (FOC) on Hubble. The first series shows a very intense discrete arc in corotation with the planet. The maximum apparent H2 emission rate corresponds to an electron precipitation of approximately 1/sq Wm, a very large flux in comparison with the solar EUV (extreme ultraviolet) heating. The hugh particle heating rate of the auroral upper atmosphere of Jupiter is expected to cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours later, the discrete arc had considerably decreased in brightness. The timescale and magnitude of the change in the UV aurora strongly suggests that the discrete Jovian auroral precipitation is related to large scale current system variations as are the Earth's discrete aurorae. [less ▲]

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

in Space scientific research in Belgium, Vol. III, Earth Observation, Part 2 (1994)

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See detailCARAIB - A global model of terrestrial biological productivity
Warnant, Pierre ULg; François, Louis ULg; Strivay, David ULg et al

in Global Biogeochemical Cycles (1994), 8(3), 255-270

CARAIB, a mechanistic model of carbon assimilation in the biosphere estimates the net primary productivity (NPP) of the continental vegetation on a grid of 1 degrees x 1 degrees in latitude and longitude ... [more ▼]

CARAIB, a mechanistic model of carbon assimilation in the biosphere estimates the net primary productivity (NPP) of the continental vegetation on a grid of 1 degrees x 1 degrees in latitude and longitude. The model considers the annual and diurnal cycles. It is based on the coupling of the three following submodels; a leaf assimilation model including estimates of stomatal conductance and leaf respiration, a canopy model describing principally the radiative transfer through the foliage, and a wood respiration model. Present-day climate and vegetation characteristics allow the discrimination between ecotypes. In particular, specific information on vegetation distribution and properties is successfully used at four levels; the leaf physiological level, the plant level, the ecosystem level, and the global level. The productivity determined by the CARAIB model is compared with local measurements and empirical estimates showing a good agreement with a global value of 65 Gt C yr(-1). The sensitivity of the model to the diurnal cycle and to the abundance of C-4 species is also tested. The productivity slightly decreases (10%) when the diurnal cycle of the temperature is neglected. By contrast, neglecting the diurnal cycle of solar irradiance produces unrealistically high values of NPP. Even if the importance of this increase would presumably be reduced by the coupling of CARAIB with a nutrient cycle model, this test emphasizes the key role of the diurnal cycle in a mechanistic model of the NPP. Uncertainties on the abundance and spatial distribution of C-4 plants may cause errors in the NPP estimates, however, as demonstrated by two sensitivity tests, these errors are certainly lower than 10% at the global scale as shown by two tests. [less ▲]

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See detailSuperthermal particules in planetary atmospheres
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Non-stable processes in the Univers (1994)

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See detailHIGH-RESOLUTION SPECTRA OF JUPITER NORTHERN AURORAL ULTRAVIOLET EMISSION WITH THE HUBBLE-SPACE-TELESCOPE
TRAFTON, L. M.; Gérard, Jean-Claude ULg; Munhoven, Guy ULg et al

in Astrophysical Journal (1994), 421(2), 816-827

The first spectroscopic observations of planetary aurora with the HST are reported. These include spectral regions centered on the H-2 Lyman and Werner bands of a region of Jupiter's northern aurora. The ... [more ▼]

The first spectroscopic observations of planetary aurora with the HST are reported. These include spectral regions centered on the H-2 Lyman and Werner bands of a region of Jupiter's northern aurora. The observations were made with the Goddard High Resolution Spectrograph (GHRS) using the Large Science Aperture as part of a campaign to study Jupiter at the time of the Ulysses flyby. The individual rotational-vibrational bands are resolved and the observed emissions are essentially all from H-2. A rotational-vibrational temperature for H-2 of 530 +/- 100 K is derived, a value significantly less than the 850-1100 K reported for Jovian H-3(+) in the near-infrared but consistent with the temperature reported for fundamental-band quadrupole H-2 emission. Comparison with the Faint Object Camera (FOC) images shows that the observed region was not one of the hot spots of the aurora. The results are interpreted in terms of electron impact excitation of H-2 from secondary particles generated by primaries precipitating into Jupiter's atmosphere from the magnetosphere. In the region of the aurora observed, the homopause level is found to be significantly hotter but not necessarily higher than observed at nonauroral latitudes. The equatorial H-2 dayglow spectrum was also detected; its intensity was 3.2 kR or 13% of the strength of the observed auroral emission. [less ▲]

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See detailMorphology and time variation of the Jovian Far UV aurora: Hubble Space Telescope observations
Gérard, Jean-Claude ULg; Dols, Vincent; Paresce, Francesco et al

in Journal of Geophysical Research (1993), 98

High spatial resolution images of the north polar region of Jupiter have been obtained with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). The first set of two images collected ... [more ▼]

High spatial resolution images of the north polar region of Jupiter have been obtained with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). The first set of two images collected 87 min apart in February 1992 shows a bright (approximately or equal to 180 kR) emission superimposed on the background in rotation with the planet. Both Ly alpha images show common regions of enhanced emission but differences are also observed, possibly due to temporal variations. The second group of images obtained on June 23 and 26, 1992 isolates a spectral region near 153 nm dominated by the H2 Lyman bands and continuum. Both pictures exhibit a narrow arc structure fitting the L = 30 magnetotail field line footprint in the morning sector and a broader diffuse aurora in the afternoon. They show no indication of an evening twilight enhancement. Although the central meridian longitudes were similar, significant differences are seen in the two exposures, especially in the region of diffuse emission, and interpreted as signatures of temporal variations. The total power radiated in the H2 bands is approximately or equal to 2 x 10[SUP]12[/SUP] W, in agreement with previous UV spectrometer observations. The high local H2 emission rates (approximately 450 kR) imply a particle precipitation carrying an energy flux of about 5 x 10[SUP]-2[/SUP] W/sq m. [less ▲]

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See detailEffect of hot N(4S) atoms on the NO solar cycle variation in the lower thermosphere
Gérard, Jean-Claude ULg; Shematovich, V. I.; Bisikalo, D. V.

in Journal of Geophysical Research (1993), 98

The variation of the nitric oxide peak density near 110 km with solar activity is calculated using a photochemical diffusive model of thermospheric odd nitrogen. This model includes the reaction of ... [more ▼]

The variation of the nitric oxide peak density near 110 km with solar activity is calculated using a photochemical diffusive model of thermospheric odd nitrogen. This model includes the reaction of translationally excited ('hot') nitrogen atoms with O2 as a source of nitric oxide, in addition to the classical photochemistry. It is confirmed that the dissociation of N2 by energetic photoelectrons due to the ionization of atmospheric constituents by solar soft X-rays is an important source of atomic nitrogen which controls the observed NO maximum near 110 km. The consideration of the hot N(4S) source increases the NO peak density by 45 to 60 percent dependent on the solar activity level considered. The calculated NO peak density increases by a factor of about 3.5 from low to high solar activity conditions, in agreement with the Solar Mesosphere Explorer satellite observations. The absolute concentrations calculated in the model with an N(2D) effective yield of 54 percent from N2 electron impact dissociation are midway between the two sets of solar cycle NO variation measurements currently available. [less ▲]

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See detailHigh-latitude ion transport and energetic explorer (HI-LITE): a mission to investigate ion outflow from the high-latitude ionosphere
Smith, Mark F; Herrero, Federico A; Hesse, Michael et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (1993, July 01)

The proposed HI-LITE Explorer will investigate the global ion outflow from the high-latitude ionosphere, its relationship to auroral features, and the consequences of this outflow on magnetospheric ... [more ▼]

The proposed HI-LITE Explorer will investigate the global ion outflow from the high-latitude ionosphere, its relationship to auroral features, and the consequences of this outflow on magnetospheric processes. The unique nature of the HI-LITE Explorer images will allow temporal and spatial features of the global ion outflow to be determined. The mission's scientific motivation comes from the fundamental role high-latitude ionospheric ions play in the dynamics of the solar wind driven magnetospheric-ionospheric system. These outflows are a major source of plasma for the magnetosphere and it is believed they play an important role in the triggering of substorms. In addition this paper describes the HI-LITE spacecraft and instruments. [less ▲]

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See detailModeling the Emergent Profiles and Intensities of Lyman Alpha and H[SUB]2[/SUB] Bands Induced by Protons Precipitation in the Jovian Atmosphere
Rego, D.; Prangé; Benjaffel, L. et al

in Bulletin of the American Astronomical Society (1993, June 01)

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