References of "Gérard, Jean-Claude"
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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)

Not Available

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See detailA first look at the ASSI ultraviolet results
Chakrabarti, S.; Gladstone, G. R.; Tobiska, W. K. et al

in Advances in Space Research (1993), 13

The Airglow and Solar Spectrometer Instrument (ASSI) on the San Marco D satellite has obtained near-simultaneous measurements of solar irradiances and airglow emissions in the 200-7000 A spectral region ... [more ▼]

The Airglow and Solar Spectrometer Instrument (ASSI) on the San Marco D satellite has obtained near-simultaneous measurements of solar irradiances and airglow emissions in the 200-7000 A spectral region. The satellite was placed in an equatorial, elliptical orbit on 25 March 1988, which permitted observations of airglow emissions in the 280-600-km altitude range at various local times. The instrument complement on the satellite provides an opportunity both for self-consistent examination of the excitation mechanisms of various airglow features and for constraining model parameters. An overview of the data obtained by ASSI is presented along with preliminary modeling results of the UV airglow. [less ▲]

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See detailCoupled modelling of the global chemical-climatic changes due to human activities
Gérard, Jean-Claude ULg; François, Louis ULg; Delire, C. et al

in Proceedings of the global change symposium (1993)

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See detailThe thermospheric odd nitrogen photochemistry - Role of non thermal N(4S) atoms
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Annales Geophysicae [= ANGEO] (1992), 10

A nonequilibrium model to calculate the Maxwellian 'hot' N(4S) atom population using a Monte Carlo method is developed, and the NO vertical distribution for minimum solar cycle conditions is calculated ... [more ▼]

A nonequilibrium model to calculate the Maxwellian 'hot' N(4S) atom population using a Monte Carlo method is developed, and the NO vertical distribution for minimum solar cycle conditions is calculated. It is shown that the energetic photoelectrons produced by solar soft X-rays produce translationally 'hot' N(4S) atoms near 110 km which contribute significantly to the formation of the E-region NO peak observed at this altitude. Consideration of this new source of nitric oxide reconciles the need for an effective N(2D) quantum yield from N2 dissociation exceeding 50 percent derived from odd nitrogen models with the limits put on this value by laboratory and theoretical constraints. The altitude of the modeled NO peak is found to critically depend on the adopted N(2D) yield, and good agreement with the observed peak altitude and density is obtained using the quantum yield derived from theoretical considerations. [less ▲]

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See detailUltraviolet imaging of the Jovian aurora with the Hubble Space Telescope
Dols, V.; Gérard, Jean-Claude ULg; Paresce, F. et al

in Geophysical Research Letters (1992), 19

We present here for the first time a Lyman-alpha image of the north polar region of Jupiter obtained with the Faint Object Camera on board the Hubble Space Telescope a few hours after the encounter of the ... [more ▼]

We present here for the first time a Lyman-alpha image of the north polar region of Jupiter obtained with the Faint Object Camera on board the Hubble Space Telescope a few hours after the encounter of the ULYSSES spacecraft with Jupiter. The presence of high latitude regions of enhanced emission is clearly observed. A comparison with the location of the 'UVS oval', the Io (L = 6) and high-latitude field-line footprints shows that the best agreement is obtained with the L not less than 15 footprint and the UVS oval which are close to each other for the particular longitudinal sector observed. These two L-shells correspond to two possible sources of precipitation: particles originating respectively from the region of the plasma torus of Io in a distorted magnetic field or particles from the distant magnetosphere by analogy with the terrestrial aurora. [less ▲]

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See detailSolar system observations with HST
Paresce, Francesco; Gérard, Jean-Claude ULg

in Environment Observation and Climate Modelling Through International Space Projects (1992)

Imaging and spectrographic measurements of solar system objects with the Hubble Space Telescope (HST) are reviewed from a scientific and technical standpoint. Special emphasis is placed on observations of ... [more ▼]

Imaging and spectrographic measurements of solar system objects with the Hubble Space Telescope (HST) are reviewed from a scientific and technical standpoint. Special emphasis is placed on observations of Jupiter and Io during the Ulysses encounter by the Faint Object Camera and HRS. The bottom line is that, although the mirror aberration limits HST's extragalactic performance, the potential for a deep systematic probe of planetary conditions over a wide range of observing conditions is still practically intact and will get better as the bugs are ironed out and the COSTAR (Corrective Optics Space Telescope Axial Replacement) fix is implemented. [less ▲]

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See detailObservations of the H and H[SUB]2[/SUB] Ultraviolet Jovian Aurora with the HST Faint Object Camera
Gérard, Jean-Claude ULg; Dols, V.; Paresce, F. et al

in Bulletin of the American Astronomical Society (1992, June 01)

Not Available

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See detailA Model of Lyman ë± and H[SUB]2[/SUB] Bands Excitation by Protons Precipitation in the Jovian Atmosphere
Rego, D.; Prangé; Gérard, Jean-Claude ULg

in Bulletin of the American Astronomical Society (1992, June 01)

Not Available

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See detailThe climate induced variation of the continental biosphere: A model simulation of the last glacial maximum
Friedlingstein, P.; Delire, C.; Müler, J. F. et al

in Geophysical Research Letters (1992), 19

A simplified three-dimensional global climate model was used to simulate the surface temperature and precipitation distributions for the Last Glacial Maximum (LGM), 18000 years ago. These fields were ... [more ▼]

A simplified three-dimensional global climate model was used to simulate the surface temperature and precipitation distributions for the Last Glacial Maximum (LGM), 18000 years ago. These fields were applied to a bioclimatic scheme which parameterizes the distribution of eight vegetation types as a function of biotemperature and annual precipitation. The model predicts a decrease, for LGM compared to present, in forested area balanced by an increase in desert and tundra extent, in agreement with a reconstruction of the distribution of vegetation based on paleodata. However, the estimated biospheric carbon content (phytomass and soil carbon) at LGM is less reduced than in the reconstructed one. Possible reasons for this discrepancy are discussed. [less ▲]

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See detailThermospheric odd nitrogen
Gérard, Jean-Claude ULg

in Planetary and Space Science (1992), 40

The photochemistry of NO, N(2D) and N(4S) and results of recent space measurements of their density distribution are discussed. In particular, the role of the reaction between metastable N(2D) atoms and ... [more ▼]

The photochemistry of NO, N(2D) and N(4S) and results of recent space measurements of their density distribution are discussed. In particular, the role of the reaction between metastable N(2D) atoms and O2 as a source of O(1D) is discussed in the light of laboratory and aeronomical observations. Global satellite measurements are compared with results of 2D and 3D models including transport. The possibility of explaining the odd nitrogen observations gathered in the Venusian and Martian thermospheres with the current understanding of the terrestrial models adapted to CO2-rich atmospheres is examined. It is concluded that understanding of the processes governing the distribution of odd nitrogen in terrestrial planets is generally satisfactory, although several aspects require further quantitative investigation. [less ▲]

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See detailHigh Resolution Near UV Observations of Jupiter's Satellite Io with HST
Paresce, F.; Sartoretti, P.; Dols, V. et al

in Benvenuti, Piero; Schreier, Ethan J. (Eds.) Science with the Hubble Space Telescope, (1992)

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See detailObservations and physical properties of small solar system bodies
Gérard, Jean-Claude ULg; Brahic, André; Surdej, Jean ULg

Book published by Université de Liège (1992)

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See detailA sensitivity study of the role of continental area and location on Paleozoic climate
Hauglustaine, Didier A.; Gérard, Jean-Claude ULg

in Global and Planetary Change (1992), 97

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See detailThe faint young sun climatic paradox: A simulation with an interactive seasonal climate-sea ice model
Gérard, Jean-Claude ULg; Hauglustaine, Didier A.; François, Louis ULg

in Global and Planetary Change (1992), 97(3), 133-150

A seasonal one-and-a-half-dimensional (1 1/2-D) energy-balance climate model including a detailed sea ice calculation and an interactive albedo formulation has been developed and is used to investigate ... [more ▼]

A seasonal one-and-a-half-dimensional (1 1/2-D) energy-balance climate model including a detailed sea ice calculation and an interactive albedo formulation has been developed and is used to investigate the faint young sun climatic paradox. This model is shown to reproduce the present climate and sea ice observations. In spite of its greater complexity, its behavior is globally similar to simple energy-balance models with highly parameterized ice-albedo feedback used in previous studies of this question. It is found that when the solar luminosity drops by more than about 5% below its present value, the ice albedo feedback causes a global irreversible glaciation. Several sensitivity experiments show that the value of the critical solar constant and associated global surface temperature are only little sensitive to the set of model parameters describing the ice and snow albedo and meridional heat transport. In contrast, the absence or polar location of the continental mass introduce a nearly 10% decrease of the critical luminosity. The minimum level of atmospheric CO2 needed to prevent a global glaciation through enhanced greenhouse warming is calculated as a function of the solar luminosity. A 30% drop in solar output requires a 2 x 10(4)-fold increase in atmospheric CO2, an unacceptably large value. However, in the absence of continents, a carbon dioxide partial pressure of 2000 times the present level is found to be sufficient to stabilize the climate. The effects of a reduced continental area, paleogeographic changes and higher CO2 greenhouse effect combine to ensure a larger stability of the non-frozen configuration. Their cumulated and interactive effects may be able to solve the young sun paradox. [less ▲]

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See detailFar ultraviolet imaging of Jupiter's northern polar regions with the FOC
Gérard, Jean-Claude ULg; Dols, V.; Paresce, F. et al

in Science with the Hubble Space Telescope (1992)

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See detailThe thermospheric odd nitrogen photochemistry: role of non thermal N(4S) atoms
Shematovich, V.; Bisikalo, D.; Gérard, Jean-Claude ULg

in Geophysical Research Letters (1992), 10

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See detailNon thermal nitrogen atoms in the earth's thermosphere. I - Kinetics of hot N(4S). II - A source of nitric oxide
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Geophysical Research Letters (1991), 18

The energy distribution of translationally hot nitrogen atoms in the thermosphere has been calculated using a nonequilibrium kinetic model. Dissociation by solar EUV photons and photoelectrons is found to ... [more ▼]

The energy distribution of translationally hot nitrogen atoms in the thermosphere has been calculated using a nonequilibrium kinetic model. Dissociation by solar EUV photons and photoelectrons is found to provide an important source of non-Maxwellian high energy N(4S) atoms. It is shown that quenching of metastable N(2D) atoms by atomic oxygen also produces significant amounts of hot N(4S) atoms. The fraction of hot N atoms reacting with O2 is found to be about 15 percent of the production rate of atomic nitrogen by N2 dissociation by photon and photoelectron impact and quenching of N(2D) metastable atoms by atomic oxygen. The very fast reaction between hot N(4S) atoms and O2 is shown to provide an additional source of nitric oxide. At equatorial latitudes, this contribution amounts to 6-30 percent of the other classical production sources of NO for solar minimum activity conditions. It is concluded that the effect of hot N atoms must be considered in future models of the NO-N system chemistry. [less ▲]

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See detailNon thermal nitrogen atoms in the Earth's thermosphere. 2. A source of nitric oxide
Gérard, Jean-Claude ULg; Shematovich, V. I.; Bisikalo, D. V.

in Geophysical Research Letters (1991), 18

The role of the non maxwellian nitrogen atoms in the odd nitrogen thermospheric chemistry is investigated with a numerical model. This one-dimensional model solves the continuity equation, including ... [more ▼]

The role of the non maxwellian nitrogen atoms in the odd nitrogen thermospheric chemistry is investigated with a numerical model. This one-dimensional model solves the continuity equation, including molecular and turbulent transport for the coupled NO-N([SUP]4[/SUP]S) system. It is shown that the very fast reaction between hot N([SUP]4[/SUP]S) atoms and O[SUB]2[/SUB] provides an additional source of nitric oxide. At equatorial latitudes, this contribution amounts to 6-30% of the other classical production sources of NO for solar minimum activity conditions. The cross section for elastic collisions with ambient gas introduces the largest uncertainty on this estimate. It is concluded that, although it does not drastically alter the conclusions of previous models of NO, the effect of hot N atoms must be considered in future models of the NO-N system chemistry. [less ▲]

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See detailThe diurnal variation of NO, N(D-2), and ions in the thermosphere - A comparison of satellite measurements to a model
Rusch, D. W.; Gérard, Jean-Claude ULg; Fesen, C. G.

in Journal of Geophysical Research (1991), 96

A data base of parameters important to understanding the diurnal variation of odd-nitrogen and ions in the thermosphere near equinox, at low latitudes, and for quiet geomagnetic conditions is presented ... [more ▼]

A data base of parameters important to understanding the diurnal variation of odd-nitrogen and ions in the thermosphere near equinox, at low latitudes, and for quiet geomagnetic conditions is presented. The data base includes profiles of the odd-nitrogen species NO and N(D-2), the ions NO(+), O2(+), O(+), N2(+), and N(+); the total ion density; O and N2; and the neutral, ion, and electron temperatures. The measured time-dependent variations of NO, N(D-2), O2(+), and NO(+) compare favorably to the results of a time-dependent, photochemical, diffusion model for odd-nitrogen and ion chemistry. In particular, the model reproduces the rapid increase in NO density in the morning hours, the midafternoon maximum, and the late afternoon decrease. The model also reproduces the measured absolute densities for NO to within 20 percent over most of the diurnal cycle but falls below the measured density by as much as a factor of two in the late afternoon. [less ▲]

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