References of "Gérard, Jean-Claude"
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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)

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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)

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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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See detailThe atmosphere's response to solar irradiation
Hunten, D. M.; Gérard, Jean-Claude ULg; François, Louis ULg

in Sonnett, C. P.; Giampapa, M. S.; Matthews, M. S. (Eds.) The Sun in time (1991)

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See detailPast and Future CFC and other trace gas warming: results from a seasonal climate model
Hauglustaine, Didier A.; Gérard, Jean-Claude ULg

in Annales Geophysicae [= ANGEO] (1991), 9

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See detailObservations ultraviolettes des planètes géantes et de leurs satellites à l'aide du Télescope Spatial Hubble
Gérard, Jean-Claude ULg; Dols, Vincent

in Nouvelles de la Science et des Technologies (1991)

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See detailThe latitudinal gradient of the NO peak density
Fesen, C. G.; Rusch, D. W.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1990), 95

Results are presented from SME observations of the latitudinal gradients of peak NO densities at about 110-km altitude during the solstice and equinox periods from 1982 through 1985. It is shown that the ... [more ▼]

Results are presented from SME observations of the latitudinal gradients of peak NO densities at about 110-km altitude during the solstice and equinox periods from 1982 through 1985. It is shown that the response of the peak NO densities to the declining level of solar activity varies with latitude, with the polar regions exhibiting low sensitivity and the low-latitude regions responding strongly. The SME data also revealed marked asymmetries in the latitudinal structure of the two hemispheres for each season and considerable day-to-day variations in the NO densities. The solar cycle minimum data for June were simulated using a two-dimensional model; results of sensitivity studies performed with varied quenching rate and eddy diffusion coefficient are presented. [less ▲]

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See detailThe warm Cretaceous climate - Role of the long-term carbon cycle
Gérard, Jean-Claude ULg; Dols, Vincent

in Geophysical Research Letters (1990), 17

An annual energy-balance model is coupled to a steady state formulation of the long-term CO2 cycle to investigate the possible sources of global warming of the Cretaceous period. It is found that ... [more ▼]

An annual energy-balance model is coupled to a steady state formulation of the long-term CO2 cycle to investigate the possible sources of global warming of the Cretaceous period. It is found that paleogeography solely is an insufficient factor but that the different latitudinal distribution of continental masses 100 My ago influenced the CO2 cycle and favored a larger content of the atmospheric CO2 level. A larger rate of tectonic activity and the possible influence of the vegetation in a CO2 richer atmosphere provide further sources of atmospheric carbon dioxide increase. The combination of these factors, together with a more vigorous poleward heat transport, provides CO2 levels 5 to 15 times larger than today and a global surface warming within the 6-1 C estimated from paleoindicators. [less ▲]

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See detailSolar cycle variation of thermospheric nitric oxide at solstice
Gérard, Jean-Claude ULg; Fesen, C. G.; Rusch, D. W.

in Journal of Geophysical Research (1990), 95

A coupled, two-dimensional, chemical-diffusive model of the thermosphere is used to study the role of solar activity in the global distribution of nitric oxide. The model calculates self-consistently the ... [more ▼]

A coupled, two-dimensional, chemical-diffusive model of the thermosphere is used to study the role of solar activity in the global distribution of nitric oxide. The model calculates self-consistently the zonally averaged temperature, circulation, and composition for solstice under solar maximum and solar minimum conditions. A decrease of the NO density by a factor of three to four in the E region is predicted from solar maximum to solar minimum. It is found that the main features of the overall morphology and the changes induced by the solar cycle are well reproduced in the model, although some details are not satisfactorily predicted. The sensitivity of the NO distribution to eddy transport and to the quenching of metastable N(2D) atoms by atomic oxygen is also described. [less ▲]

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