References of "Gérard, Jean-Claude"
     in
Bookmark and Share    
Peer Reviewed
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

Detailed reference viewed: 7 (1 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 52 (9 ULg)
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)

Detailed reference viewed: 15 (3 ULg)
Peer Reviewed
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

Detailed reference viewed: 6 (1 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 9 (3 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 1 (0 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 5 (0 ULg)
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)

Detailed reference viewed: 16 (1 ULg)
Peer Reviewed
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

Detailed reference viewed: 11 (5 ULg)
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)

Detailed reference viewed: 2 (1 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 10 (0 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 14 (1 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 11 (0 ULg)
Peer Reviewed
See detailThe Venus nitric oxide night airglow - Model calculations based on the Venus Thermospheric General Circulation Model
Bougher, S. W.; Gérard, Jean-Claude ULg; Stewart, A. I. F. et al

in Journal of Geophysical Research (1990), 95

The mechanism responsible for the Venus nitric oxide (0,1) delta band nightglow observed in the Pioneer Venus Orbiter UV spectrometer (OUVS) images was investigated using the Venus Thermospheric General ... [more ▼]

The mechanism responsible for the Venus nitric oxide (0,1) delta band nightglow observed in the Pioneer Venus Orbiter UV spectrometer (OUVS) images was investigated using the Venus Thermospheric General Circulation Model (Dickinson et al., 1984), modified to include simple odd nitrogen chemistry. Results obtained for the solar maximum conditions indicate that the recently revised dark-disk average NO intensity at 198.0 nm, based on statistically averaged OUVS measurements, can be reproduced with minor modifications in chemical rate coefficients. The results imply a nightside hemispheric downward N flux of (2.5-3) x 10 to the 9th/sq cm sec, corresponding to the dayside net production of N atoms needed for transport. [less ▲]

Detailed reference viewed: 13 (2 ULg)
Peer Reviewed
See detailModelling the Climatic Response to Solar Variability: Discussion
Pecker, J*-C; Gérard, Jean-Claude ULg

in Royal Society of London Philosophical Transactions Series A (1990), 330

Not Available

Detailed reference viewed: 11 (0 ULg)
Peer Reviewed
See detailModelling the Climatic Response to Solar Variability
Gérard, Jean-Claude ULg

in Royal Society of London Philosophical Transactions Series A (1990), 330

The Sun, the primary energy source driving the climate system, is known to vary in time both in total irradiance and in spectral composition in the ultraviolet. According to solar interior evolution ... [more ▼]

The Sun, the primary energy source driving the climate system, is known to vary in time both in total irradiance and in spectral composition in the ultraviolet. According to solar interior evolution models, the solar luminosity has increased steadily by 25-30% over the past 4 × 10[SUP]9[/SUP] years. Periodic variations are also suspected with characteristic timescales of 11 or 22 years, 80-90 years and possibly longer periods. The ultraviolet radiation below 300 nm also exhibits significant changes over the 27-day solar rotation period as well as the 11-year solar cycle. Variations in the solar constant are expected to produce both direct and indirect (feedback) perturbations in the global surface temperature. A hierarchy of zero- to three-dimensional models have been used to study the complex couplings involved by such effects. The response of a zonally averaged model to possible total irradiance changes associated with the Gleissberg cycle is investigated and compared with measurements of the sea-surface temperature made since 1860. Changes in the solar ultraviolet irradiance modulate the amount and distribution of atmospheric ozone, which is predicted to change by several percent in the stratosphere. These perturbations directly affect the middle atmospheric thermal structure, but may also generate indirect effects that could possibly account for some short-term geophysical signatures of solar activity. The cycle-modulated energetic particle interaction with the middle atmosphere is also a possible source of global climatic perturbations. [less ▲]

Detailed reference viewed: 18 (5 ULg)
See detailObservation ultraviolette des planètes géantes et de leurs satellites à l'aide du téléescope spatial Hubble
Gérard, Jean-Claude ULg; Dols, V.

in Nouvelles de la Science et des Technologies (1990), 8(3-4), 43-46

Detailed reference viewed: 6 (0 ULg)
Peer Reviewed
See detailPOSSIBLE COMPOSITION AND CLIMATIC CHANGES DUE TO PAST INTENSE ENERGETIC PARTICLE-PRECIPITATION
Hauglustaine, Didier A.; Gérard, Jean-Claude ULg

in Annales Geophysicae [= ANGEO] (1990), 8(2), 87-96

Detailed reference viewed: 28 (4 ULg)
See detailModelling the climatic response to solar variability.
Gérard, Jean-Claude ULg

in The Earth's Climate and Variability of the Sun over Recent Millennia: Geophysical, Astronomical and Archaeological Aspects (1990)

The author summarizes the available evidence for intrinsic solar variability and describes the climatic consequences of such variations as predicted by current models. He presents model calculations of ... [more ▼]

The author summarizes the available evidence for intrinsic solar variability and describes the climatic consequences of such variations as predicted by current models. He presents model calculations of the possible temperature signature of the Gleissberg solar cycle and climatic effects of ultraviolet irradiance variations and intense solar charged particle interaction with the Earth's atmosphere. [less ▲]

Detailed reference viewed: 19 (6 ULg)