References of "Gérard, Jean-Claude"
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See detailHigh color ratio and high temperature in Jupiter's auroral atmosphere
Grodent, Denis ULiege; Gustin, Jacques ULiege; Gérard, Jean-Claude ULiege et al

Poster (2001, October 27)

A high FUV color ratio usually implies that most of the energy of the impinging auroral particles is deposited below the methane homopause. In this region, the resulting auroral heating is efficiently ... [more ▼]

A high FUV color ratio usually implies that most of the energy of the impinging auroral particles is deposited below the methane homopause. In this region, the resulting auroral heating is efficiently balanced by the strong hydrocarbon cooling. Therefore, this auroral process cannot sustain the high temperature observed in the Jovian auroral atmosphere. This work is an attempt to remove the ambiguity between the high color ratios and high temperatures deduced from the HST data. In order to study this apparent contradiction, the two-stream energy deposition model described by Grodent et al. (2001) has been upgraded with a Joule heating module and an adiabatic cooling approximation. The most recent hydrocarbon auroral density profiles have been included. A new EUV-FUV spectral generator has been developed and allows one to consider new observational constrains, such as the very high H2 scale heights deduced from the Cassini-Jupiter flyby HST observations. [less ▲]

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Peer Reviewed
See detailThe role of proton precipitation in the excitation of auroral FUV emissions
Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege; Bisikalo, D. V. et al

in Journal of Geophysical Research (2001), 106

Far ultraviolet remote sensing from a high-altitude satellite is extensively used to image the global aurora, derive its energetics, and follow its dynamical morphology. It is generally assumed that the ... [more ▼]

Far ultraviolet remote sensing from a high-altitude satellite is extensively used to image the global aurora, derive its energetics, and follow its dynamical morphology. It is generally assumed that the observed emissions are dominated by the interaction of the precipitated electrons with the thermospheric constituents. A model to calculate far ultraviolet emissions excited by auroral electrons and protons and the secondary electrons they generate has been used to calculate the volume excitation rate of the H I Ly-alpha, O I 1304 and 1356 Å, N I 1493 Å multiplets, and the N[SUB]2[/SUB] Lyman-Birge-Hopfield (LBH) bands. The characteristic energy and the energy flux are derived from the observed statistical distribution of precipitated protons and electrons. This model is applied to the midnight aurora, the noon cusp, and a proton-dominated aurora for moderately disturbed conditions. We show that in the first two cases, direct electron impact dominates the vertically integrated emission rate over the proton component, although proton excitation plays an important role at some altitudes in the daytime cusp. In afternoon regions of the auroral zone near the auroral boundary, secondary electrons due to proton ionization are the main source of FUV emissions. The energy dependence of the efficiency of LBH band emission viewed from high altitude is calculated for electron and proton precipitations. Maps of the N[SUB]2[/SUB] LBH emission excited by both components are obtained, and regions of proton-dominated auroral emission are identified. It is found that the distribution of the ratio of proton-induced to electron-induced brightness resembles maps of the ratio of the respective precipitated energy fluxes. Proton-dominated FUV emissions are thus located in a C-shaped sector extending from prenoon to midnight magnetic local times with a maximum proton contribution near the equatorward boundary of the statistical electron oval. The distribution of the Ly-alpha/LBH intensity ratio is found to mimic the ratio of the proton flux/total energy flux, although it is insufficient by itself to accurately determine the relative fraction of auroral energy carried by the protons. [less ▲]

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See detailElectron and Proton Auroral Dynamics
Mende, S. B.; Frey, H. U.; Carlson, C. et al

Conference (2001, May 01)

Data from the IMAGE Wide-band Imaging Camera (WIC),sensitive to far ultraviolet auroras and from the Spectrographic Imager (SI) channel SI12, sensitive to proton precipitation induced Lyman alpha, were ... [more ▼]

Data from the IMAGE Wide-band Imaging Camera (WIC),sensitive to far ultraviolet auroras and from the Spectrographic Imager (SI) channel SI12, sensitive to proton precipitation induced Lyman alpha, were analyzed during a high altitude orbit segment of the IMAGE spacecraft. This segment began during the expansive phase of a substorm. The aurora developed into a double oval configuration, consisting of a set of discrete poleward forms and a separate diffuse auroral oval equatorwards. Although IMF Bz was negative, considerable activity could be seen poleward of the high latitude arcs in the polar cap region. The optical signature of precipitating protons showed that the proton aurora was on the equatorward side of the diffuse aurora and there was a lack of intense energetic proton fluxes in the poleward arcs. A simultaneous FAST pass provided a diagnostic of the particle types in the various regions. These data showed that lower intensity protons were present throughout the entire double oval configuration but with insufficient intensity to produce aurora that could be observed by IMAGE. The FAST data also showed that the bright poleward discrete arcs were accelerated by electrostatic processes, and the wave accelerated electrons were located on the poleward edge of these features. [less ▲]

Detailed reference viewed: 31 (2 ULiège)
See detailCusp studies with IMAGE-FUV
Frey, H. U.; Mende, S. B.; Fuselier, S. A. et al

Conference (2001, May 01)

The FUV instrument on IMAGE frequently observes localized ultraviolet emission on the high latitude dayside, poleward of the normal auroral oval location. This emission is especially distinct in the ... [more ▼]

The FUV instrument on IMAGE frequently observes localized ultraviolet emission on the high latitude dayside, poleward of the normal auroral oval location. This emission is especially distinct in the observations of Doppler shifted Lyman alpha emission from precipitating protons. We interpret this emission as the optical signature of precipitation into the cusp after lobe reconnection at the magnetopause. Several cusp crossings by the FAST satellite are used to establish an estimate of the energy input and the characteristics of the precipitating protons. Multivariate cluster analysis and other statistical tools are used to determine the dependence of this precipitation on solar wind parameters. This shows that under northward IMF and high solar wind dynamic pressure, proton precipitation can be the dominating energy input into the cusp region. [less ▲]

Detailed reference viewed: 18 (1 ULiège)
See detailDetermination of electron and proton auroral energy inputs from FUV-IMAGE
Gérard, Jean-Claude ULiege; Hubert, Benoît ULiege; Meurant, M. et al

Conference (2001, May 01)

The FUV experiment onboard the IMAGE spacecraft offers the unique possibility to obtain simultaneous snapshots of the global north aurora every 2 minutes in three different spectral channels. The WIC ... [more ▼]

The FUV experiment onboard the IMAGE spacecraft offers the unique possibility to obtain simultaneous snapshots of the global north aurora every 2 minutes in three different spectral channels. The WIC camera has a broadband channel covering the 135-190 nm interval including the N[SUB]2[/SUB] LBH bands, part of which may be absorbed by O[SUB]2[/SUB]. The SI13 channel is centered on the OI 135.6 nm line which is optically thin and includes a ~ 40% LBH contribution. Finally, the SI12 camera images the Doppler-shifted Ly-α emission excited by the proton aurora. This set of instrumentation is combined with auroral models to determine the electron and the proton energy fluxes from the magnetosphere. Examples will be presented and compared with the values deduced from the NOAA satellites. Simultaneous in-situ measurements of the particle characteristic energy have been combined with the data extracted from the FUV images to validate the models and derive empirical relationships between the particle flux measured by the detectors and the brightness observed by FUV-IMAGE at the footprint of the same magnetic field line. Finally, we will assess the ability to deduce the characteristic energy of the auroral particles from the ratio of co-registered images in the WIC and SI13 cameras. This method is based on the difference of vertical distribution of the LBH and the OI 135.6 nm emissions. It offers the potential to globally remotely sense not only the energy flux from the magnetosphere but also the main features of the electron characteristic energy. [less ▲]

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See detailDerivation of Auroral Conductances from IMAGE FUV
Immel, T. J.; Mende, S. B.; Frey, H. U. et al

Conference (2001, May 01)

Auroral emissions are observed in 3 separate Far-Ultraviolet (FUV) wavelength regimes by IMAGE. The Wideband Imaging Camera (WIC) is sensitive mainly to N[SUB]2[/SUB] LBH and N I emissions in the 140-190 ... [more ▼]

Auroral emissions are observed in 3 separate Far-Ultraviolet (FUV) wavelength regimes by IMAGE. The Wideband Imaging Camera (WIC) is sensitive mainly to N[SUB]2[/SUB] LBH and N I emissions in the 140-190-nm range, while the Spectrographic Imager (SI) spectrally separates the OI 135.6-nm emission and Doppler shifted hydrogen emissions of the proton aurora at 121.8 nm. The brightness of the N[SUB]2[/SUB] LBH and OI 135.6-nm emissions depend in part on the spectrum and total energy flux of incoming electrons, and on the height-density profile of the respective species, and O[SUB]2[/SUB]. Due mainly to these atmospheric factors, the ratio of the N[SUB]2[/SUB] and OI emissions depends strongly on the characteristic energy of precipitating electrons which, once estimated, can in turn be used to calculate the total energy flux. The proton aurora generates secondary electrons, which excite additional emissions of N[SUB]2[/SUB] and OI. It is not possible to absolutely determine either the total proton energy flux or the characteristic proton energy (<E[SUB]p[/SUB]>) with a single proton imaging channel. However, the proton-induced N[SUB]2[/SUB] and OI emissions depend mainly on the total proton energy flux, so reasonable estimates of <E[SUB]p[/SUB]> can be used in the calculation of proton energy input. Ground-based or in-situ observations of proton energies can help in this determination. With accurate corrections for N[SUB]2[/SUB] and OI airglow emissions, and formulae such as those provided by Robinson et al. [1987], IMAGE FUV can provide global maps of height-integrated conductivity (conductance) in the auroral oval. It is also possible to examine the degree to which the proton aurora contributes to enhanced conductance on a global scale. The promise of providing these conductances using IMAGE's real-time capabilities will be discussed. Robinson, R. M., R. R. Vondrak, K. Miller, T. Dabbs, and D. Hardy, On Calculating Ionospheric Conductances from the Flux and Energy of Precipitating Electrons, J. Geophys. Res., 92, 2566, 1987. [less ▲]

Detailed reference viewed: 21 (2 ULiège)
Peer Reviewed
See detailThe electron and proton aurora as seen by IMAGE-FUV and FAST
Frey, H. U.; Mende, S. B.; Carlson, C. W. et al

in Geophysical Research Letters (2001), 28

The Far Ultraviolet Instrument (FUV) on the IMAGE spacecraft observes the aurora in three different channels. One of them (SI12) is sensitive to the signal from precipitating protons, while the other two ... [more ▼]

The Far Ultraviolet Instrument (FUV) on the IMAGE spacecraft observes the aurora in three different channels. One of them (SI12) is sensitive to the signal from precipitating protons, while the other two (WIC and SI13) observe auroral emissions which are not only excited by precipitating electrons, but also by protons. We examine a period when in-situ particle measurements by the FAST spacecraft were available simultaneously with global imaging with FUV. The measured electron and proton energy spectra are used to calculate the auroral brightness along the FAST orbit. The comparison with the FUV/IMAGE observations shows good quantitative agreement and demonstrates that under certain circumstances high proton fluxes may produce significant amounts of auroral FUV emission. [less ▲]

Detailed reference viewed: 19 (1 ULiège)
Peer Reviewed
See detailGlobal observations of proton and electron auroras in a substorm
Mende, S. B.; Frey, H. U.; Lampton, M. et al

in Geophysical Research Letters (2001), 28

This is the first report of a substorm observed by the IMAGE FUV instruments permitting global observations of electron and proton produced auroras. On the 28th of June 2000 at 1956 UT in the pre-substorm ... [more ▼]

This is the first report of a substorm observed by the IMAGE FUV instruments permitting global observations of electron and proton produced auroras. On the 28th of June 2000 at 1956 UT in the pre-substorm phase at early evening local time the proton aurora was equatorward of the electron precipitation and near midnight they were collocated. There was bright electron and proton aurora in the post midday afternoon side. The sudden brightening of the aurora at substorm onset near midnight is seen in the electrons only although there are protons present at this location. During the expansive phase both the electrons and protons expand poleward. The electron aurora forms a bright surge at the poleward boundary while the protons just show diffuse spreading. The peak intensity of the protons did not change substantially during the entire event. The proton aurora is brighter on the dusk while the electron aurora on the dawn side. As the electron surge expands poleward it leaves the protons behind. The electrons form a discrete auroral feature near the aurora-polar cap boundary, which is devoid of substantial energetic (>1 keV) proton precipitation. The presence of precipitating protons at the point where the initial brightening is seen shows that substorms are initiated on closed field lines. [less ▲]

Detailed reference viewed: 49 (0 ULiège)
Peer Reviewed
See detailIon outflow observed by IMAGE: Implications for source regions and heating mechanisms
Fuselier, S. A.; Ghielmetti, A. G.; Moore, T. E. et al

in Geophysical Research Letters (2001), 28

Images of the Earth's proton aurora from the IMAGE spacecraft on 8 June 2000 indicate a temporally and spatially isolated ionospheric response to a shock that impinged on the Earth's magnetopause ... [more ▼]

Images of the Earth's proton aurora from the IMAGE spacecraft on 8 June 2000 indicate a temporally and spatially isolated ionospheric response to a shock that impinged on the Earth's magnetopause. Sometime after this ionospheric response, the Low Energy Neutral Atom imager on IMAGE detected enhanced ionospheric outflow. The time delay between the ionospheric response and the enhanced outflow is consistent with the travel time of ~30 eV neutral Oxygen (created by charge exchange of outflowing O[SUP]+[/SUP] with the exosphere) from the low altitude ionosphere to the spacecraft. The prompt ionospheric outflow implies that the shock deposited sufficient energy in the topside ionosphere near or above the O[SUP]+[/SUP] exobase to initiate the outflow. [less ▲]

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Peer Reviewed
See detailModelling short-term CO2 fluxes and long-term tree growth in temperate forests with ASPECTS
Rasse, Daniel P.; François, Louis ULiege; Aubinet, Marc ULiege et al

in Ecological Modelling (2001), 141(1-3), 35-52

The net ecosystem exchange (NEE) Of CO2 between temperate forests and the atmosphere governs both carbon removal from the atmosphere and forest growth. In recent years, many experiments have been ... [more ▼]

The net ecosystem exchange (NEE) Of CO2 between temperate forests and the atmosphere governs both carbon removal from the atmosphere and forest growth. In recent years, many experiments have been conducted to determine temperate forest NEE. These data have been used by forest modellers to better understand the processes that govern CO, fluxes, and estimate the evolution of these fluxes under changing environmental conditions. Nevertheless, it is not clear whether models capable of handling short-term processes, which are mostly source-driven, can provide an accurate estimate of long-term forest growth, which is potentially more influenced by sink- and phenology-related processes. To analyse the interactions between short- and long-term processes, we developed the ASPECTS model, which predicts long-term forest growth by integrating, over time, hourly NEE estimates. Validation data consisting of measurements of NEE by eddy-covariance and forest carbon reservoir estimates were obtained from mixed deciduous and evergreen experimental forests located in Belgium. ASPECTS accurately estimated both: (1) the NEE fluxes for several years of data; and (2) the amount of carbon contained in stems, branches, leaves, fine and coarse roots. Our simulations demonstrated that: (1) NEE measurements in Belgian forests are compatible with forest growth over the course of the 20th century, and (2) that forest history and long-term processes need to be considered for accurate simulation of short-term CO2 fluxes. [less ▲]

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See detailA self-consistent model of the Jovian auroral thermal structure
Grodent, Denis ULiege; Waite, J. Hunter; Gérard, Jean-Claude ULiege

in Journal of Geophysical Research (2001), 106(A7), 12933-12952

A one-dimensional (1-D) model coupling a two-stream electron transport model of energy deposition with a 1-D thermal conduction model has been developed. It is applied to investigate the links between ... [more ▼]

A one-dimensional (1-D) model coupling a two-stream electron transport model of energy deposition with a 1-D thermal conduction model has been developed. It is applied to investigate the links between auroral heat input and the vertical temperature of Jupiter's upper atmosphere. Two energy distributions meant to reproduce the emissions of a diffuse and a discrete aurora are used to evaluate the importance of the energy spectrum of the incident electrons for the thermal balance of Jupiter's auroral thermosphere. The values of observable quantities such as the altitude of the H-2 emission peak, thermal infrared (LR), ultraviolet (UV) emissions, and temperatures associated with various optical signatures are used to constrain the parameters of these distributions. It is shown that the high-energy component of these energy distributions heats a region of the homosphere between 10(-4) and 10(-6) bar and mainly controls the H-2 temperature and the far-UV (FUV) emission. A 3-keV soft electron component is necessary to heat the region directly above the homopause, between 10(-6) and 10(-9) bar. It has a large influence on the H-2 and H-3(+) temperatures and on the H-3(+) near-IR(NIR) emission. It is used in conjunction with a weak 100 eV component which is responsible for heating the thermosphere, from 10(-9) to 10(-12) bar and exerts a control on the exospheric temperature. The calculated temperatures, UV, and IR emissions suggest that the model probably misses a nonparticle heat source in the 10(-5) bar region, that is expected to balance the strong hydrocarbon cooling. Sensitivity tests are performed to evaluate the importance of the parameters of the energy distributions. They show that the FUV color ratio increases with the characteristic energy (or high-energy cutoff) of the high-energy component, while the H-2 rovibrational temperature varies inversely. A trade-off is therefore necessary for these two parameters to simultaneously meet their observational constraints. Further tests demonstrate the essential thermostatic role played by H-3(+), which regulates the net heating in the thermosphere. An increased eddy diffusion reproduces the effect of a possible auroral upwelling of methane but gives rise to an H-2 temperature smaller than the observed value. [less ▲]

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Peer Reviewed
See detailThe Proton and Electron Aurora as Seen by Image-FUV and FAST
Gérard, Jean-Claude ULiege; Hubert, Benoît ULiege; Habraken, Serge ULiege et al

Conference (2000, December)

The Far Ultraviolet (FUV) instrument on IMAGE images the aurora in three different wavelength regions. The Wideband Imaging Camera (WIC) observes the molecular Lyman-Birge-Hopfield (LBH) and atomic ... [more ▼]

The Far Ultraviolet (FUV) instrument on IMAGE images the aurora in three different wavelength regions. The Wideband Imaging Camera (WIC) observes the molecular Lyman-Birge-Hopfield (LBH) and atomic Nitrogen emissions at 140-190 nm. The two channels of the Spectrographic Imager (SI) observe the Doppler shifted Lyman Alpha emission of precipitating protons at 121.8 nm (SI 12) and the mostly electron produced emission from oxygen OI at 135.6 nm (SI13). The major advantage of FUV compared to previously flown UV imagers is the simultaneous operation of all three imaging systems without the need for filter changes and the uncertainty of temporal changes of the aurora between exposures. The FAST satellite passes every two hours through FUV images during apogee operations. This enables a comparison between the remotely imaged particle precipitation and the in-situ measurements along the FAST track. The detailed analysis of images from all three systems together with a full simulation of auroral emissions based on in-situ measurements by FAST confirms the laboratory calibrations of FUV. The spatial resolution and image quality of WIC permits the observation of a good correspondence between in-situ and remote measurements of precipitation boundaries. The clear separation between the lower latitude proton precipitation and the more structured higher latitude electron precipitation is obtained with both SI-channels. [less ▲]

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See detailStellar calibration of the WIC and SI imagers and the GEO photometers on IMAGE/FUV
Gladstone, G. R.; Mende, S. B.; Frey, H. U. et al

Poster (2000, December)

Detailed reference viewed: 73 (1 ULiège)
See detailA dawn auroral storm on Jupiter: measurement of complex hydocarbons
Clarke, J. T.; Gladstone, R.; Pryor, W. et al

Conference (2000, December)

Detailed reference viewed: 8 (0 ULiège)
See detailHST/STIS Observations of a Dawn Auroral Storm on Jupiter
Clarke, J. T.; Gladstone, R.; Pryor, W. et al

in Bulletin of the American Astronomical Society (2000, October 01)

The HST/STIS recorded a detailed time series of images and spectra of the UV emissions from a dawn auroral storm on Jupiter on 21 Sept. 1999. The images show complex and evolving fine structure in the ... [more ▼]

The HST/STIS recorded a detailed time series of images and spectra of the UV emissions from a dawn auroral storm on Jupiter on 21 Sept. 1999. The images show complex and evolving fine structure in the storm, while the emission center remained along the main oval and near dawn in magnetic local time. We serendipitously recorded low resolution UV spectra of the north-south spatial distribution of the auroral emissions. These spectra show far stronger hydrocarbon absorptions than observed in any previous auroral spectra. This indicates an unusually deep penetration of the incident primary particles with respect to the neutral atmosphere, and correspondingly high energy of the primary particles. We can thus use these spectra to identify many complex hydrocarbons in Jupiter's auroral atmosphere which are not normally measured in auroral spectra. These results will be presented along with model fits to the spectra derived both from fitting the observed hydrocarbon absorption features and from comparison with a photochemical model for the expected composition of the auroral atmosphere. This research has been supported by grant GO-8171.01-97A from the Space Telescope Science Institute to the University of Michigan. [less ▲]

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See detailObservations of substorm auroras from the IMAGE spacecraft
Frey, H. U.; Mende, S. B.; Lampton, M. et al

Conference (2000, October)

Detailed reference viewed: 1 (0 ULiège)
See detailFar ultraviolet imaging of the aurora: new directions
Mende, S. B.; Frey, H. U.; Lampton, M. et al

Conference (2000, October)

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Full Text
See detailAller plus haut, voir de plus près
Gérard, Jean-Claude ULiege

Article for general public (2000)

Carte blanche concernant la vision globale de l'environnement terrestre et son évolution.

Detailed reference viewed: 4 (0 ULiège)