References of "Gérard, Jean-Claude"
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See detailDiscovery and characterization of an ozone layer in Venus’atmosphere
Montmessin, F.; Bertaux, J.-L.; Lefèvre, F. et al

Conference (2011)

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See detailAtomic oxygen distributions in the Venus thermosphere: Comparisons between Venus Express observations and global model simulations
Brecht, A.; Bougher, S. W.; Gérard, Jean-Claude ULg et al

in Icarus: International Journal of Solar System Studies (2011)

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See detailNightside reconnection at Jupiter: Auroral and magnetic field observations from 26 July 1998
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2011), 116

In this study we present ultraviolet and infrared auroral data from 26 July 1998, and we show the presence of transient auroral polar spots observed throughout the postdusk to predawn local time sector ... [more ▼]

In this study we present ultraviolet and infrared auroral data from 26 July 1998, and we show the presence of transient auroral polar spots observed throughout the postdusk to predawn local time sector. The polar dawn spots, which are transient polar features observed in the dawn sector poleward of the main emission, were previously associated with the inward moving flow resulting from tail reconnection. In the present study we suggest that nightside spots, which are polar features observed close to the midnight sector, are related to inward moving flow, like the polar dawn spots. We base our conclusions on the near-simultaneous set of Hubble Space Telescope (HST) and Galileo observations of 26 July 1998, during which HST observed a nightside spot magnetically mapped close to the location of an inward moving flow detected by Galileo on the same day. We derive the emitted power from magnetic field measurements along the observed plasma flow bubble, and we show that it matches the emitted power inferred from HST. Additionally, this study reports for the first time a bright polar spot in the infrared, which could be a possible signature of tail reconnection. The spot appears within an interval of 30 min from the ultraviolet, poleward of the main emission on the ionosphere and in the postdusk sector planetward of the tail reconnection x line on the equatorial plane. Finally, the present work demonstrates that ionospheric signatures of flow bursts released during tail reconnection are instantaneously detected over a wide local time sector. [less ▲]

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See detailThe auroral footprint of Enceladus on Saturn
Pryor, Wayne R; Rymer, Abigail M; Mitchell, Donald G et al

in Nature (2011), 472

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between ... [more ▼]

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. [less ▲]

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See detailNightglow investigation around 1.27 µm with VIRTIS/Venus-Express
Migliorini, A.; Piccioni, G.; Gérard, Jean-Claude ULg et al

Conference (2010, December)

In this study we report about the investigation of the spectral region 1.22-1.32 µm of the night side of Venus, observed by the VIRTIS instrument (Visible and InfraRed Spectral Imaging Spectrometer) on ... [more ▼]

In this study we report about the investigation of the spectral region 1.22-1.32 µm of the night side of Venus, observed by the VIRTIS instrument (Visible and InfraRed Spectral Imaging Spectrometer) on board the Venus Express spacecraft. This spectral region is characterized by the presence of the extensively studied (a1Δg – X3Σg-) (0,0) O2 nightglow band, the most intense emission observed on the night side of Venus. However, the comparison between data and synthetic spectra from the (0,0) band only, lacks a good match at wavelengths longer than 1.27 μm, especially in the region around 1.28-1.29 μm. The effects of temperature, CO2 and the (8,5) OH emission at 1.28 µm were investigated as a possible cause to the spectral disagreement, but they all are not enough to explain the observed difference. Instrumental effects were also excluded as possible cause of the mismatch. We found that the inclusion of the (1,1) band O2 emission in the synthetic spectra, originating from the upper vibrational level ν=1 of the (a1Δg – X3Σg-) transition centered at 1.28 μm, in addition to the (0,0), significantly improves the agreement between simulated spectra and observed data in the region at 1.28-1.29 μm. A synthetic spectrum, including the (0,0) and the (1,1) is produced and compared to 4 observed VIRTIS spectra, as an example. From the analyzed data, it results that the (1,1) band with an intensity ranging from the 8 to 15% of the (0,0) band is required to best reproduce the observed VIRTIS spectra. This corresponds to a (1,1) band intensity equal to 3.1-5.8 MR, in limb view, in agreement with the upper limit set by Connes et al., (1979), on their ground-based observations of the oxygen nightglow of Venus. [less ▲]

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See detailTwo-dimensional time-dependent model of the transport of minor species in the Venus night side upper atmosphere
Collet, Arnaud ULg; Cox, Cédric ULg; Gérard, Jean-Claude ULg

in Planetary and Space Science (2010), 58

We present a numerical tool developed to quantify the role of processes controlling the spatio-temporal distribution of the NO ultraviolet and O2 infrared nightglows in the Venus night side upper ... [more ▼]

We present a numerical tool developed to quantify the role of processes controlling the spatio-temporal distribution of the NO ultraviolet and O2 infrared nightglows in the Venus night side upper atmosphere, observed with the VIRTIS and SPICAV instruments on board Venus Express. This numerical tool consists in a two-dimensional chemical-transport time-dependent model which computes in a hypothetical rectangular solving domain the spatio-temporal distributions of the number densities of the four minor species at play in these two nightglow emissions. The coupled nonlinear system of the four partial differential equations, describing the spatio-temporal variations of the minorspecies, has been solved using a finite volume method with a forward Euler method for the time integration scheme. As an application, we have first simulated a time-constant supply of atoms through the upper boundary of the solving domain. The fluxes are inhomogeneous relative to its horizontal direction, in order to simulate regions of enhanced downward flow of oxygen and nitrogen giving rise to NO and O2 brightening. Given that these two emissions show large time variations, we have also simulated a time-dependent downward flux of O and N atoms. It results from these simulations that the lack of correlation between the NO and O2 nightglows largely result from to the coupling between horizontal and vertical transport processes and the very different chemical lifetimes of the two species. In particular,we have quantified the role of each process generating spatio-temporal de-correlations between the NO and O2 nightglows. [less ▲]

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See detailDiscovery of pulsed polar flares in the Jovian aurorae
Bonfond, Bertrand ULg; Vogt, M~F; Grodent, Denis ULg et al

Poster (2010, December)

The most active part of the aurora at Jupiter is certainly the polar region, i.e. the emissions located poleward of the main auroral oval. This region is known to occasionally show localized but dramatic ... [more ▼]

The most active part of the aurora at Jupiter is certainly the polar region, i.e. the emissions located poleward of the main auroral oval. This region is known to occasionally show localized but dramatic enhancements of its brightness, referred to as polar flares. These emissions have been associated with the polar cusp, based on their location in the polar cap. In summer 2009, right after the refurbishment of the Space Telescope Imaging Spectrograph camera, the Hubble Space Telescope acquired the longest high-time resolution sequence ever of images of the Jovian aurora. We report the first observations of a quasi-periodicity in the occurrence of these flares, with a timescale of ~2-3 minutes. By using a magnetic flux mapping model, we show that these features originate from a region located at a radial distance ranging from 80 to 100 Jovian radii and local times between 10:00 and 15:00. As a consequence, by analogy with similar behaviors observed in the Earth aurora, we suggest that these emissions could be attributed to pulsed reconnections in the dayside magnetopause. [less ▲]

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See detailThe Juno Mission
Bolton, S. J.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

in Barbieri, Cesare; Coradini, Marcello; Chakrabarti, Supriya (Eds.) et al Proceedings IAU Symposium No. 269. "Galileo's Medicean Moons: their impact on 400 years of discovery" (2010, November 03)

Juno is the next NASA New Frontiers mission which will launch in August 2011. The mission is a solar powered spacecraft scheduled to arrive at Jupiter in 2016 and be placed into polar orbit around Jupiter ... [more ▼]

Juno is the next NASA New Frontiers mission which will launch in August 2011. The mission is a solar powered spacecraft scheduled to arrive at Jupiter in 2016 and be placed into polar orbit around Jupiter. The goal of the Juno mission is to explore the origin and evolution of the planet Jupiter. Juno's science themes include (1) origin, (2) interior structure, (3) atmospheric composition and dynamics, and (4) polar magnetosphere and aurora. A total of nine instruments on-board provide specific measurements designed to investigate Juno's science themes. The primary objective of investigating the origin of Jupiter includes 1) determine Jupiter's internal mass distribution by measuring gravity with Doppler tracking, 2) determine the nature of its internal dynamo by measuring its magnetic fields with a magnetometer, and 3) determine the deep composition (in particular the global water abundance) and dynamics of the sub-cloud atmosphere around Jupiter, by measuring its thermal microwave emission. [less ▲]

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See detailElectron-atmosphere interaction in the aurora of giant planets
Gérard, Jean-Claude ULg

Conference (2010, October 18)

All methods converge to indicate that the efficiency of the H2 (B,C states) emission is close to 10 kR/mW m-2 of electron precipitation. The UV aurora is a direct instantaneous map of the distribution of ... [more ▼]

All methods converge to indicate that the efficiency of the H2 (B,C states) emission is close to 10 kR/mW m-2 of electron precipitation. The UV aurora is a direct instantaneous map of the distribution of the electron precipitation. By contrast, the IR H3+ aurora is indirectly produced and its intensity depends on the amount of H3+ ions and the local temperature. It has the advantage to be observable from the ground The «UV color ratio » method is a powerful tool to probe the electron mean energy IF the distribution of HCs (mostly methane) is known EUV spectroscopy is very useful to determine the depth of the electron energy deposition, but so far, without spatial resolution [less ▲]

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See detailThe distributions of the OH (Δv=1) and (Δv=2) emissions on the Venus nightside
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

Conference (2010, September)

The presence of OH was detected in the spectrum of the Venus mesosphere observed at the limb with the VIRTIS instrument on board the Venus Express spacecraft [3]. The (1-0) and (2-1) transitions at 2.80 ... [more ▼]

The presence of OH was detected in the spectrum of the Venus mesosphere observed at the limb with the VIRTIS instrument on board the Venus Express spacecraft [3]. The (1-0) and (2-1) transitions at 2.80 and 2.94 mm, respectively and the (2-0) band at 1.43 mm were clearly identified. The results of this study show that a correlation is observed between the emissions associated to the Δv=1 and the Δv=2 sequences. [less ▲]

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See detailThe Venus oxygen nightglow and density distributions
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Montmessin, Franck et al

Conference (2010, September)

Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atmosphere. Results deduced from observations can be implemented to produce a data model of Venus atmosphere ... [more ▼]

Observing Venus nightglow is a key tool to understand the composition and the dynamics of its atmosphere. Results deduced from observations can be implemented to produce a data model of Venus atmosphere. For instance, the Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft is very useful to analyze the O2(a1Δ) nightglow at 1.27 µm in the Venus mesosphere. Nadir observations can be used to create a statistical map of the emission on Venus nightside. It appears that the maximum of the emission is located near the antisolar point. Limb observations also provide information on the altitude and on the shape of the emission layer. Combining nadir observations and vertically integrated limb observations improves the statistics of the emission map on Venus nightside. An associated limb profile can also be deduced for any point of the nightside. Given all these O2(a1Δ) intensity profiles, O2* density profiles can be calculated. O density profiles can also be calculated as long as CO2 density profiles are available. These can be retrieved either from the VTS3 model or from SPICAV stellar occultation measurements. Finally, three-dimensional maps of excited molecular and atomic oxygen densities can be generated. The oxygen density map shows significant differences from the VTS3 model predictions. [less ▲]

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See detailJupiter's ultraviolet polar emission: a statistical study
Coumans, Valérie ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2010, September)

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See detailThe NO Venus nightglow: SPICAV observations and implications on transport in the lower thermosphere
Gérard, Jean-Claude ULg; Cox, Cédric ULg; Bertaux, J.-L.

Conference (2010, June 22)

A new set of 725 NO limb profiles has been analyzed. The profiles have been deconvolved and inverted to get volume emission rates. Updates mean VER peak altitude is 115 km, in excellent agreement with PV ... [more ▼]

A new set of 725 NO limb profiles has been analyzed. The profiles have been deconvolved and inverted to get volume emission rates. Updates mean VER peak altitude is 115 km, in excellent agreement with PV results obtained 30 years ago. The corresponding average vertical intensity is 1.2 kR. The altitude of emission occurs at a higher altitude near the bright spot region than at larger distances (by about 7 km). The location of the statistical bright spot is the same as observed with PV (that is shifted dawnward by 2 hrs and slightly south of AS point). The nightside mean vertical intensity is between 0.4 and 1.8 kR, which brackets the values derived from the limb profiles. These results, coupled with other airglow measurements, provide constraints on global atmospheric circulation and vertical transport [less ▲]

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See detailSaturn's polar auroral emissions
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010, June 07)

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See detailSaturn's aurora seen by HST and UVIS
Grodent, Denis ULg; Radioti, Aikaterini ULg; Bonfond, Bertrand ULg et al

Conference (2010, June 07)

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See detailThe Venus OH Nightglow Distribution
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

Poster (2010, June)

The first identification of the OH airglow in the terrestrial mesosphere was made in 1950 by Meinel [1950]. Recently, the unexpected presence of the OH nightglow was observed in the Venus mesosphere by ... [more ▼]

The first identification of the OH airglow in the terrestrial mesosphere was made in 1950 by Meinel [1950]. Recently, the unexpected presence of the OH nightglow was observed in the Venus mesosphere by Piccioni et al. [2008] using a limb profile from the Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft. They clearly identified the (1-0) and (2-1) transitions at 2.80 and 2.94 µm, respectively and the (2-0) band at 1.43 µm. Additional bands belonging to the Δv=1 sequence also appear to be present longward of the (1-0) band. In a preliminary study of characteristics of the OH emission distribution, Gérard et al. [2010] pointed out a correlation between the OH(Δv=1) and the O2(a1Δ) nightglow intensities. In Soret et al. [2010], the full dataset of VIRTIS-M limb observations of the OH Venus nightglow has been corrected from the thermal emission of the planet and analyzed to determine its characteristics. Based on 3328 limb profiles, the study shows that the emission is highly variable. No clear dependence of the airglow layer altitude versus the antisolar angle is established. The peak brightness appears to decrease away from the antisolar point even if the variability at a given location is very strong. Some correlation between simultaneous observations of the intensity of the OH and the O2(a1∆) emissions has also been detected, presumably because atomic oxygen is a common precursor to the formation of O2(a1∆) and O3, whose reaction with H produces excited OH. A relation given in the one-dimensional photochemical model of Krasnopolsky [2009] has been used to link the OH and the O2(a1∆) airglows through the hydrogen flux at 130 km. It appeared that using a constant flux did not fill well the simultaneous OH and O2 observations. Either the flux has to vary with the distance to the antisolar point or other dimensions have to be involved. [less ▲]

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See detailA Far-UV Imager for the Jupiter Ganymede Orbiter
Bunce, E. J.; Molyneux, P.; Bannister, N. et al

Poster (2010, May 17)

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See detailAuroral footprints; everywhere
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2010, May 06)

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and ... [more ▼]

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and the Jovian magnetosphere causes strong Alfvénic perturbations which propagate along the magnetic field lines. On their way towards Jupiter’s polar regions, these perturbations accelerate charged particles which then interact with Jupiter’s ionosphere where they loose a fraction of their energy in the form of auroral emissions. Each of the three moons leaves an auroral footprint around the poles of Jupiter which departs from the bulk of the auroral emission. Their location is mainly controlled by the topology of the field lines and thus analysis of the auroral footprints provides information on the magnetic field itself. In that regard, the satellites auroral footpaths were used to highlight the presence of a strong magnetic anomaly in the northern hemisphere of Jupiter. Detailed inspection of the footprints’ brightness and morphology as a function of time reveals fundamental information on the interaction mechanisms near the moons, on the particles acceleration mechanisms as well as on the Jovian ionosphere. For example, it was suggested that the Io footprint actually consists of several spots resulting from successive steps in the perturbation propagation process. Another example is the finding of three different timescales in the variations of Ganymede’s footprint; each of them is pointing to a different part of the electromagnetic interaction between the moon’s mini-magnetosphere and the Jovian plasma. Several recent images of Saturn’s auroral regions obtained with Cassini/UVIS at high latitude show an obvious auroral spot at the predicted location of Enceladus’ footprint. This major finding demonstrates that the electromagnetic interaction between a moon and its parent planet is not unique to Jupiter but appears to be a common feature in planetary systems. [less ▲]

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