References of "Gérard, Jean-Claude"
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See detailIsolating the 130.4 nm and 135.6 nm emissions in Ganymede’s aurora using broadband optics
Molyneux, Philippa M; Grodent, Denis ULg; Bunce, Emma J et al

Conference (2012, September 27)

We discuss a technique for isolating the two main Far Ultraviolet emission lines in Ganymede’s aurora by adding flight proven transmission filters to a broad- band, wide-field imager design. We find that ... [more ▼]

We discuss a technique for isolating the two main Far Ultraviolet emission lines in Ganymede’s aurora by adding flight proven transmission filters to a broad- band, wide-field imager design. We find that the ra- tio of OI emissions at 135.6 nm and 130.4 nm can be recovered if the transmission of the filters and other optical elements are well known. This ratio allows constraints to be placed on the relative abundances of O atoms and O2 molecules within Ganymede’s at- mosphere, leading to more accurate models of atmo- spheric composition. [less ▲]

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See detailVenus O2 night glow observations with VIRTSI/Venus Express
Migliorin, Alessandra; Piccioni, Giuseppe; Gérard, Jean-Claude ULg et al

Conference (2012, September)

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See detailSPICAM dayglow measurements: a tool to retrieve CO2 vertical density profile and exospheric temperatures
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S. et al

Conference (2012, September)

We analyze the behavior of the CO2+ and CO Cameron ultraviolet dayglow in the atmosphere of Mars through a large dataset of dayside grazing limb observations performed by the Spectroscopy for ... [more ▼]

We analyze the behavior of the CO2+ and CO Cameron ultraviolet dayglow in the atmosphere of Mars through a large dataset of dayside grazing limb observations performed by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) on board the Mars Express spacecraft. Limb profiles are studied to retrieve the temperature of the Martian exosphere and its variability with season, latitude and solar activity. We use a one-dimensional chemical-diffusive model to retrieve the main features of the emissions and constrain the temperature and density vertical profiles of the main components of the Martian atmosphere. [less ▲]

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See detailThe vertical distribution of the Venus NO nightglow: limb profiles inversion and one-dimensional modeling
Stiepen, Arnaud ULg; Soret, Lauriane ULg; Gérard, Jean-Claude ULg et al

in Icarus (2012), 220

Ultraviolet (UV) spectra of the δ (190-240 nm) and γ (225-270 nm) bands of the nitric oxide (NO) molecule have been measured on the nightside of the atmosphere of Venus with the Spectroscopy for ... [more ▼]

Ultraviolet (UV) spectra of the δ (190-240 nm) and γ (225-270 nm) bands of the nitric oxide (NO) molecule have been measured on the nightside of the atmosphere of Venus with the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument on board Venus Express (VEX). Excited NO molecules on the nightside of the planet are created by radiative recombination of O(3P) and N(4S) atoms. The atoms are produced by photodissociation of CO2 and N2 molecules on the dayside and then transported on the nightside by the global circulation. We analyze all nightside limb profiles obtained since 2006 and provide a statistical study of the nitric oxide airglow layer and its variability. We also apply a spatial deconvolution and an Abel inversion method to the limb profiles to retrieve and quantify the volume emission rate distribution and its dependence on several factors. We also show that about 10% of the limb profiles exhibits a secondary peak located above or below the main airglow peak. Furthermore, a one-dimensional chemical-diffusive model is used to simultaneously model the globally averaged NO and O2(a1Δg) airglow vertical distributions using CO2 and O density profiles rooted in VIRTIS and SPICAV observations. We find that a downward flux of 2×10 9 N(4S) atoms cm−2s−1 and a eddy diffusion coefficient equal to 1 x10 11/sqrt(n) cm−2s−1, where n is the total number density, provide the best set of values to parametrize the one-dimensional representation of the complex 3-D dynamical processes. [less ▲]

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See detailConversion from HST ACS and STIS auroral counts into brightness, precipitated power, and radiated power for H2 giant planets
Gustin, Jacques ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2012), 117

The STIS and ACS instruments onboard HST are widely used to study the giant planet's aurora. Several assumptions have to be made to convert the instrumental counts into meaningful physical values (type ... [more ▼]

The STIS and ACS instruments onboard HST are widely used to study the giant planet's aurora. Several assumptions have to be made to convert the instrumental counts into meaningful physical values (type and bandwidth of the filters, definition of the physical units, etc…), but these may significantly differ from one author to another, which makes it difficult to compare the auroral characteristics published in different studies. We present a method to convert the counts obtained in representative ACS and STIS imaging modes/filters used by the auroral scientific community to brightness, precipitated power and radiated power in the ultraviolet (700-1800 Å). Since hydrocarbon absorption may considerably affect the observed auroral emission, the conversion factors are determined for several attenuation levels. Several properties of the auroral emission have been determined: the fraction of the H[SUB]2[/SUB] emission shortward and longward of the HLy-α line is 50.3% and 49.7% respectively, the contribution of HLy-α to the total unabsorbed auroral signal has been set to 9.1% and an input of 1 mW m[SUP]-2[/SUP] produces 10 kR of H[SUB]2[/SUB] in the Lyman and Werner bands. A first application sets the order of magnitude of Saturn's auroral characteristics in the total UV bandwidth to a brightness of 10 kR and an emitted power of ˜2.8 GW. A second application uses published brightnesses of Europa's footprint to determine the current density associated with the Europa auroral spot: 0.21 and 0.045 μA m[SUP]-2[/SUP] assuming no hydrocarbon absorption and a color ratio of 2, respectively. Factors to extend the brightnesses observed with Cassini-UVIS to total H[SUB]2[/SUB] UV brightnesses are also provided. [less ▲]

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See detailInversion of Venus NO nightglow limb profiles
Stiepen, Arnaud ULg; Soret, Lauriane ULg; Gérard, Jean-Claude ULg et al

Conference (2012, July)

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See detailObservations of equatorward patchy auroral ultraviolet emissions
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2012, May 25)

Detailed reference viewed: 29 (16 ULg)
See detailSaturn's temperature profiles at high, medium and low latitudes derived from UVIS occultations
Gustin, Jacques ULg; Moses, Julie; Gérard, Jean-Claude ULg et al

Conference (2012, May 24)

Detailed reference viewed: 23 (10 ULg)
See detailEquatorward auroral features: auroral signatures of injections
Radioti, Aikaterini ULg; Roussos, Elias; Grodent, Denis ULg et al

Scientific conference (2012, May)

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See detailUnderstanding of the Venus upper atmosphere dynamics with O2(a1 ) Venus Express observations
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

Poster (2012, April)

The O2(a1 ) nightglow emission at 1.27 m may be used as a tracer of the dynamics prevailing in the Venusian upper mesosphere. This emission has thus been observed with ground-based telescopes and from ... [more ▼]

The O2(a1 ) nightglow emission at 1.27 m may be used as a tracer of the dynamics prevailing in the Venusian upper mesosphere. This emission has thus been observed with ground-based telescopes and from space with instruments such as VIRTIS on board Venus Express. Observations have shown that the emission maximum is statistically located close to the antisolar point at 96 km. As originally suggested by Connes et al. (1979), such an emission results from the production of oxygen atoms on the Venus dayside by photodissociation and electron impact dissociation of CO2 and CO, which are then transported to the nightside by the subsolar to antisolar general circulation, where they recombine to create excited O2(a1 ) molecules. Their radiative deexcitation produces the O2(a1 ) nightglow with a maximum near the antisolar point. However, VIRTIS observations indicate that the O2(a1 ) nightglow emission is highly variable, both in intensity and location. Actually, when considering individual observations, the patch of bright emission is rarely located at the antisolar point and the brighter area around this point is the result of statics accumulation. Also, when considering several individual observations acquired in a short period of time, it is possible to follow an individual emission patch and to deduce its displacement and its brightness variation due to activation or deactivation. In this study, we analyze several sequences of VIRTIS observations in order to understand the Venus upper mesosphere dynamics.We show that the intensity can vary by several megaRayleighs in a couple of hours with effective lifetimes on the order of several hours. The horizontal motion of the spots leads to the conclusion that winds in the 95-100 km region are in the range of 25 to 150 m s-1, in good agreement with the study by Hueso et al. (2008). [less ▲]

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See detailThe Venus nitric oxide nightglow vertical distribution : update, new features and modelling
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Soret, Lauriane ULg et al

Poster (2012, April)

Ultraviolet (UV) spectra of the delta (190-240 nm) and gamma (225-270 nm) bands of the nitric oxide (NO) molecule have been measured in the atmosphere of the Venus night side with the Spectroscopy for ... [more ▼]

Ultraviolet (UV) spectra of the delta (190-240 nm) and gamma (225-270 nm) bands of the nitric oxide (NO) molecule have been measured in the atmosphere of the Venus night side with the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument on board Venus Express (VEX). Excited NO molecules on the night side of the planet find their source in the radiative recombinaison of O(3P) and N(4S) atoms produced on the dayside by Extreme Ultraviolet (EUV) solar photons that cause photodissociation of CO2 and N2 molecules. We analyse with an improved statistics the behaviour of the vertical emission profile of the NO nightglow. We also present a method used to retrieve and analyse the volume emission rate. We describe the dependence of the vertical distribution with latitude and local time and its variability. New features in the vertical distribution of the NO emission such as double peaks are also exhibited. Furthermore, we use a one-dimensional chemical-diffusive model to compare the major features of the calculated O2 1.27 microm and NO UV emissions profiles with those observed with SPICAV. [less ▲]

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See detailExpansion of the main auroral oval at Jupiter : evidence for Io’s control over the Jovian magnetosphere
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Poster (2012, April)

In spring 2007, New Horizons' Jupiter fly-by provided a unique opportunity for the largest observation campaign dedicated to the Jovian aurora ever carried out by the Hubble Space Telescope. UV images of ... [more ▼]

In spring 2007, New Horizons' Jupiter fly-by provided a unique opportunity for the largest observation campaign dedicated to the Jovian aurora ever carried out by the Hubble Space Telescope. UV images of the aurora have been acquired on a quasi-daily basis from mid-February to mid-June 2007. Polar projection of the auroral emissions clearly show a continuous long-term expansion of main oval additionally to day by day variations. The main oval moved so much that the Ganymede footprint, which is usually located equatorward of the main emissions, has even been observed inside of it. Simultaneously, the occurrence rate of large equatorward isolated auroral features increased over the season. These emission patches are generally attributed to injections of depleted flux tubes. On 6th June, one of these features exceptionally moved down to the Io footpath. The Io footprint seemed to disappear while the footprint moved through this patch of emission. This disappearance is a unique case among all the UV images of the aurora acquired during the last 12 years. We suggest that all these changes seen in the Jovian aurora are evidence for a major reconfiguration of the magnetosphere induced by increased volcanic activity on Io. Indeed, New Horizons observed particularly intense activity from the Tvashtar volcano in late February 2007. Moreover, sodium cloud brightening caused by volcanic outbursts have also been seen in late May 2007. According to our interpretation, repeated volcanic outbursts beefed up the plasma torus density and its mass outflow rate. This caused the corotation breakdown boundary to migrate closer to Jupiter. Consequently, the main auroral oval moved equatorward. As heavy flux tubes move outward, sparsely filled ones should be injected into the inner magnetosphere in order to conserve the magnetic flux in this region. This phenomenon could explain the large number of injection signatures observed in May-June 2007. Such a cloud of depleted flux tubes probably disrupted the Io-magnetosphere interaction, leading to an abnormally faint Io footprint. [less ▲]

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See detailThe oxygen nightglow emissions of Venus: vertical distribution and role of collisional quenching
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Migliorini, Alessandra et al

Conference (2012, April)

The oxygen nightglow emissions of Venus: vertical distribution and role of collisional quenching J.-C. Gérard (1), L. Soret (1), A. Migliorini (2), G. Piccioni (2), and P. Drossart (3) (1) LPAP ... [more ▼]

The oxygen nightglow emissions of Venus: vertical distribution and role of collisional quenching J.-C. Gérard (1), L. Soret (1), A. Migliorini (2), G. Piccioni (2), and P. Drossart (3) (1) LPAP - Université de Liège - Belgium (jc.gerard@ulg.ac.be, 0032 4 366 9711), (2) INAF - Rome, Italy, (3) LESIA, Observatoire de Paris - Meudon, France Three-body recombination of atomic oxygen produces O2 molecules excited in different electronic states such as a 1∆g, b 1 􏰀+g , A 3 􏰀+u , c 1 􏰀uand A’ 3∆u, each with a specific quantum efficiency. When they radiate, optical transitions are observed in a wide range of wavelengths extending from the ultraviolet to the near infrared. In planetary atmospheres, spontaneous radiative deexcitation compete with collisional quenching with ambient molecules and atoms. As a consequence, the corresponding airglow emission profiles may significantly differ from each other in brightness and altitude of the emitting layer. We model the volume emission rates and limb profiles of the O2 Atmospheric Infrared (a 1∆-X 3 􏰀), Herzberg I (A 3 􏰀-X 3 􏰀), Herzberg II (c 1 􏰀-X 3 􏰀), Chamberlain (A’ 3∆-a 1∆) bands expected on the Venus night side. The quenching rates are taken from laboratory and observational planetary data and we apply two different methods to determine the oxygen and CO2 density profiles. One is based on recent analysis of data collected by instruments on board the Venus Express mission. The second one uses a one-dimensional chemical-diffusive model where the free parameters are the strength of turbulent transport and the downward flux of O atoms. Both approaches indicate that the calculated intensities of each transition range over several orders of magnitude and that differences are expected in the altitude of the maximum emission. These predictions will be compared with VIRTIS/Venus Express limb observations, which make it possible to derive the vertical distribution of the O2 emissions in the visible and infrared. These measurements suggest that no difference is observed between the altitude of the peak of the IR Atmospheric and Herzberg II bands. Conclusions will be drawn about the validity of the current set of quenching coefficients used in the model. [less ▲]

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