References of "Gérard, Jean-Claude"
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See detailEvolution of the Io footprint brightness I: Far-UV observations
Bonfond, Bertrand ULg; Hess, Sébastien; Gérard, Jean-Claude ULg et al

in Planetary and Space Science (2013), 88

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the ... [more ▼]

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the brightness and precipitated power for each individual spot, using the image database gathered from 1997 to 2009 with the Hubble Space Telescope in the Far-UV domain. We show that the relative brightness of the spots varies with the System III longitude of Io. Moreover, our novel measurement method based on 3D simulations of the auroral features allows to derive the precipitated energy fluxes from images on which the emission region is observed at a slant angle. Peak values as high as 2 W/m² are observed for the main spot, probably triggering a localized and sudden heating of the atmosphere. Additionally, strong brightness differences are observed from one hemisphere to another. This result indicates that the location of Io in the plasma torus is not the only parameter to control the brightness, but that the magnetic field asymmetries also play a key role. Finally, we present new data confirming that significant variations of the spots' brightness on timescales of 2-4 minutes are ubiquitous, which suggests a relationship with intermittent double layers close to Jovian surface. [less ▲]

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See detailThe multiple spots of the Ganymede auroral footprint
Bonfond, Bertrand ULg; Hess, Sébastien; Bagenal, Fran et al

in Geophysical Research Letters (2013), 40

The interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere, called the satellite footprints. So far, footprints have ... [more ▼]

The interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere, called the satellite footprints. So far, footprints have been detected for Io, Europa, Ganymede, and Enceladus. These footprints are usually seen as single spots. However, the Io footprint, the brightest one, displays a much more complex morphology made of at least three different spots and an extended tail. Here we present Hubble Space Telescope FUV images showing evidence for a second spot in the Ganymede footprint. The spots separation distance changes as Ganymede moves latitudinally in the plasma sheet, as is seen for the Io footprint. This indicates that the processes identified at Io are universal. Moreover, for similar Ganymede System III longitudes, the distance may also vary significantly with time, indicating changes in the plasma sheet density. We identified a rapid evolution of this distance 8 days after the detection of a volcanic outburst at Io, suggesting that such auroral observations could be used to estimate the plasma density variations at Ganymede. [less ▲]

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See detailCassini UVIS Saturn Auroral Images from the 2013 HST/Cassini Campaign
Pryor, Wayne; Jouchoux, Alain; Esposito, Larry et al

Conference (2013, October)

In 2013 coordinated observations of Saturn by the Cassini spacecraft and Hubble Space Telescope (HST) were obtained. During these observations the Cassini spacecraft provided a high-latitude view of ... [more ▼]

In 2013 coordinated observations of Saturn by the Cassini spacecraft and Hubble Space Telescope (HST) were obtained. During these observations the Cassini spacecraft provided a high-latitude view of Saturn's auroras. Intense auroras were observed by the Ultraviolet Imaging Spectrograph (UVIS) from close range (about 5 Saturn radii away). A 6-frame UVIS movie has been constructed from some of the observations from May 20- 21, 2013 showing the evolution of two bright auroral features. We report on the UVIS images, the corresponding spectra, and compare the UVIS data to HST images and data from other Cassini instruments. [less ▲]

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See detailMartian thermospheric temperatures retrieved from SPICAM dayglow measurements
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Montmessin, Franck et al

Poster (2013, October)

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See detailHubble observations of Jupiter’s north–south conjugate ultraviolet aurora
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

in Icarus (2013), 226

Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a ... [more ▼]

Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a statistical basis or were not obtained with high sensitivity and resolution. Such observations are important to discriminate between different mechanisms responsible for the electron acceleration of the different components of the aurora such as the satellite footprints, the «main oval» or the polar emissions. The field of view of the ACS and STIS cameras on board HST is not wide enough to provide images of the full jovian disk. We thus compare the morphology of the north and south aurora observed 55 min apart and we point out similarities and differences. On one occasion HST pointed successively the two polar regions and auroral images were seen separated by only 3 min. This makes it possible to compare the emission structure and the emitted FUV power of corresponding regions. We find that most morphological features identified in one hemisphere have a conjugate counterpart in the other hemisphere. However, the power associated with conjugate regions of the main oval, diffuse or discrete equatoward emission observed quasi-simultaneously may be different in the two hemispheres. It is not directly nor inversely proportional to the strength of the B-field as one might expect for diffuse precipitation or field-aligned acceleration with equal ionospheric electron density in both hemispheres. Finally, the lack of symmetry of some polar emissions suggests that some of them could be located on open magnetic field lines. [less ▲]

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See detailThe Ganymede auroral footprint: implications of the spots’ multiplicity
Bonfond, Bertrand ULg; Hess, Sébastien; Bagenal, Fran et al

Conference (2013, September 10)

We report here the finding of a secondary spot for the Ganymede auroral footprint on Jupiter. Moreover, we characterize the evolution of the Ganymede footprint morphology with longitude and time. Finally ... [more ▼]

We report here the finding of a secondary spot for the Ganymede auroral footprint on Jupiter. Moreover, we characterize the evolution of the Ganymede footprint morphology with longitude and time. Finally, we discuss the implications of these results with respect to the morphology of the other satellite footprints. [less ▲]

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See detailMars thermospheric temperatures retrieved from SPICAM dayglow measurements
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S et al

Conference (2013, September 10)

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See detailCassini’s recent high inclination views of Saturn’s UV aurorae
Grodent, Denis ULg; Gustin, Jacques ULg; Radioti, Aikaterini ULg et al

Conference (2013, September)

On 22 May 2012, Cassini flew by Titan at a closest approach distance of 955 km. This T83 flyby significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined ... [more ▼]

On 22 May 2012, Cassini flew by Titan at a closest approach distance of 955 km. This T83 flyby significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined phase 1 which will last until March 16, 2015. During this 3-year period, the inclination of Cassini’s orbit reaches very high values, up to 62° in April 2013. This makes it possible to obtain exceptionally good views of Saturn’s poles to observe the auroral emissions in different wavelength ranges. In this presentation, we will summarize the auroral observations taken in the UV with the UVIS camera. We will focus on the morphology of the emission and pinpoint signatures that are attributed to various magnetospheric processes, such as dayside reconnection and auroral bifurcations, nightside reconnection, hot plasma injections. We will also take advantage of the view from nearly above the poles to describe the overall shape and size of the aurora, which are expected to respond to the solar wind conditions. This set of data is to be compared with the contemporaneous observations obtained from the different remote and in situ instruments onboard Cassini. It will also be completed by quasi- simultaneous UV observations of the northern aurorae caught by HST in April 2013 and may allow inter hemispheric comparisons. This information will be used to constrain the various processes at play in Saturn’s magnetosphere. [less ▲]

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See detailComparative analysis of airglow emissions in terrestrial planets, observed with VIRTIS-M instruments on board Rosetta and Venus Express
Migliorini, A.; Piccioni, G.; Capaccioni, F. et al

in Icarus (2013), 226

Airglow emissions are optimal processes to investigate the chemistry and dynamics in planetary atmospheres. In this study, we focus on the O2 and OH airglow emissions in Venus, Earth, and Mars atmospheres ... [more ▼]

Airglow emissions are optimal processes to investigate the chemistry and dynamics in planetary atmospheres. In this study, we focus on the O2 and OH airglow emissions in Venus, Earth, and Mars atmospheres, which are controlled by chemical reactions common to the three planets. By studying these phenomena on Venus, Earth, and Mars using similar instruments, we are able to derive information about their photochemistry and the physical conditions of the atmospheres, but also to constrain the dynamics responsible for transport of atomic oxygen, ozone and other minor species. After a review of the nightglow emissions observed in the Venus atmosphere, we analyze the O2 and OH airglow emissions in the Earth's atmosphere observed during the 3 swing-bys of our planet by the Rosetta spacecraft. We also report the detection of the O2 nightglow emission in the Mars atmosphere, observed in February 2007 during the Rosetta fly-by of the planet. The airglow characteristics are in agreement with the measurements obtained from sensors on board Mars Express. [less ▲]

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See detailThe Ganymede aurora …
Gérard, Jean-Claude ULg; Shematovich, Valery; Bisikalo, Dmitry et al

Poster (2013, September)

In this Report we present the Monte Carlo model for calculation of oxygen UV and IR emissions due to the electron precipitation in the Ganymede polar regions. These techniques will provide column ... [more ▼]

In this Report we present the Monte Carlo model for calculation of oxygen UV and IR emissions due to the electron precipitation in the Ganymede polar regions. These techniques will provide column densities of atmospheric species at better than or equal to 1 km spatial resolution, and will constrain the amount of some specific compounds from limb scans and during stellar occultation. This investigation also needs characterization of the vertical temperature profile from ground up to about 400 km altitude with ~5 km vertical resolution as well as mapping of water vapour concentration. This can be performed by multiple water line observations in the 200-600 μm wavelength range. It shall be complemented by ion and neutral mass spectrometry of plasma particles, radio occultations to measure structures of the neutral atmosphere and ionosphere, and plasma wave measurements to constrain plasma density and temperature of the ionosphere. [less ▲]

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See detailIsolated transient UV auroral structures at Jupiter: possible signatures of magnetospheric injections 
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2013, July 11)

We investigate transient ultraviolet auroral features located equatorward of the main emission (130 features) based on Hubble Space Telescope (HST) observations of the northern and southern Jovian ... [more ▼]

We investigate transient ultraviolet auroral features located equatorward of the main emission (130 features) based on Hubble Space Telescope (HST) observations of the northern and southern Jovian hemispheres (2000-2007). Several properties of the auroral emissions are analyzed, such as their position in auroral region, power and brightness. Additionally, we magnetically map the auroral structures to the equatorial plane using VIPAL model and we compare their observed properties with those of magnetospheric injections observed by Galileo. We suggest that these transient auroral structures could be related to magnetospheric injections. The mapped radial position and system III longitude of the observed auroral features are in good agreement with those of the injections observed in the equatorial plane by Galileo. Based on power and brightness of the auroral features, we discuss the mechanisms involved in the ionosphere-magnetosphere coupling injections. This comparative study demonstrates that the structures under study are related to magnetospheric injections and sheds light to the mechanism involved in the magnetosphere-ionosphere dynamics. [less ▲]

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See detailVariability of the Jovian aurorae: focus on a selection of recent results
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2013, July 11)

The aurorae at Jupiter can be separated into four main components: the satellite footprints, the outer emissions, the main emissions and the polar emissions. Each of these components displays some form of ... [more ▼]

The aurorae at Jupiter can be separated into four main components: the satellite footprints, the outer emissions, the main emissions and the polar emissions. Each of these components displays some form of variability in location, brightness and/or shape. The nature and the timescale of these changes is particularly revealing of the processes at play. The footprints of Io and Ganymede are often made of several spots. The distance between these spots and their brightness essentially varies as the planetary magnetic dipole rotates relative to the moons and as the plasma torus or plasma sheet wobble across the satellite orbital plane. However, the spots brightness can also considerably vary on a timescale of minutes as well as from one year to another. The outer emissions are made of diffuse, patchy or arc-shaped emissions. Two different sources have been proposed to explain these features: injections of hot plasma from the outer magnetosphere and the pitch angle scattering boundary. These features usually last for a few Jovian rotations, but their occurrence rate appears to be related to the global dynamics of the inner magnetosphere on timescales of months. The main emissions sometimes appear as a complete oval, but they usually have a more chaotic appearance, with broken arcs, gaps and forks. Their brightness and morphology respond to changes in the solar wind characteristics. Nevertheless, the dawn portion of the main emissions sometimes displays spectacular brightening apparently unrelated to the solar wind: the dawn storms. Moreover, on timescales of several months, the statistical location of the main emissions also evolves as the material input from Io increases or decreases. Globally speaking, the polar emissions also respond to the solar wind input. However, the term “polar emissions” encompasses many different auroral features obviously driven from different mechanisms. Spots and arcs, located just inside the main emissions on the dawn and night side and lasting for a few tens of minutes, have been seen to re-occur every 2 to 3 days. They have thus been associated with night-side reconnection related to the Vasyliũnas cycle. On the other hand, the dusk-side of the polar region is the locus of quasi-periodic UV flares on timescales of 2 to 3 minutes, while periodicities of 20 to 45 minutes have been identified for their X-ray counterpart. The central part of the polar region is very dynamic, with patches of emissions constantly appearing, moving and disappearing within minutes. However, along with these patches, elongated auroral arcs dubbed “polar auroral filaments” may remain present for several consecutive days. As we will see in this review talk, the current data set of UV images from the Hubble Space Telescope, including the brand new time-tag sequences from the latest 2012-2013 campaign, gives access to a wide range of auroral phenomena that only begin to reveal their secrets. [less ▲]

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See detailJupiter’s elusive bald patch
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gustin, Jacques ULg et al

Conference (2013, July)

The detailed morphology of Jupiter’s UV auroral emissions is definitely very complex. To some extent, this complexity depicts the zoo of processes taking place inside, and sometimes, outside Jupiter’s ... [more ▼]

The detailed morphology of Jupiter’s UV auroral emissions is definitely very complex. To some extent, this complexity depicts the zoo of processes taking place inside, and sometimes, outside Jupiter’s enormous magnetosphere. One is naturally more inclined to focus on the bright emissions, but recent progresses in cosmology teach us that there is also important information in the darkness. In this present, preliminary study, we are exploring a dark region of Jupiter’s polar aurora -“Jupiter’s bald patch”- located poleward of the main emission (oval). It appears to be bordered by patchy features belonging to auroral regions often referred to as the swirl and flare regions. These regions contain the poleward most auroral features. Therefore, it is legitimate to ask whether this dark region, even closer to the pole, is actually the polar cap, implying some level of reconnection of Jupiter’s strong magnetic field with the interplanetary magnetic field. An ongoing HST campaign is providing stunning high temporal and spatial (and spectral) resolution time tagged images of Jupiter’s northern and southern aurora. They show that the bald patch is conspicuous on some images but much less obvious in others. They also suggest that it is not always completely devoid of emission, possibly alluding to a weak, intermittent, Dungey-like cycle. [less ▲]

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See detailJupiter's conjugate ultraviolet aurora
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2013, July)

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See detailThe time evolution of O2(a1Δ) individual observations acquired by VIRTIS-M on board Venus Express
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

Poster (2013, June 10)

The O2(a1Δ) nightglow emission at 1.27 µm may be used as a tracer of the Venus upper mesosphere dynamics. This emission has been observed with VIRTIS-M-IR on board Venus Express. Previous studies showed ... [more ▼]

The O2(a1Δ) nightglow emission at 1.27 µm may be used as a tracer of the Venus upper mesosphere dynamics. This emission has been observed with VIRTIS-M-IR on board Venus Express. Previous studies showed that the emission maximum is statistically located close to the antisolar point at ∼96 km. This airglow 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 metastable O2(a1Δ) molecules. Their radiative deexcitation produces the O2(a1Δ) nightglow with a maximum near the antisolar point. However, VIRTIS individual observations indicate that the O2(a1Δ) nightglow emission is highly variable, both in intensity and location. Individual observations acquired every hour during a short period of time can also be grouped sequentially. Bright emission patches can thus be tracked and both their displacement and intensity variations can be analyzed. The peak intensity can vary from 1 to 6 megaRayleighs. We show that the emission peak moves with a mean value of ~80 m s-1, in good agreement with an earlier study by Hueso et al. (2008). The velocity vector in intensity and direction is evaluated approximately every 40 min. These displacements are highly variable, but some dynamical characteristics can be deduced from the observations. These results will be compared with other results of velocity determination in the upper mesosphere. [less ▲]

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See detailDynamics of the auroral bifurcations at Saturn and their role in magnetopause reconnection
Gérard, Jean-Claude ULg; Radioti, Aikaterini ULg; Grodent, Denis ULg

Conference (2013, June)

We summarize recent results obtained with the UVIS instrument on board Cassini. They demonstrate that auroral signatures of magnetic field reconnection events in the flanks of the magnetopause are ... [more ▼]

We summarize recent results obtained with the UVIS instrument on board Cassini. They demonstrate that auroral signatures of magnetic field reconnection events in the flanks of the magnetopause are observed in the UV images collected by UVIS. [less ▲]

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See detailVenus night side measurements of winds at 115 km altitude from NO bright patches tracking.
Bertaux, J.-L.; Gérard, Jean-Claude ULg; Stiepen, Arnaud ULg et al

Conference (2013, June)

N and O atoms produced by photo-dissociation of CO2 and N2 on the day side of Venus are transported to the night side in the thermospheric circulation. When the air parcel is descending, the recombination ... [more ▼]

N and O atoms produced by photo-dissociation of CO2 and N2 on the day side of Venus are transported to the night side in the thermospheric circulation. When the air parcel is descending, the recombination N+O→ NO produces the famous γ and δ bands of NO emission. Pioneer Venus (1978) suggested that the statistical center of the emission is off from the anti-solar point, about one- two hours in Local time after midnight. This is confirmed from SPICAV/VEX results, and the explanation generally accepted is the influence of retrograde super rotation. However, the emission takes place at 115 km, while VIRTIS/VEX, with maps of O2 emission (peak altitude 95 km) in the night side of Venus (recombination of O+O coming from the day side), has shown that the maximum of emission is statistically centered on the antisolar point. Therefore, there is no influence of super-rotation at 95 km. One way to explain this paradox is that the cause of the super rotation is different at 115 km and in the lower atmosphere. Alternately, some gravity waves could propagate from below, crossing the altitude 95 km with minimal interaction, and breaking around 115, depositing their momentum. Another consideration is that the altitude of N2 photo-dissociation is higher in the thermosphere than CO2, therefore the thermospheric circulation pattern may be different for the transport of N atoms, and O atoms. We have started building maps of the NO emission by moving around the spacecraft along its orbit on the night side. The idea is that NO emission is concentrated generally in rather well defined patches of light. Therefore, by comparing maps taken at 1 hour or 24 hr interval, we can make a “bright patch tracking”, and derive directly the velocity of the moving air parcel containing N and O (we are aware that a part of the motion could be due to a phase shift of a gravity wave, if it has some influence on the NO emission). Preliminary results from this exercise with Venus Express will be presented and discussed. [less ▲]

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