References of "Gérard, Jean-Claude"
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See detailSolar Wind Interaction with the Magnetosphere of Jupiter : Impact on the Magnetopause and the Aurorae
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, November 20)

The outcome of the interaction between the solar wind and the Jovian magnetic field bears many differences compared to the Earth's case. At Earth, the solar wind is the major particle and energy source in ... [more ▼]

The outcome of the interaction between the solar wind and the Jovian magnetic field bears many differences compared to the Earth's case. At Earth, the solar wind is the major particle and energy source in the magnetosphere. At Jupiter, the tremendous volcanism on the moon Io is the main plasma source and Jupiter's rapid rotation (relative to its size) is the main energy source for the particles populating its magnetosphere. Combined with a weaker solar wind pressure and a larger Alfvén Mach number as the distance from the Sun increases, all these parameters modify the relative importance of large scale Dungey reconnection and viscous interaction at the magnetopause. In order to study these differences, here we present a statistical analysis of magnetopause waves and flux tube event on the Jovian magnetopause, based on in-situ measurement from the spacecraft that flew-by or orbited around Jupiter. Moreover, variations of the solar wind have significant impact on the Jovian magnetospheric current systems and such changes reflect on the aurora. In this presentation, we will also review the recent findings concerning the aurora at Jupiter and their relationship with the solar wind. [less ▲]

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See detailJupiter's equatorward auroral features : Possible signature of magnetospheric injections
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2014, September)

We investigate the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images obtained in 2000-2007. Several properties ... [more ▼]

We investigate the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images obtained in 2000-2007. Several properties of the auroral emissions are analyzed. 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. Finally, we discuss the processes causing auroral signatures of injections. This comparative study demonstrates that the structures under study are most probably related to magnetospheric injections and sheds light to the mechanism involved in the magnetosphere-ionosphere dynamics. [less ▲]

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See detailIsolating auroral FUV emission lines using compact, broadband instrumentation
Molyneux, P.M.; Bannister, N.P.; Bunce, E.J. et al

in Planetary and Space Science (2014), 103

Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region ... [more ▼]

Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region is low, allowing both dayside and nightside auroras to be imaged simultaneously. The ratio of intensities between certain FUV emission lines or regions can be used to characterise the precipitating particles responsible for auroral emissions, and hence is a useful diagnostic of magnetospheric dynamics. Here, we describe how the addition of simple transmission filters to a compact broadband imager design allows far ultraviolet emission ratios to be deduced while also providing large-scale instantaneous images of the aurora. The low mass and volume of such an instrument would make it well-suited for both small satellite Earth-orbiting missions and larger outer planet missions from which it could be used to characterise the tenuous atmospheres observed at several moons, as well as studying the auroral emissions of the gas giants. We present a study to investigate the accuracy of a technique to allow emission line ratio retrieval, as applied to the OI 130.4 nm and 135.6 nm emissions at Ganymede. The ratio of these emissions provides information about the atmospheric composition, specifically the relative abundances of O and O2. Using modelled FUV spectra representative of Ganymede's atmosphere, based on observations by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), we find that the accuracy of the retrieved ratios is a function of the magnitude of the ratio, with the best measurements corresponding to a ratio of ∼1.3 . [less ▲]

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See detailSpectral mapping of the FUV Jovian aurora and electron energy distribution
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2014, September)

Observations have been made with the Hubble Space Telescope in the timetag mode using the STIS long slit. During the 40 min of the observations, the slit spatially scanned the polar regions to build ... [more ▼]

Observations have been made with the Hubble Space Telescope in the timetag mode using the STIS long slit. During the 40 min of the observations, the slit spatially scanned the polar regions to build spectral maps of the jovian aurora. The emission is composed of the HI Lyman-alpha line and the H2 Lyman and Werner bands. The shorter wavelengths are partly absorbed by the methane layer overlying the bulk of the auroral emission. Since the CH4 absorption cross section drastically drops above 140 nm, the longer wavelengths are not absorbed and the intensity directly reflects the precipitated energy flux carried by the electrons. Maps of the intensity ratio of the two spectral regions will be presented, together with the associated auroral electron energy. These values will be compared with those expected from current magnetosphere-ionosphere model. They will provide input into 3-D modeling of the auroral heat source into the high-latitude Jovian upper atmosphere. [less ▲]

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See detailSaturn’s elusive nightside polar arc
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2014)

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See detailCassini Ultraviolet Images of Saturn's Aurorae
Pryor, Wayne; Jouchoux, Alain; Esposito, Larry et al

Scientific conference (2014, August 04)

Cassini has been obtaining auroral images and spectra of Saturn with the Ultraviolet Imaging Spectrograph (UVIS). We will present highlights of the auroral images, showing a variety of morphologies ... [more ▼]

Cassini has been obtaining auroral images and spectra of Saturn with the Ultraviolet Imaging Spectrograph (UVIS). We will present highlights of the auroral images, showing a variety of morphologies, including multiple arcs, spiral forms, polar cusp activity, and rotating emission features, some of them pulsating with a roughly 1-hour period. A satellite footprint of Enceladus is occasionally visible. [less ▲]

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See detailDiurnal thermosphere scale height from MEX/SPICAM grazing limb data
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S et al

Conference (2014, July 01)

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See detailConstraints on the summer-to-winter transport from SPICAM/MEX nitric oxide observations
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Gagné, M.-E. et al

Conference (2014, July 01)

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See detailDynamic auroral storms on Saturn as observed by the Hubble Space Telescope
Nichols, J. D.; Badman, S. V.; Baines, K. H. et al

in Geophysical Research Letters (2014), 41

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission ... [more ▼]

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ˜330% rigid corotation from near ˜01 h LT toward ˜08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current. [less ▲]

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See detailQuasi-periodic flares in Jupiter's aurora : new results
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, April 29)

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode ... [more ▼]

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode of the Space Telescope Imaging Spectrograph (STIS), a high time resolution mode which allows to observe temporal variations on timescales of tens of seconds. In the present study, we focus on sudden and spectacular bursts of auroral emissions taking place in the active region located poleward of the main emissions and called “flares”. A previous study, based on only two image sequences acquired with rather unfavorable viewing angles, showed that these flares could reappear quasi-periodically on time scales of 2-3 minutes. Phenomena with similar timescales have been identified by in-situ spacecraft in relativistic electron and radio data as well as in reconnection signatures, for example. But the physical mechanism behind these ubiquitous signatures remains to be unveiled. Here we make use of the most recent and much larger data set to study in further details the occurrence rate, the period, the location, the extent and the motion of these quasi-periodic flares and to compare their behavior in both hemispheres. Quantifying these parameters allows us to narrow down the possibilities among likely explanations and provide a tentative scenario for these short timescale quasi-periodic features. [less ▲]

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See detailSaturn’s elusive transpolar arc
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, April)

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See detailTime variations of O2(a1Delta) nightglow spots on the Venus nightside and dynamics of the upper mesosphere
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

in Icarus (2014), 237

The dynamical regime of the Venus upper atmosphere is mainly decomposed into three regions. The first one, located below 65 km of altitude is governed by the retrograde superrotational zonal (RSZ ... [more ▼]

The dynamical regime of the Venus upper atmosphere is mainly decomposed into three regions. The first one, located below 65 km of altitude is governed by the retrograde superrotational zonal (RSZ) circulation. The second region above 130 km is dominated by the subsolar to antisolar (SS–AS) circulation. The dynamics of the transition region in between are still not fully understood. However, the O2(a1D) nightglow emission at 1.27 lm, whose emitting layer is located at 96 km, can be used as a tracer of the dynamics in this transition region and the imaging spectrometer VIRTIS-M on board Venus Express, orbiting Venus since April 2006, acquired a large amount of nadir observations at this wavelength. Several previous studies showed that the O2(a1D) nightglow emission is statistically located near the antisolar point. In this study, individual VIRTIS-M nadir observations have been analyzed to investigate the variability of the phenomenon. Bright patches of 1.27 lm airglow have been extracted from every observation. It appears that the location of the bright patch is highly variable, even though the brightest patches occur near the antisolar point. Nadir observations have also been divided into time series, allowing generating animations to follow the intensity and the displacement of bright patches over time. Apparent wind velocities and characteristic decay/rise times and have been deduced from these time series. The speed of the displacements varies from 0 up to 213 m s 1, with a mean value of 54 m s 1. Owing to the high variability of the direction of the displacements both in the short and the long terms, no clear trend of a global motion at 96 km can be deduced from these observations. The mean decay time is 750 min while the mean rise time is 1550 min. The decay time can be explained as a combination of radiative decay and atomic oxygen transport. [less ▲]

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See detailLatitudinal structure of the Venus O2 infrared airglow: A signature of small-scale dynamical processes in the upper atmosphere
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Piccioni, Giuseppe et al

in Icarus (2014), 236

Images of the nightside limb of Venus have been obtained in the northern hemisphere with the VIRTIS multispectral infrared imager on board Venus Express between April 2006 and October 2008. We analyze the ... [more ▼]

Images of the nightside limb of Venus have been obtained in the northern hemisphere with the VIRTIS multispectral infrared imager on board Venus Express between April 2006 and October 2008. We analyze the latitudinal distribution of the O2(a1D) airglow limb profiles at 1.27 lm to characterize its distribution and variability. We show that the instantaneous structure of the emission is very different from the statistical global view of an enhanced emission near the equator, decreasing in brightness and slightly increasing in altitude toward the poles. The peak intensity of the limb profiles varies by a factor up to 50 between the brightest spots and the darkest regions. The bright airglow spots correspond to regions of enhanced downward flow of oxygen atoms originating from the dayside. Considerable variations in brightness and morphology are observed in the altitude–latitudinal distribution over a 24-h period. Analysis of the limb profiles indicates that secondary airglow peaks located at altitudes higher than the mean value of 96 km are observed on about 30% of the latitudinal cuts, but they are concentrated in narrow latitude areas extending over a few hundred kilometers. Most of them occur in transition regions between two altitude regimes in the 50 to 60 N region, possibly associated with the drop of the cloud top altitude observed equatorward of the ‘‘cold collar’’. We interpret these results as an indication that the strength of vertical transport in this mesosphere–thermosphere transition region is very variable both in location and time. This variability, also observed in nadir airglow images and wind measurements, is a key characteristic of the mesosphere–thermosphere transition region. It may be caused by fluctuations of the global day-to-night circulation generated by gravity waves. We show with a one dimensional model that local enhancements of eddy transport is a possibility. This variability is currently not accounted for by global circulation models that predict a single stable region of enhanced airglow in the vicinity of the antisolar point. [less ▲]

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See detailThe Ultraviolet Spectrograph on NASA’s Juno Mission
Gladstone, G Randal; Persyn, Steven C.; Eterno, John S. et al

in Space Science Reviews (2014)

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These ... [more ▼]

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These observations will be coordinated and correlated with those from Juno’s other remote sensing instruments and used to place in situ measurements made by Juno’s particles and fields instruments into a global context, relating the local data with events occurring in more distant regions of Jupiter’s magnetosphere. Juno-UVS is based on a series of imaging FUV spectrographs currently in flight—the two Alice instruments on the Rosetta and New Horizons missions, and the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter mission. However, Juno-UVS has several important modifications, including (1) a scan mirror (for targeting specific auroral features), (2) extensive shielding (for mitigation of electronics and data quality degradation by energetic particles), and (3) a cross delay line microchannel plate detector (for both faster photon counting and improved spatial resolution). This paper describes the science objectives, design, and initial performance of the Juno-UVS. [less ▲]

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See detailDynamics of the aurora at Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, February 19)

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See detailOpen flux in Saturn's magnetosphere
Badman, Sarah; Jackman, Caitriuna; Nichols, Jonathan et al

in Icarus (2014), 231

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See detailThe 2-3 minutes periodicity in the polar aurora and the magnetosphere of Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Poster (2013, December 10)

The main aurora at Jupiter is related to the middle magnetosphere and the corotation breakdown of the magnetospheric plasma. On the other hand, the polar regions either magnetically map to the outer ... [more ▼]

The main aurora at Jupiter is related to the middle magnetosphere and the corotation breakdown of the magnetospheric plasma. On the other hand, the polar regions either magnetically map to the outer magnetosphere or correspond to field lines open to the interplanetary medium and most of the auroral emissions from this region are still poorly understood. Among these polar auroral emissions are the flares, dramatic brightenings of several million square kilometers over a couple of minutes. Two previously reported observations of the southern hemisphere showed that these flares can be quasi-periodic with a re-occurrence time of 2-3 minutes. Here we report results from the Hubble Space Telescope campaign carried out in 2012-2013 with the STIS FUV instrument in time-tag mode (PI: D. Grodent). This campaign consisted in alternating observations of the two hemispheres. Based on the analysis of this dataset, we confirm that these quasi-periodic flares are ubiquitous and occur in both hemispheres. Moreover, in at least one case, these flares appear to occur in phase in both hemispheres. We compare the characteristics of these flares with those of the relativistic electron bursts observed by the Ulysses spacecraft with the HET instrument. We find that 2-3 minutes quasi-periodic burst are much more frequent than previously reported and that they magnetically map to the same auroral area as the flares. We conclude that these two phenomena are most probably related and arise from a common origin. [less ▲]

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See detailSaturn’s UV aurora: the (high latitude) point of view of Cassini
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gustin, Jacques ULg et al

Conference (2013, December 09)

The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of ... [more ▼]

The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of the associated particles and magnetic field. Cassini’s T83 flyby of Titan 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. We will give an overview of the auroral emissions observed so far with the UVIS camera on board Cassini. In particular we will link the morphology of the aurora with specific 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. Moreover, this presentation will focus on small-scale features, which can only be observed by an instrument close enough to the planet. We will also present movies of these observations, allowing us to explore the auroral dynamics at various timescales. This information will be used to identify the various mechanisms at play in Saturn’s magnetosphere. [less ▲]

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See detailEvolution of the Io Footprint Brightness II: Modeling
Hess, Sébastien; Bonfond, Bertrand ULg; Chantry, Virginie ULg et al

in Planetary and Space Science (2013), 88

The interaction of Io with the Jovian magnetosphere creates the best known and brightest satellite-controlled aurorae in our solar system. These aurorae are generated by the precipitation of electrons ... [more ▼]

The interaction of Io with the Jovian magnetosphere creates the best known and brightest satellite-controlled aurorae in our solar system. These aurorae are generated by the precipitation of electrons, which are accelerated by the Alfvén waves carrying the current between the satellite and the planet. A recent study computed the energy deposited on top of Jupiter's ionosphere due to the electron precipitation and retrieved the correct mean brightness of Io-related aurorae. The model developed in this study takes into account the acceleration mechanism and the Alfvén wave propagation effects. We use the same method to investigate the brightness variation of the different components of the Io footprint as a function of longitude. These observations are discussed in a companion paper. We identify several effects that act together to modulate the footprint brightness such as Alfvén wave reflections, magnetic mirroring of the electrons, the local interaction at Io and kinetic effects close to Jupiter. We identify the effects contributing the most to the modulation of the brightnesses of the three brightest components of the Io footprints: the main and reflected Alfvén wing spots and the transhemispheric electron spot. We show in particular that the modulation of the efficiency of the electron acceleration can be of greater importance than the modulation of the power generated at Io. We reproduce the average modulation of the spot brightnesses and present an extensive discussion of possible explanations for the observed features not reproduced by our model. [less ▲]

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