References of "Gérard, Jean-Claude"
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See detailDoes Saturn's UV aurora vary with SKR phase?
Nichols, J. D.; Cowley, S. W. H.; Clarke, J. T. et al

Conference (2009, July 27)

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See detailSaturn's equinoctial auroras
Nichols, J. D.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2009, July 27)

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See detailThe morphology of equatorial electron beams at Io
Jacobsen, S.; Saur, J.; Neubauer, F. M. et al

Conference (2009, July 27)

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See detailSaturn Auroral Images and Movies from Cassini UVIS
Pryor, W. R.; Grodent, Denis ULg; Gérard, Jean-Claude ULg

Conference (2009, July 27)

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See detailThe auroral footprint of Ganymede
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114(A07212),

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede ... [more ▼]

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede footprint. Based on an analysis of ultraviolet images obtained with the Hubble Space Telescope we demonstrate that the auroral footprint surface matches a circular region in Ganymede's orbital plane having a diameter of 8 to 20 RG. Temporal analysis of the auroral power of Ganymede's footprint reveals variations of different timescales: 1) a 5 hours timescale associated with the periodic flapping of Jupiter's plasma sheet over Ganymede, 2) a 10 to 40 minutes timescale possibly associated with energetic magnetospheric events, such as plasma injections, and 3) a 100 s timescale corresponding to quasi-periodic fluctuations which might relate to bursty reconnections on Ganymede's magnetopause and/or to the recurrent presence of acceleration structures above Jupiter's atmosphere. These three temporal components produce an auroral power emitted at Ganymede's footprint of the order of ~0.2 GW to ~1.5 GW. [less ▲]

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See detailThe Io UV footprint: Location, inter-spot distances and tail vertical extent
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by ... [more ▼]

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by an auroral curtain, called the tail, extending more than 90° longitude in the direction of planetary rotation. We use recent Hubble Space Telescope images of Jupiter to analyze the location of the footprint spots and tail as a function of Io's location in the jovian magnetic field. We present here a new IFP reference contour---the locus of all possible IFP positions---with an unprecedented accuracy, especially in previously poorly covered sectors. We also demonstrate that the lead angle - the longitudinal shift between Io and the actual IFP position - is not a reliable quantity for validation of the interaction models. Instead, the evolution of the inter-spot distances appears to be a better diagnosis of the Io-Jupiter interaction. Moreover, we present observations of the tail vertical profiles as seen above the limb. The emission peak altitude is ~900 km and remains relatively constant with the distance from the main spot. The altitudinal extent of the vertical emission profiles is not compatible with precipitation of a mono-energetic electron population. The best fit is obtained for a kappa distribution with a characteristic energy of ~70 eV and a spectral index of 2.3. The broadness of the inferred electron energy spectrum gives insight into the physics of the electron acceleration mechanism at play above the IFP tail. [less ▲]

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See detailVariation of different components of Jupiter's auroral emission
Nichols, J. D.; Clarke, J. T.; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114

The Hubble Space Telescope (HST) data set obtained over two campaigns in 2007 is used to determine the long-term variability of the different components of Jupiter's auroras. Three regions on the planet's ... [more ▼]

The Hubble Space Telescope (HST) data set obtained over two campaigns in 2007 is used to determine the long-term variability of the different components of Jupiter's auroras. Three regions on the planet's disc are defined: the main oval, the low-latitude auroras, and the high-latitude auroras. The UV auroral power emitted from these regions is extracted and compared to estimated solar wind conditions projected to Jupiter's orbit from Earth. In the first campaign the emitted power originated mainly from the main oval and the high-latitude regions, and in the second campaign the high-latitude and main oval auroras were dimmer and less variable, while the low-latitude region exhibited bright, patchy emission. We show that, apart from during specific enhancement events, the power emitted from the poleward auroras is generally uncorrelated with that of the main oval. The exception events are dawn storms and compression region enhancements. It is shown that the former events, typically associated with intense dawnside main oval auroras, also result in the brightening of the high-latitude auroras. The latter events associated with compression regions exhibit a particular auroral morphology; that is, where it is narrow and well defined, the main oval is bright and located ~1° poleward of its previous location, and elsewhere it is faint. Instead there is bright emission in the poleward region in the postnoon sector where distinct, bright, sometimes multiple arcs form. [less ▲]

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See detailVenus express: Highlights of the nominal mission
Titov, D. V.; Svedhem, H.; Taylor, F. W. et al

in Solar System Research (2009), 43

Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit ... [more ▼]

Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit. The payload consists of seven experiments. It includes a powerful suite of remote sensing imagers and spectrometers, instruments for in-situ investigation of the circumplanetary plasma and magnetic field, and a radio science experiment. The spacecraft, based on the Mars Express bus modified for the conditions at Venus, provides a versatile platform for nadir and limb observations as well as solar, stellar, and radio occultations. In April 2006 Venus Express was inserted in an elliptical polar orbit around Venus, with a pericentre height of Ë 250 km and apocentre distance of Ë 66000 km and an orbital period of 24 hours. The nominal mission lasted from June 4, 2006 till October 2, 2007, which corresponds to about two Venus sidereal days. Here we present an overview of the main results of the nominal mission, based on a set of papers recently published in Nature, Icarus, Planetary and Space Science, and Geophysical Research Letters. [less ▲]

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See detailCorrection to ``Equatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations''
Radioti, Aikaterini ULg; Tomás, Ana Tomas; Grodent, Denis ULg et al

in Geophysical Research Letters (2009), 36

<A href="/journals/gl/gl0909/2009GL038676/">Abstract Available</A> from <A href="http://www.agu.org">http://www.agu.org</A>

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See detailResponse of Jupiter's and Saturn's auroral activity to the solar wind
Clarke, J. T.; Nichols, J.; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114

While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, there is considerable evidence that auroral emissions on Jupiter and ... [more ▼]

While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, there is considerable evidence that auroral emissions on Jupiter and Saturn are driven primarily by internal processes, with the main energy source being the planets' rapid rotation. Prior observations have suggested there might be some influence of the solar wind on Jupiter's aurorae and indicated that auroral storms on Saturn can occur at times of solar wind pressure increases. To investigate in detail the dependence of auroral processes on solar wind conditions, a large campaign of observations of these planets has been undertaken using the Hubble Space Telescope, in association with measurements from planetary spacecraft and solar wind conditions both propagated from 1 AU and measured near each planet. The data indicate a brightening of both the auroral emissions and Saturn kilometric radiation at Saturn close in time to the arrival of solar wind shocks and pressure increases, consistent with a direct physical relationship between Saturnian auroral processes and solar wind conditions. At Jupiter the correlation is less strong, with increases in total auroral power seen near the arrival of solar wind forward shocks but little increase observed near reverse shocks. In addition, auroral dawn storms have been observed when there was little change in solar wind conditions. The data are consistent with some solar wind influence on some Jovian auroral processes, while the auroral activity also varies independently of the solar wind. This extensive data set will serve to constrain theoretical models for the interaction of the solar wind with the magnetospheres of Jupiter and Saturn. [less ▲]

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See detailLatitudinal and local time distribution of the O2 infrared nightglow and O density in the lower thermosphere
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Saglam, Adem et al

Poster (2009, May)

Atomic oxygen is the major component in the Earth’s upper thermosphere. The O density reaches a maximum of about 3x1010 cm-3 near 100 km. The 1.27 µm emission of the IR Atmospheric bands generated by ... [more ▼]

Atomic oxygen is the major component in the Earth’s upper thermosphere. The O density reaches a maximum of about 3x1010 cm-3 near 100 km. The 1.27 µm emission of the IR Atmospheric bands generated by recombination of O atoms has been observed in the nightglow. On the night side, the O2 airglow peaks at ~95 km with a value of ~10 MR. <br />Atomic oxygen is present in the Martian atmos-phere but that the intensities values are below the cur-rent instrument detectability threshold. The Mars at-mosphere oxygen density is highly variable, depending on the altitude, temperature, latitude and longitude. <br />On Venus, atomic oxygen has been measured in situ only above 145 km on both the day and the night sides. Limb observations obtained with the Venus In-frared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express show that the O2 infrared nightglow peaks at ~97 km, with a mean intensity val-ue of about 1,3 MR [1, 2]. Yet, the distribution is largely inhomogeneous, with an enhanced region of ~3 MR statistically located near the midnight meridian at low latitude [3]. The oxygen density can be mapped using the O2 airglow and CO2 density vertical distribu-tions [4]. The O2 volume emission rates are obtained with an Abel inversion of the O2 limb profiles and CO2 vertical distributions are taken from the Venus International Reference Atmosphere (VIRA) model. The results show that the O density peak is located between 93 and 105 km (with a mean value of 104 km) and ranges from 2.8x1010 to 8.5x1011 cm-3 (with a mean value of 2.2x1011 cm-3). No correlations between the peak altitude and the latitude or the peak altitude and the local time are observed. However, the O density decreases and its variability increases while moving away from the antisolar point. [less ▲]

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See detailComparison of O2 IR and NO UV night airglow variations on Mars and Venus
Brecht; Bougher, S. W.; Gérard, Jean-Claude ULg et al

Conference (2009, May)

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See detailAirglow and aurora
Gérard, Jean-Claude ULg

Conference (2009, May)

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See detailThe ultraviolet nitric oxide emission in the nightside atmospheres of Venus and Mars
Cox, Cédric ULg; Gérard, Jean-Claude ULg; Bertaux, J. L.

Conference (2009, May)

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See detailThe location and topology of electron beams in Io‘s wake
Jacobsen, Sven; Saur, Joachim; Neubauer, Friz et al

Conference (2009, April 22)

The Galileo spacecraft measured hot field aligned electron beams near Io during three flybys. We apply our 3D MHD model of the Io-Jupiter interaction to constrain the location and shape of field aligned ... [more ▼]

The Galileo spacecraft measured hot field aligned electron beams near Io during three flybys. We apply our 3D MHD model of the Io-Jupiter interaction to constrain the location and shape of field aligned electron beams for the individual flyby scenarios. Io continuously generates MHD waves by disturbing the Jovian magnetoplasma. Currents carried by Alfvén waves propagate predominantly along the magnetic field lines. The waves accelerate electrons as the number of charge carriers decreases on their way to Jupiter. These energetic electrons precipitate into the Jovian ionosphere, visible as prominent Io footprint emission in the Jovian aurora. On the other hand electrons have to be accelerated upward to form the beams measured by Galileo. Unlike the beam formation, the position and spatial structure of these beams has been poorly discussed. We adopt our 3D MHD model initial conditions to the individual flyby scenario and determine the spatial morphol- ogy of beams in Io’s orbital plane. We compare our findings to Galileo observations and find very good agreement. Moreover, we use our model to further investigate in detail a recent concept which involves cross-hemisphere electron beams to explain certain auroral features of the Io footprint emission such as a leading spot and secondary spots [Bonfond et al., 2008]. Our results indicate that besides geometrical properties, such as Io’s position in the torus, the incoming plasma density controls the travel path and topology of an electron beam. [less ▲]

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See detailEquatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations
Radioti, Aikaterini ULg; Tomás, Ana Teresa; Grodent, Denis ULg et al

in Geophysical Research Letters (2009), 36

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes ... [more ▼]

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes in the electron pitch angle distribution between the inner and middle magnetosphere (PAD boundary), indicative of electron diffusion. This region, magnetically maps to the equatorward diffuse emissions on both hemispheres. Whistler mode waves, observed simultaneously, can scatter electrons into the loss cone and lead to electron precipitation in the ionosphere. Based on simultaneous HST FUV and Galileo wave and electron data we test the conditions for electron scattering by whistler mode waves and derive the energy flux precipitated in the ionosphere. The comparison of the derived precipitation energy flux with the observed auroral brightness indicates that the energy contained in the PAD boundary can account for the auroral emissions. [less ▲]

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See detailObservations of Jovian polar auroral filaments
Nichols, J. D.; Clarke, J. T.; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2009), 36

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ... [more ▼]

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ~100 kR spanning the highly variable region poleward of the main oval. This observation, made using Hubble Space Telescope images, is significant since no coherent structures have previously been observed in Jupiter's very high latitude auroral region, and it may help shed light on the dynamics of Jupiter's under-explored magnetotail. PAFs have been observed in 4 sets of observations over 6 days in 2007, and their occurrence appears to be independent of impinging solar wind conditions. The feature comprises two components: the section toward noon remains fixed in orientation toward the sun, while the anti-sunward section rotates. We estimate overall rotation rates of ~0--45% of corotation, values which may indicate the rotation rate of Jupiter's polar ionosphere and tail lobes. [less ▲]

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See detailHydroxyl nightglow on Venus observed by VIRTIS on Venus-Express
Migliorini, A.; Piccioni, G.; Gérard, Jean-Claude ULg et al

Conference (2009, April)

Hydroxyl has been recently observed for the first time in the Venus atmosphere with the VIRTIS spectrometer on board the Venus-Express spacecraft. The (1-0) around 2.81 microns and the (2-0) around 1.46 ... [more ▼]

Hydroxyl has been recently observed for the first time in the Venus atmosphere with the VIRTIS spectrometer on board the Venus-Express spacecraft. The (1-0) around 2.81 microns and the (2-0) around 1.46 microns transitions have been detected. The intensity of the two emissions are respectively about 55 and 480 times less intense than the (0-0) oxygen transition (Piccioni et al, A&A, 2008). The possible chemical reactions which can produce hydroxyl on Venus involve O3 and HO2, with the former being the most probable, and hence OH can be used to indirectly infer the ozone distribution on Venus. VIRTIS data in limb mode observation were analyzed to derive the mean distribution of hydroxyl in the night side of Venus and the results are presented here. The typical peak altitude of the two emissions is set at 95-96 km in limb view, a few km lower than the oxygen emission at 1.27 um due to the transition (0-0). The peak altitude of the latter typically occurs at 97-98 km height. The OH full width at half maximum is in average about 7 km, and sometimes higher. The mean map of (1-0) hydroxyl distribution around 2.81 microns shows a maximum of emission of about 130 kR at about 1h local time. The study of the (2-0) hydroxyl distribution at around 1.46 microns results more difficult due to its weak intensity. [less ▲]

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See detailTransient auroral features at Saturn: Signatures of energetic particle injections in the magnetosphere
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114

We report for the first time transient isolated auroral spots at Saturn's southern polar region, based on Hubble Space Telescope (HST) FUV images. The spots last several minutes and appear distinct from ... [more ▼]

We report for the first time transient isolated auroral spots at Saturn's southern polar region, based on Hubble Space Telescope (HST) FUV images. The spots last several minutes and appear distinct from the rest of the auroral emissions. We study two sets of HST and Cassini observations during which Cassini instrumentation detected signatures of energetic particle injections close to the region where, on the same day, HST observed transient auroral spots. On the basis of the simultaneous remote and in situ observations, we discuss the possibility that the transient features are associated with the dynamical processes taking place in the Kronian magnetosphere. Given the limitations in the available observations, we suggest the following possible explanations for the transient aurora. The injection region could directly be coupled to Saturn's ionosphere by pitch angle diffusion and electron scattering by whistler waves, or by the electric current flowing along the boundary of the injected cloud. The energy contained in the injection region indicates that electron scattering could account for the transient aurora process. [less ▲]

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