References of "Grodent, Denis"
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See detailJupiter's Aurora
Clarke, John T.; Grodent, Denis ULg; Cowley, Stan S. W. et al

in Bagenal, Fran; Dowling, Timothy; McKinnon, William (Eds.) Jupiter : The Planet, Satellites and Magnetosphere (2004)

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See detailThe morphology of Saturn's ultraviolet auroral oval and its time variations
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Clarke, J. T.

Conference (2004)

Global images of the FUV auroral emission surrounding Saturn's south pole have been obtained with Space Telescope Imaging Spectrograph (STIS) since 1998. During this period, the planet's tilt offered a ... [more ▼]

Global images of the FUV auroral emission surrounding Saturn's south pole have been obtained with Space Telescope Imaging Spectrograph (STIS) since 1998. During this period, the planet's tilt offered a nearly complete view of the south auroral oval. Several tens of images were obtained in January 2004, concurrent with in situ measurements of the solar wind parameters made with instruments on board the Cassini probe. This unique set of auroral images includes time-tagged exposures providing information on fast time variations. A subset of collected images is used to define a quiet reference oval. This oval serves a framework to investigate local time and longitudinal variations of brightness and latitudinal motions of the oval, including variation of its radius. Occasionally, the oval is not closed, or reduces to a bright spot apparently as a consequence of enhanced solar wind pressure pulses reaching the front of the magnetosphere. Comparisons with terrestrial counterpart indicate that auroral substorms are not observed on the nightside oval. Instead, some features are seen to rotate with the planet as in the Jovian aurora. These characteristics will be compared with predictions of recent models describing the global current system coupling the magnetosphere and the ionosphere. In particular, the latitude of the oval, departure from corotation and the longitudinal brightness distribution can be used to test the paradigm that the main auroral oval maps to a region of enhanced field-aligned current and to improve current models. [less ▲]

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See detailJupiter's main auroral oval observed with HST-STIS
Grodent, Denis ULg; Clarke, J. T.; Kim, J. et al

in Journal of Geophysical Research. Space Physics (2003), 108(A11),

An extended series of FUV images obtained on 7 days during winter 2000-2001, with fixed pointing, yielded highly accurate tracking of emisson features as Jupiter rotated. They provided newly detailed ... [more ▼]

An extended series of FUV images obtained on 7 days during winter 2000-2001, with fixed pointing, yielded highly accurate tracking of emisson features as Jupiter rotated. They provided newly detailed measurements of the degree of corotation of auroral emissions and their variations with changing central meridian longitude. This 2-month data set provides a statistical average location of the auroral emission and leads to the definition of new "reference ovals.'' The overall auroral morphology pattern is shown to be fixed in System-III longitude and unchanged over a 5-year period. When arranged in central meridian longitude ranges, the images show a significant contraction of the northern main oval as the central meridian longitude increases from 115 to 255degrees. The main auroral oval brightness is globally very stable in comparison with its terrestrial counterpart. It is shown to vary with magnetic local time, increasing from noon to dusk and then decreasing again in the magnetic evening. Hectometric emissions observed simultaneously with Galileo and Cassini reveal interplanetary shocks propagating outward from the Sun which may be related to the contraction of the main auroral oval observed in the HST images taken on 14 December 2000. In addition, we find that a brightening and a significant contraction of the main oval observed on 13 January 2001 corresponded to a time of increased solar wind dynamic pressure. [less ▲]

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See detailJupiter's polar auroral emissions
Grodent, Denis ULg; Clarke, J. T.; Waite, J. H. et al

in Journal of Geophysical Research. Space Physics (2003), 108(A10),

[1] This paper reports a study of Jupiter's polar auroral emissions observed in an extended series of FUV images. They were obtained on seven days, during winter 2000-2001, with the STIS camera on board ... [more ▼]

[1] This paper reports a study of Jupiter's polar auroral emissions observed in an extended series of FUV images. They were obtained on seven days, during winter 2000-2001, with the STIS camera on board the Hubble Space Telescope. The fixed pointing yielded highly accurate and consistent tracking of emisson features as Jupiter rotated, allowing the analysis of the auroral morphology and brightness on timescales ranging from seconds to days. In the Northern Hemisphere, the polar emissions, located poleward of the main oval, usually represent about 30% of the total auroral FUV emitted power. They show emission bursts lasting similar to100 s, while the main oval remains stable. The polar region may be divided into three regions apparently fixed in magnetic local time: the dawnside dark region, the poleward swirl region, and the duskside active region in which flares and arc-like features are observed. Each of these UV emission regions can be identified with its infrared counterpart and probably relates to a different sector of the Dungey cycle or Vasyliunas cycle plasma flows. [less ▲]

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See detailSpectral observations of transient features in the FUV Jovian polar aurora
Gérard, Jean-Claude ULg; Gustin, Jacques ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2003), 108

Images of the Jovian FUV aurora show several morphologically and dynamically different regions. The main oval is usually fairly steady while the high-latitude emission inside the oval can vary over ... [more ▼]

Images of the Jovian FUV aurora show several morphologically and dynamically different regions. The main oval is usually fairly steady while the high-latitude emission inside the oval can vary over timescales of <1 min. We describe time and spatially resolved spectral observations of the Jovian aurora made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Time-tagged spectra have been used to determine variations of the amount of hydrocarbon absorption above the auroral source layer. Rapid brightenings are observed in the high-latitude emission with typical lengths of 50-100 s. They generally are not correlated with enhancements of the main oval in the same longitude sector, indicating decoupled source regions in the magnetosphere. The location of the high-latitude spots and their variability suggest that, unlike the main auroral oval, the polar cap brightenings are connected to short-term variations of the solar wind parameters. Results from a two-stream electron transport model are used to convert observed spectral color ratios into mean electron energies <E>. Electron energies during these brightenings typically range from 40 to 120 keV, close to the values found in the main oval. The time evolution of <E> generally shows little correlation or anticorrelation with the energy flux precipitated during these transient events. This feature suggests that the mechanism responsible for rapid transient brightenings does not increase the energy of the precipitated electrons, but it enhances their number flux. Pitch angle scattering into the loss cone by magnetic pumping of energy perpendicular to the field lines following magnetic field compression is a possible process. [less ▲]

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See detailA new FUV auroral feature on Jupiter
Grodent, Denis ULg; Gladstone, G. R.; Gérard, Jean-Claude ULg et al

Conference (2003, April 01)

In December 2000, a series of HST/STIS FUV images of Jupiter's north auroral region displayed bright transient spots located near local midnight. In the images taken at CML Ë 220[SUP]o[/SUP] the spots ... [more ▼]

In December 2000, a series of HST/STIS FUV images of Jupiter's north auroral region displayed bright transient spots located near local midnight. In the images taken at CML Ë 220[SUP]o[/SUP] the spots (one or two) appear near the limb, poleward and equatorward of the main auroral oval, at latitude Ë 73[SUP]o[/SUP] and λ[SUB]III[/SUB] longitude Ë 145[SUP]o[/SUP]. The dimensions of each spot are very small, about 1[SUP]o[/SUP] in latitude and 5[SUP]o[/SUP] in longitude, which is about the size of the footprint of the Io satellite. However, the analysis of the position of the Galilean satellites and of known small-bodies (comets, asteroids) shows that these spots are not magnetically associated with any of these objects. The emitted power of the spots is variable and can reach several GW (more than the power emitted at the Io footprint). The lightcurves derived from multiple images are consistent with spots disappearing behind the planetary limb as the planet rotates. In addition, one short time-tagged image undoubtedly shows a bright double--spot feature pulsating with a period of 300 s. According to the VIP4 magnetic model, the auroral spots map along field lines down to the jovian magnetosphere in a small region roughly located near midnight at distances larger than 60~R_J. At these distances, a 1[SUP]o[/SUP] by 5[SUP]o[/SUP] auroral spot subtends an equatorial region smaller than 10~R_J by 10~R_J . Consequently, the auroral spots cannot be directly associated with large scale process involving the whole magnetotail but rather with localized events. [less ▲]

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See detailCassini UVIS and HST STIS Time-Resolved Jupiter Auroral Data Compared to QP Radio Bursts
Pryor, W.; Hospodarsky, G.; Stewart, I. et al

Poster (2003)

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Jupiter in a 4-sec integration "high time-resolution mode" on Jan 8, 13-14, and 20-21 in 2001. In this mode Extreme-Ultraviolet and Far ... [more ▼]

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Jupiter in a 4-sec integration "high time-resolution mode" on Jan 8, 13-14, and 20-21 in 2001. In this mode Extreme-Ultraviolet and Far-Ultraviolet spectra were obtained with reduced spectral and spatial resolution in order to study rapid variations in H2 band and H Lyman alpha emission. Previous work has shown that the region inside Jupiter's main auroral ovals contains highly variable spots of emission (auroral flares) that persist for typically 1 or 2 minutes. This duration is similar to that in Jupiter's quasi-periodic (QP) radio bursts. We compare UVIS data to simultaneous Galileo Plasma Wave Subsystem (PWS) and Cassini Radio and Plasma Wave Subsystem (RPWS) observations. Jan 8 was an active period for UV variability, that we associate with polar auroral flares. There is a correlation between the radio and UV bursts in this period, suggesting that they are related phenomena. We will also explore coordinated Hubble Space Telescope Imaging Spectrograph (STIS) time-tagged UV images from Dec 14 and Dec 16, 2000, and Jan 13-14, and Jan 20-21, 2001 to study the spatial properties of the auroral flares. The auroral emissions inside the main oval were most prominent in the Dec 14, 2000 HST data. We acknowledge support from the Cassini Project, the Space Telescope Science Institute, and the NASA OSS Minority University Initiative. [less ▲]

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See detailPreliminary Results from Recent Simultaneous Chandra/HST Observations of Jupiter Auroral Zones
Elsner, R. F.; Gladstone, G. R.; Waite, J. H. et al

Poster (2003)

Jupiter was observed by the Chandra X-ray Observatory in late February, 2003, for 144 ks, using both the ACIS-S and HRC-I imaging x-ray cameras. Five orbits of HST STIS observations of the planet's ... [more ▼]

Jupiter was observed by the Chandra X-ray Observatory in late February, 2003, for 144 ks, using both the ACIS-S and HRC-I imaging x-ray cameras. Five orbits of HST STIS observations of the planet's northern auroral zone were obtained during the ACIS-S observations. These data are providing a wealth of information about Jupiter's auroral activity, including the first x-ray spectra from the x-ray hot spots inside the auroral ovals. We will also discuss time variability in the auroral x-ray emission and a possible phase relation between the emission from the northern and southern x-ray aurora. [less ▲]

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See detailCassini UVIS time-resolved Jupiter auroral data compared to QP radio bursts
Pryor, W.; Hospodarsky, G.; Stewart, I. et al

Poster (2003)

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Jupiter in a 4-sec integration "high time-resolution mode" on Jan 8, 13-14, and 20-21 in 2001. In this mode Extreme-Ultraviolet and Far ... [more ▼]

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Jupiter in a 4-sec integration "high time-resolution mode" on Jan 8, 13-14, and 20-21 in 2001. In this mode Extreme-Ultraviolet and Far-Ultraviolet spectra were obtained with reduced spectral and spatial resolution in order to study rapid variations in H2 band and H Lyman alpha emission. Previous work has shown that the region inside Jupiter's main auroral ovals contains highly variable spots of emission (auroral flares) that persist for typically 1 or 2 minutes. This duration is similar to that in Jupiter's quasi-periodic (QP) radio bursts. We compare UVIS data to simultaneous Galileo Plasma Wave Subsystem (PWS) and Cassini Radio PWS (RPWS) observations. Jan 8 was an active period for UV variability, that we associate with polar auroral flares. There is a correlation between the radio and UV bursts in this period, suggesting that they are related phenomena. We will also explore coordinated Hubble Space Telescope Imaging Spectrograph time-tagged UV images from Jan 13-14 and Jan 20-21, 2001 to study the spatial properties of the auroral flares. [less ▲]

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See detailTemperature profiles in Jupiter's upper atmosphere
Melin, H.; Stallard, T.; Miller, S. et al

Poster (2003)

Recently, Stallard and coworkers observed an event in Jupiter's auroral polar regions that resulted in a temperature increase of around 125K during the period of approximately seven jovian rotations [1 ... [more ▼]

Recently, Stallard and coworkers observed an event in Jupiter's auroral polar regions that resulted in a temperature increase of around 125K during the period of approximately seven jovian rotations [1]. This "auroral event" involves a great deal of energy being deposited in the upper atmosphere - up to 250mW m[SUP]-2[/SUP]. Stallard et al. made these measurements using H_3^+ emission lines from the fundamental (v=1 rightarrow 0) and hotband (v=2 rightarrow 1) manifolds around 4μm. In this poster, we use the temperature profiles developed by Grodent and coworkers [2] in their one-dimensional model of the jovian aurorae to demonstrate that the lines used by Stallard et al. are formed at different altitudes in the atmosphere: the hotband is formed higher than the fundamental. We show a series of profiles, based on Grodent {et al.}'s original model that can be used to interpret future jovian spectra. [1] T. Stallard et al., 2002. Icarus 156, 498-514. [2] D. Grodent, J. Hunter Waite Jr. and J.-C. G&{acute;e}rard, 2001. J. Geophys. Res. 106, 12933-12952. [less ▲]

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See detailExcitation of the FUV Io tail on Jupiter: Characterization of the electron precipitation
Gérard, Jean-Claude ULg; Gustin, Jacques ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2002), 107(A11),

[1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to ... [more ▼]

[1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to January 2001 have been combined with FUV images to map the FUV color ratio along the STIS slit. Spatially resolved spectra of the aurora carried at similar to12 Angstrom resolution have been used to determine the amount of methane absorption as measured by the FUV color ratio of the Io magnetic footprint and its trailing tail. It is found that the absorption is systematically less than in the main polar aurora, indicating a higher altitude source region. The color ratio of the north tail is shown to slowly decrease downstream from the footprint. The combination of these spectral data with a two-stream model of the interaction of energetic electrons with the Jovian thermosphere indicates that the mean energy of the electrons creating the north FUV emission ranges from similar to55 keV at the Io footprint to similar to40 keV, 20 degrees downstream in the tail. In parallel, the incident electron energy flux drops by a factor similar to6 over the same angular distance. These observations are consistent with the steady state slippage picture where the subcorotating flux tube is accelerated very slowly up to corotation owing to the nonideal coupling. It is argued that small deviations from corotation can supply sufficient energy to fuel the observed auroral emissions. It is suggested that the parallel electric field accelerating electrons out of the flux tube only moderately depends on the time elapsed since the contact with Io, although the mapping between a point in the tail and Io is very uncertain in the presence of magnetic field line slippage. [less ▲]

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See detailLes aurores dans le système solaire
Grodent, Denis ULg

Conference given outside the academic context (2002)

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See detailThe HST Campaign on Jupiter's Aurora during the Cassini Flyby
Clarke, J. T.; Grodent, Denis ULg; Waite, J. H. et al

Conference (2002, July 29)

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See detailCassini UVIS Auroral Observations of Jupiter
Pryor, W.; Stewart, A. I. F.; Esposito, L. et al

Conference (2002, July 29)

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See detailMap of the precipitated electron mean energy in the Jovian aurora
Grodent, Denis ULg; Bouchoms, R.; Gérard, Jean-Claude ULg et al

Conference (2002, June 17)

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See detailThe HST Campaign on Jupiter's Aurora during the Cassini Flyby
Clarke, J. T.; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2002, June 17)

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See detailSpatially resolved far ultraviolet spectroscopy of the jovian aurora
Gustin, Jacques ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Icarus: International Journal of Solar System Studies (2002), 157(1), 91-103

Spatially resolved spectra in four 50-Angstrom FUV spectral windows were obtained across the jovian aurora with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. Nearly ... [more ▼]

Spatially resolved spectra in four 50-Angstrom FUV spectral windows were obtained across the jovian aurora with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. Nearly simultaneous ultraviolet imaging makes it possible to correlate the intensity variations along the STIS slit with those observed in the images and to characterize the global auroral context prevailing at the time of the observations. Spectra at similar to1-Angstrom resolution taken in pairs included an unabsorbed window and a spectral region affected by hydrocarbon absorption. Both sets of spectra correspond to an aurora with a main oval brightness of about 130 kilorayleighs of H-2 emission. The far ultraviolet color ratios I(1550-1620 Angstrom)/I(1230-1300 Angstrom) are 2.3 and 5.9 for the noon and morning sectors of the main oval, respectively. We use an interactive model coupling the energy degradation of incoming energetic electrons, auroral temperature and composition, and synthetic H2 spectra to fit the intensity distribution of the H2 lines. It is found that the model best fitting globally the spectra has a soft energy component in addition to a 10 erg cm(-2) s(-1) flux of 80 keV electrons. It provides an effective H2 temperature of 540 K. The relative intensity of temperature-sensitive H-2 lines indicates differences between the auroral main oval and polar cap emissions. The amount of methane absorption across the polar region is shown to vary in a way consistent with temperature. For the second spectral pair, the polar cap shows a higher attenuation by CH4, indicating a harder precipitation along high-latitude magnetic field lines. (C) 2002 Elsevier Science (USA). [less ▲]

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See detailUltraviolet emissions from the magnetic footprints of Io, Ganymede and Europa on Jupiter
Clarke, J. T.; Ajello, Joseph M.; Ballester, G. et al

in Nature (2002), 415(6875), 997-1000

Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates(1-3). The specific physical mechanisms ... [more ▼]

Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates(1-3). The specific physical mechanisms responsible for generating those emissions are not well understood, but in general the spot seems to arise because of an electromagnetic interaction between Jupiter's magnetic field and the plasma surrounding Io, driving currents of around 1 million amperes down through Jupiter's ionosphere(4-6). The other galilean satellites may also leave footprints, and the presence or absence of such footprints should illuminate the underlying physical mechanism by revealing the strengths of the currents linking the satellites to Jupiter. Here we report persistent, faint, far-ultraviolet emission from the jovian footprints of Ganymede and Europa. We also show that Io's magnetic footprint extends well beyond the immediate vicinity of Io's flux-tube interaction with Jupiter, and much farther than predicted theoretically(4-6); the emission persists for several hours downstream. We infer from these data that Ganymede and Europa have persistent interactions with Jupiter's magnetic field despite their thin atmospheres. [less ▲]

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See detailThe Distorted Shape of Jupiter's North Auroral Oval - A Possible Magnetic Anomaly
Clarke, J. T.; Grodent, Denis ULg; Connerney, J.

Poster (2002)

Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted "kidney bean" shape in the general range of 40-100 deg magnetic longitude, which appears unchanged since 1994 ... [more ▼]

Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted "kidney bean" shape in the general range of 40-100 deg magnetic longitude, which appears unchanged since 1994. More recently, improved accuracy in locating the satellite footprint auroral emissions has provided new information about the geometry of Jupiter's magnetic field in this and other areas. The persistent pattern of the main oval implies a disturbance of the local magnetic field, and the increased latitudinal separation of the locus of satellite footprints from each other and from the main oval implies a locally weaker field strength. It is possible that these phenomena result from a magnetic anomaly in Jupiter's intrinsic magnetic field, as was proposed by A. Dessler in the 1970's. There is presently only limited evidence from the scarcity of auroral footprints observed in this longitude range. Similarly, while it is difficult to observe the conjugate regions in the southern aurora, there does not appear to be any corresponding distortion in the south. We will present the observational evidence that we have accumulated to date, propose future observations to determine the nature of this disturbance, and speculate on its causes and implications. [less ▲]

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