References of "Grodent, Denis"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailOrigin of Saturn's aurora: Simultaneous observations by Cassini and the Hubble Space Telescope
Bunce, E. J.; Arridge, C. S.; Clarke, J. T. et al

in Journal of Geophysical Research (2008), 113(A9),

Outer planet auroras have been imaged for more than a decade, yet understanding their physical origin requires simultaneous remote and in situ observations. The first such measurements at Saturn were ... [more ▼]

Outer planet auroras have been imaged for more than a decade, yet understanding their physical origin requires simultaneous remote and in situ observations. The first such measurements at Saturn were obtained in January 2007, when the Hubble Space Telescope imaged the ultraviolet aurora, while the Cassini spacecraft crossed field lines connected to the auroral oval in the high-latitude magnetosphere near noon. The Cassini data indicate that the noon aurora lies in the boundary between open- and closed-field lines, where a layer of upward-directed field-aligned current flows whose density requires downward acceleration of magnetospheric electrons sufficient to produce the aurora. These observations indicate that the quasi-continuous main oval is produced by the magnetosphere-solar wind interaction through the shear in rotational flow across the open-closed-field line boundary. [less ▲]

Detailed reference viewed: 63 (33 ULg)
Full Text
Peer Reviewed
See detailOscillation of Saturn's southern auroral oval
Nichols, J. D.; Clarke, J. T.; Cowley, S. W. H. et al

in Journal of Geophysical Research (2008), 113(A11),

Near-planetary-period oscillations in the Cassini plasma and magnetic field data have been observed throughout Saturn's magnetosphere despite the fact that Saturn's internal magnetic field is apparently ... [more ▼]

Near-planetary-period oscillations in the Cassini plasma and magnetic field data have been observed throughout Saturn's magnetosphere despite the fact that Saturn's internal magnetic field is apparently highly axisymmetric. In addition, the period of the Saturn kilometric radiation has been shown to vary over time. In this paper we present results from the recent Hubble Space Telescope observations of Saturn's southern ultraviolet auroral emission. We show that the center of the auroral oval oscillates with period 10.76 h +/- 0.15 h for both January 2007 and February 2008, i.e., close to the periods determined for oscillations in other magnetospheric phenomena. The motion of the oval center is described for 2007 by an ellipse with semimajor axis similar to 1.4 degrees +/- 0.3 degrees oriented toward similar to 09-21 h LT, eccentricity similar to 0.93, and center offset from the spin axis by similar to 1.8 degrees toward similar to 04 h LT. For 2008 the oscillation is consistent with an ellipse with semimajor axis similar to 2.2 degrees +/- 0.3 degrees oriented toward similar to 09-21 h LT, eccentricity similar to 0.99, and a center offset from the spin axis by similar to 2.2 degrees toward similar to 03 h LT. The motion of the auroral oval is thus highly elliptical in both cases, and the major oscillation axis is oriented toward prenoon/premidnight. This result places an independent constraint on the magnitude of the planet's dipole tilt and may also indicate the presence of an external current system that imposes an asymmetry in the ionospheric field modulated close to the planetary period. [less ▲]

Detailed reference viewed: 44 (11 ULg)
See detailAuroral Movies and Spectroscopy from Cassini UVIS
Pryor, W. R.; West, R.; Stewart, I. et al

Conference (2007, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting us to create images, spectra, and at times movies. We will present an auroral movie from 2007-145 that has been processed to remove flat-fielding artifacts and deconvolved to remove scattering along the slit. The movie shows near co- rotation of N polar auroral features with the planet's rotation. An auroral oval is present. The oval appears doubled on the midnight side. Other images from this year show emissions inside the auroral oval. We will discuss these images and their spectra. Additional images and movies are planned in coming months. [less ▲]

Detailed reference viewed: 38 (1 ULg)
See detailMeasured Correlations of Auroral Emissions from Jupiter and Saturn With Solar Wind Variations
Clarke, J. T.; Nichols, J.; Gérard, Jean-Claude ULg et al

Conference (2007, December 01)

An extended set of Hubble Space Telescope (HST) observations of the UV auroral emissions from Jupiter and Saturn has been carried out in three campaigns over Jan.-June 2007. This is by far the most ... [more ▼]

An extended set of Hubble Space Telescope (HST) observations of the UV auroral emissions from Jupiter and Saturn has been carried out in three campaigns over Jan.-June 2007. This is by far the most extensive series of remote high resolution imaging of planetary aurora to date, and provides new physical insight into the cause and effect relationships governing the controlling processes for the giant planet auroral emissions. Simultaneous in situ measurements of local solar wind and magnetospheric plasma conditions have been made during two of these campaigns by Cassini at Saturn in Jan. 2007 and by the New Horizons mission approaching Jupiter in Feb. 2007. The UV auroral emission brightness and distributions have also been compared with estimates of the solar wind conditions near each planet extrapolated from near-Earth measurements, which can be verified by comparison with Cassini and New Horizons in situ data. It has been found that there is a good correlation at both planets between total auroral power and solar wind dynamic pressure, at least for the major solar wind disturbances arriving at each planet. At the same time, the nature of the auroral brightenings differs between Jupiter and Saturn, and the source regions of auroral activity are quite different in the two magnetospheres. In this presentation, the HST and solar wind data and the nature of the correlations will be presented. The physical significance of the correlations will be discussed, based on the much denser set of measurements now available. [less ▲]

Detailed reference viewed: 31 (1 ULg)
Full Text
See detailJupiter’s polar auroral emissions-signatures of magnetic reconnection
Radioti, Aikaterini ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2007, August 23)

The polar auroral emissions at Jupiter can be divided into three regions fixed in mag- netic local time: the dawnside dark region, the poleward swirl region and the duskside active region in which flares ... [more ▼]

The polar auroral emissions at Jupiter can be divided into three regions fixed in mag- netic local time: the dawnside dark region, the poleward swirl region and the duskside active region in which flares and arc-like features are observed. Previous studies re- lated the polar emissions to the solar wind driven Dungey cycle and Vasyliunas flow cycle. Based on HST STIS and ACS images we study extensively the time variations of the morphology and brightness of various polar auroral features as well as their duration and reoccurrence. We magnetically map their location in the equatorial plane and we compare their spatial size and time scales with the reconnection events taking place in the Jovian magnetotail. We discuss the possibility that some polar auroral features are signatures of magnetic reconnection. [less ▲]

Detailed reference viewed: 8 (1 ULg)
See detailJupiter's changing auroral location
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2007, June 25)

Detailed reference viewed: 6 (1 ULg)
See detailCassini UVIS Observations of Saturn's Auroras
Pryor, W. J.; Ajello, J. M.; Gustin, Jacques ULg et al

Conference (2007, June 25)

Detailed reference viewed: 15 (3 ULg)
See detailThe auroral footprint signatures of satellites on Jupiter
Gérard; Bonfond, Bertrand ULg; Grodent, Denis ULg

Conference (2007, June 25)

Detailed reference viewed: 7 (0 ULg)
See detailThe morphology of the X-ray emission above 2 keV from Jupiter's aurorae
Elsner, R. F.; Branduardi-Raymont, G.; Galand, M. et al

Conference (2007, June 25)

Detailed reference viewed: 11 (0 ULg)
See detailDiscontinuity in Jupiter's main auroral oval
Radioti, Aikaterini ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2007, April 15)

Detailed reference viewed: 5 (0 ULg)
See detailJupiter’s main auroral oval: what main oval?
Grodent, Denis ULg; Gérard, Jean-Claude ULg; Radioti, Aikaterini ULg et al

Poster (2007, April 15)

Detailed reference viewed: 7 (2 ULg)
See detailMorphology of the Io footprint
Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg

Poster (2007, April 15)

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailResponse of Jupiter's UV auroras to interplanetary conditions as observed by the Hubble Space Telescope during the Cassini flyby campaign
Nichols, J. D.; Bunce, E. J.; Clarke, John T. et al

in Journal of Geophysical Research. Space Physics (2007), 112(A2),

We provide a first detailed discussion of the relation between the set of Jovian UV auroral images observed by the Hubble Space Telescope ( HST) in December 2000 to January 2001 and simultaneous ... [more ▼]

We provide a first detailed discussion of the relation between the set of Jovian UV auroral images observed by the Hubble Space Telescope ( HST) in December 2000 to January 2001 and simultaneous interplanetary data obtained by Cassini during its Jupiter flyby. Examination of the interplanetary data surrounding all seven HST observation intervals shows that by chance six of them correspond to solar wind rarefaction regions, which follow compressions by periods of similar to 2 to similar to 6 days. Only one imaging interval, on 13 January 2001, corresponds to a compression region of generally elevated, but highly variable, solar wind dynamic pressure and interplanetary field strength. We have thus first examined the images corresponding to rarefaction regions in order to establish the range of behaviors that occur under these known conditions, which then act as a benchmark against which the compression region images can be compared. The rarefaction region images show relatively consistent properties of the main oval auroras, though differing in detail from interval to interval. The polar auroras show more variability, with the patchy ("swirl") auroras in the central region sometimes forming a diffuse ring structure and at other times being more uniformly distributed, while the "active region" auroras at dusk vary markedly from weak emissions to bright arc-like forms, the latter possibly being associated with intervals within similar to 2 - 3 days of a previous solar wind compression. The two images obtained in the compression region on 13 January 2001 then show remarkably different properties in all the auroral components. The main oval is found to be brighter over its whole length by factors of two to three compared with the rarefaction region images, while its position remains essentially unchanged, close to the usual reference oval. However, bright contiguous "active region" auroras in the postnoon and dusk sector then widen the overall auroral distribution in that sector by up to similar to 5 degrees in the poleward direction. The region of patchy polar auroras is also found to expand to cover essentially the whole of the remaining area of the polar cap, with a much-narrowed darker zone just poleward of the main oval in the dawn and prenoon sector. We discuss whether these enhanced emissions are characteristic of the few-day compression region as a whole or of more localized conditions occurring within the compression region and conclude that the latter is more likely. Examination of the relevant interplanetary data then shows that the brightened images are associated with an interval of significant magnetospheric dynamics, involving a modest compression of the magnetosphere followed by an extended major expansion. [less ▲]

Detailed reference viewed: 50 (5 ULg)
Full Text
Peer Reviewed
See detailUltraviolet Io footprint short timescale dynamics
Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

in Geophysical Research Letters (2007), 34(6),

The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple ultraviolet spots near the feet of the Io flux tube. Variations of spot numbers and brightness and of ... [more ▼]

The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple ultraviolet spots near the feet of the Io flux tube. Variations of spot numbers and brightness and of interspot distances have been observed to be linked to Io's position in its plasma torus. We have studied the evolution of the Io UV footprints with a time resolution of a few tens of seconds using the Space Telescope Imaging Spectrograph (STIS) in time-tag mode. We present evidence of systematic strong brightness variations of the main spots ( up to 50%) with a typical growth time of 1 minute. Additionally, unanticipated simultaneous fluctuations of both primary and secondary spots have also been found in the southern hemisphere. Our findings suggest that the footprint brightness is not only actively controlled by the plasma directly interacting with Io but also by the poorly constrained electron acceleration region between Io and Jupiter. [less ▲]

Detailed reference viewed: 92 (20 ULg)
Full Text
See detailA new interpretation of the Io UV footprint morphology
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2007)

The electromagnetic interaction between Io and the jovian magnetic field leads to an auroral UV footprint consisting of single or multiple UV spots in both jovian hemi- spheres. According to current ... [more ▼]

The electromagnetic interaction between Io and the jovian magnetic field leads to an auroral UV footprint consisting of single or multiple UV spots in both jovian hemi- spheres. According to current theories, the perturbation induced by the motion of Io in the plasma torus propagates along the field lines in the form of Alfvén waves and finally causes electron precipitation in the jovian ionosphere. The occurrence and mul- tiplicity of the secondary spots appear to be related to the position of Io in the plasma torus and have been attributed to partial reflections of the Alfvén waves on the torus boundaries. Nevertheless, the discrepancies between the predicted inter-spot distances and the measurements were found difficult to explain. Additionally, some crucial con- figurations of Io in the torus had never been observed. Our recent HST/ACS observations of the footprint in so far unexplored Io-plasma torus configurations lead to the finding of a new feature in the footprint: a faint spot upstream of the main spot. The observations of this precursor emission, together with the inconsistencies related to the inter-spot distances, suggest a new interpretation of the footprint morphology. We propose that the precursor and the first secondary spot stem from the same mechanism and we interpret them as the counterparts of the main spot occurring in the opposite hemisphere. [less ▲]

Detailed reference viewed: 10 (1 ULg)
See detailSaturn's Auroras and Polar Atmosphere from Cassini UVIS
Pryor, W. R.; West, R.; Larsen, K. et al

Conference (2006, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn, with sufficient spatial resolution to image Saturn's auroral oval when Cassini leaves Saturn's equatorial plane. We will present new images and time-series data from summer 2006. Detailed spectral models of molecular hydrogen auroral emissions that include hydrocarbon absorption and hydrogen self- absorption have now been compared to UVIS data. We are analyzing a UV spectral feature detected in an auroral oval image from 2005. The feature is an absorption feature concentrated inside the oval, at wavelengths dominated by reflected sunlight and acetylene absorption. The absorption feature appears as a broad absorption "scoop". One plausible molecule that has a similar absorption feature is benzene, which has a cross-section some 500 times larger than acetylene in this spectral region. Thus UVIS is sensitive to small quantities of benzene. Enhanced polar benzene has been previously observed at Jupiter and can be generated in coupled photochemical/auroral models. We will explore the uniqueness of this interpretation, and compare the inferred benzene abundances to results from complementary Cassini CIRS infrared observations. Additional out of the equatorial plane UVIS Saturn data planned for the coming months will improve the signal- to-noise ratio and spatial resolution on the auroral ovals and their interior. Coordinated observations with Cassini VIMS and Hubble Space Telescope are being scheduled for 2007. [less ▲]

Detailed reference viewed: 37 (2 ULg)
See detailComprehensive auroral imaging of Saturn during the International Heliophysical Year
Nichols, J. D.; Clarke, J. T.; Duval, J. et al

Conference (2006, December 01)

As part of the International Heliophysical Year in 2007, a large-scale campaign is planned to observe the UV auroras of Jupiter and Saturn with the Hubble Space Telescope (HST). In this talk we will ... [more ▼]

As part of the International Heliophysical Year in 2007, a large-scale campaign is planned to observe the UV auroras of Jupiter and Saturn with the Hubble Space Telescope (HST). In this talk we will provide an overview of the Saturn campaign. Previous HST observations of Saturn's auroras have greatly extended our knowledge of the processes that occur in the planet's magnetosphere. In particular, Saturn's main oval auroras vary much more than Jupiter's in terms of latitudinal position and extent, and have been shown to be correlated with the conditions in the solar wind. However, these campaigns have generally been limited by their short-term nature, and in order to establish exactly how the auroras depend on the solar wind we must make observations continually over at least one complete solar rotation. This is the goal of the 2007 campaign, in which Saturn will be observed for a period of 30 days in January and February. The timing is fortuitous since not only will the planet be in opposition, allowing near-Earth measurements of the interplanetary medium to be extrapolated to Saturn's orbit, the Cassini spacecraft will be in a position to obtain in-situ plasma and magnetic field measurements from the magnetosphere and solar wind. Cassini will also make observations of Saturn's UV and SKR emissions throughout the campaign, and the planet will be observed by ground-based IR and radio telescopes. Here we provide a brief review of our current understanding of Saturn's auroras, along with an overview of the coordinated observations planned at Saturn and the key science goals we aim to address. [less ▲]

Detailed reference viewed: 24 (1 ULg)
Full Text
Peer Reviewed
See detailSaturn's auroral morphology and activity during quiet magnetospheric conditions
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Cowley, S. W. H. et al

in Journal of Geophysical Research. Space Physics (2006), 111

We report the results of a coordinated Hubble Space Telescope-Cassini campaign that took place between 26 October and 2 November 2005. During this period, Saturn's magnetosphere was in an expanded state ... [more ▼]

We report the results of a coordinated Hubble Space Telescope-Cassini campaign that took place between 26 October and 2 November 2005. During this period, Saturn's magnetosphere was in an expanded state and the solar wind was quiet, as indicated by the location of the magnetopause, in situ particle measurements, weak auroral SKR emission, and the generally low brightness of the aurora. We describe the morphology and dynamics of the aurora during this period in parallel with concurrent Cassini measurements. We show that the aurora exhibits considerable longitudinal structure and time variations over intervals of a few hours, in spite of the absence of observable external triggers and generally low intensity. In particular, enhancements of the dawn-morning oval are seen while no apparent indication of solar wind activity is observed. These features rotate at a speed corresponding to about 65% of the planet's angular velocity. We also describe energetic neutral atom measurements indicating that an ENA acceleration event occurred in the magnetotail on 26 October without any measured signature of solar wind activation. These observations suggest an intrinsically dynamical magnetosphere where injection of hot plasma occasionally takes place in the night or dawn sector during quiet magnetospheric conditions, possibly connected with either the Dungey or the Vasyliunas convection cycle. [less ▲]

Detailed reference viewed: 32 (5 ULg)
See detailThe HST UV Auroral Imaging Campaign of Jupiter and Saturn during the International Heliophysical Year
Clarke, J. T.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2006, December 01)

An extended campaign of observations of the UV auroral emissions from Jupiter and Saturn is scheduled for three periods beginning in Jan. 2007 and ending in late June 2008. This will be by far the most ... [more ▼]

An extended campaign of observations of the UV auroral emissions from Jupiter and Saturn is scheduled for three periods beginning in Jan. 2007 and ending in late June 2008. This will be by far the most extensive series of remote high resolution imaging of planetary aurora to date, and should provide new physical insight into the cause and effect relationships governing the controlling processes for the giant planet auroral emissions. These observations will overlap with in situ measurements of local solar wind and magnetospheric plasma conditions by Cassini at Saturn in Jan. 2007 and by the New Horizons mission approaching Jupiter in Feb. 2007. The UV auroral emission brightness and distributions will also be compared with extrapolated estimates of the solar wind conditions near each planet from periods just before planetary opposition in Jan. 2007 (Saturn) and June 2007 (Jupiter). The HST observations will also be coordinated with ground-based observations of near-IR auroral and nonthermal radio emissions. This paper will give an overview of the program, including the schedule of HST observations and the schedule of known coordinated observations. While a preliminary schedule has been submitted for the HST observations, this schedule will be finalized only when the HST orbit is sufficiently well known for the periods of observation for detailed pointing to be specified. By the time of Fall AGU, it should be possible to show the detailed schedule and pointing for the Jan-Feb 2007 observations. The paper will include a presentation of the plans for the rapid reduction and distribution of the HST auroral images to the community. [less ▲]

Detailed reference viewed: 40 (1 ULg)
Full Text
Peer Reviewed
See detailCharacteristics of Jovian morning bright FUV aurora from Hubble Space Telescope/Space Telescope Imaging Spectrograph imaging and spectral observations
Gustin, Jacques ULg; Cowley, S. W. H.; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2006), 111(A9),

Observation of an exceptionally bright (peaking at similar to 1.8 MR) Jovian auroral morning arc was obtained with the Space Telescope Imaging Spectrograph (STIS) on 21 September 1999, both in the imaging ... [more ▼]

Observation of an exceptionally bright (peaking at similar to 1.8 MR) Jovian auroral morning arc was obtained with the Space Telescope Imaging Spectrograph (STIS) on 21 September 1999, both in the imaging and spectral modes. The images of the HST orbit are used to describe the variation of the position of the bright arc, while the time-tagged spectra are examined to derive the properties of the precipitating auroral electrons, such as their mean energy and the electron current density at the top of the atmosphere. The first and the last images of the HST orbit, separated by 37 min, show that the bright morning emission is situated on the reference oval, with a "leading" edge fixed in lambda(III) longitudes (i.e., rotating with the planet), and a "trailing" edge that extends into the nightside. The auroral arc is divided in two branches, as was also observed in some previous analyses. An isolated bright spot is also observed at lambda(III) similar to 184 degrees. Its brightness reaches 500 kR and it also approximately corotates with Jupiter. Four regions of the auroral morning arc captured by the STIS aperture were extracted from the spectral observation. The four associated low-resolution spectra (similar to 4.8 degrees) show very different characteristics. In particular, two spectra reveal unusually high color ratios (18.5 and 45.5), with corresponding mean electron energies of similar to 280 and similar to 460 keV, respectively. The current densities associated with three of the spectra lie in the range 0.09-0.2 mu A m(-2), consistent with previous estimates, while the fourth spectrum is characterized by a mean current density of 0.54 mu A m(-2), outside the range similar to 0.04-0.4 mu A m(-2) obtained in a previous study of G140L spectra of the Jovian main oval. Assuming that main oval aurorae are caused by field-aligned electric fields, the relationship between the energy flux and the current density derived from the spectra has been compared to the Knight's theory of field-aligned currents. Because of the very high acceleration potential derived from two of the extracted spectra, a relativistic treatment of the Knight theory was used. Assuming an electron temperature T-e = 2.5 keV, it is seen that the two regions corresponding to earlier local times (higher lambda(III) longitudes) reveal an electron source density lower than the values observed in the equatorial plane during the Voyager flybys. On the other hand, the equatorward region (lowest latitude) exhibits an electron source density in the upper range of usual values. Analysis of time-tag spectra reveals that the variations of the energy flux and the color ratios are large but continuous and generally covary. [less ▲]

Detailed reference viewed: 46 (5 ULg)