References of "Grodent, Denis"
     in
Bookmark and Share    
See detailThe HST Auroral Campaign Observations of Jupiter and Saturn
Clarke, John T; Nichols, J.; Gérard, Jean-Claude ULiege et al

in Bulletin of the American Astronomical Society (2008, September 01)

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

While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, auroral emissions on Jupiter and Saturn are thought to be driven primarily by internal processes, with the main energy source being the planetsâ rapid rotation. Limited evidence has 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 one AU and measured near each planet. The data indicate a consistent brightening of both the auroral emissions and Saturn Kilometric Radiation (SKR) 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 situation is less clear, with increases in total auroral power seen near the arrival of solar wind forward shocks, while little increase has been 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 ▲]

Detailed reference viewed: 15 (2 ULiège)
Full Text
See detailObservational evidence of a localized magnetic anomaly near Jupiter’s North Pole
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Gérard, Jean-Claude ULiege et al

Conference (2008, April 18)

We have analyzed more than 1000 HST/ACS images of Jupiter’s ultraviolet auroral emission in the northern hemisphere. A systematic planet center finding algorithm made it possible to infer reliable and ... [more ▼]

We have analyzed more than 1000 HST/ACS images of Jupiter’s ultraviolet auroral emission in the northern hemisphere. A systematic planet center finding algorithm made it possible to infer reliable and consistent jovicentric location of the auroral footprints of Io, Europa and Ganymede. These footprints form reference contours which provide an absolute magnetic mapping from the ionosphere of Jupiter to the equatorial plane, independent of any magnetic field model. So far, the VIP4 magnetic field model is the most accurate in terms of fitting the auroral emissions. However, it cannot reproduce the distorted shape of the satellites UV footpaths in the “kink region” in the northern ionosphere between S3 longitudes 80 ̊-150 ̊. We show that the model is significantly improved by decreasing the VIP4 surface magnetic field in the kink region and by adding a localized dipolar perturbation field beneath the surface. [less ▲]

Detailed reference viewed: 42 (0 ULiège)
Full Text
See detailNew results on the UV Io footprint morphology and brightness
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

Poster (2008, April 18)

The Io UV footprint is an auroral feature on Jupiter caused by the electromagnetic interaction between the satellite Io and the Jovian magnetosphere. The footprint morphology and the spots multiplicity ... [more ▼]

The Io UV footprint is an auroral feature on Jupiter caused by the electromagnetic interaction between the satellite Io and the Jovian magnetosphere. The footprint morphology and the spots multiplicity have been found to vary with the location of Io in the plasma torus. We show recent Hubble Space Telescope (HST) images that reveal a new feature in the footprint: a faint leading spot that appears upstream of the main spot in one hemisphere when Io is close to the opposite border of the torus. A possible interpretation relates the leading spots and one downward secondary spot to electron beams generated by downstream currents in the opposite hemisphere. We also present a 3D model of the Io footprint emissions in the 100 to 170 nm wavelength range. Comparisons between this model and the HST images enable us to study the actual size and shape of the different Io footprint features. It also allows to measure the footprint brightness on the new images with a better estimation of the geometric effects (e.g. limb brightening). The observations presented here provide critical constraints to the Io-plasma torus interaction modeling. [less ▲]

Detailed reference viewed: 11 (0 ULiège)
Full Text
See detailJupiter’s diffuse auroral emissions - Comparison of HST and Galileo data
Radioti, Aikaterini ULiege; Tomás, A. T. M.; Grodent, Denis ULiege et al

Conference (2008, April 18)

Based on an extensive HST FUV image database obtained between 1997 and 2007, we have studied the morphology and brightness of the equatorward diffuse auroral emissions in both Jovian hemispheres. The ... [more ▼]

Based on an extensive HST FUV image database obtained between 1997 and 2007, we have studied the morphology and brightness of the equatorward diffuse auroral emissions in both Jovian hemispheres. The emissions are wider and brighter on the dusk side than on the dawn and they often form multiple discrete arcs parallel to the main oval. What could be the origin of these equatorward diffuse emissions and their local time variations is still unclear. Galileo observations have shown changes in the electron pitch angle distributions between the inner and middle magnetosphere of Jupiter (10 to 17 RJ ) which could be associated with auroral emissions, without the need of field aligned currents. We derive the electron precipitation flux for the first time in a global scale, based on Galileo electron measurements between 10 and 17 RJ . We magnetically map this region in the ionosphere and compare the derived energy flux with the brightness of the diffuse emissions. We discuss the possibility that the energetic particle distribution in the middle magnetosphere could account for the multiple structured equatorward diffuse emissions and their local time variations. [less ▲]

Detailed reference viewed: 6 (1 ULiège)
See detailEvolution of the Io footprint morphology
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

Conference (2008, April)

Detailed reference viewed: 7 (0 ULiège)
See detailJupiter’s diffuse auroral emissions - Comparison of HST and Galileo data,
Radioti, Aikaterini ULiege; Tomàs, A. T. M.; Grodent, Denis ULiege et al

Conference (2008, April)

Detailed reference viewed: 11 (0 ULiège)
Full Text
Peer Reviewed
See detailAuroral polar dawn spots: Signatures of internally driven reconnection processes at Jupiter's magnetotail
Radioti, Aikaterini ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

in Geophysical Research Letters (2008), 35(3), 03104

We report the presence of polar spots located in the dawn auroral region, based on the HST ACS 2007 campaign. We study the location of these features in the equatorial plane as well as their time scales ... [more ▼]

We report the presence of polar spots located in the dawn auroral region, based on the HST ACS 2007 campaign. We study the location of these features in the equatorial plane as well as their time scales and periodicities, based on a comprehensive series of images taken between February 21 and June 11, 2007. It is shown that the majority of polar dawn spots magnetically map to the dawn sector. Additionally, they occur quasi-periodically every 2-3 days, a periodicity observed for the first time in auroral features. Because of their mapped location and their periodic cycle, we interpret the polar dawn spots as signatures of internally driven magnetic reconnection in the Jovian magnetotail. [less ▲]

Detailed reference viewed: 37 (13 ULiège)
Full Text
Peer Reviewed
See detailDiscontinuity in Jupiter's main auroral oval
Radioti, Aikaterini ULiege; Gérard, Jean-Claude ULiege; Grodent, Denis ULiege et al

in Journal of Geophysical Research. Space Physics (2008), 113

On the basis of a series of FUV Hubble Space Telescope images obtained between 1997 and 2007 it is shown that there is a segment of the main auroral oval where the emission drops significantly from a few ... [more ▼]

On the basis of a series of FUV Hubble Space Telescope images obtained between 1997 and 2007 it is shown that there is a segment of the main auroral oval where the emission drops significantly from a few hundreds to a few tens of kiloRayleigh, forming a discontinuity in the oval. It is shown that the discontinuity is present in both hemispheres and confined in magnetic local time. Its equatorial source is located in the prenoon and early noon sector. The main auroral oval is associated with the ionosphere-magnetosphere coupling current system which is related to the breakdown of corotation in the middle magnetosphere. Necessary for the electron precipitation in the ionosphere and the formation of the main auroral oval is the presence of upward field-aligned currents, carried by downward moving electrons. Field-aligned currents inferred by Pioneer, Voyager and Galileo in situ observations in the near equatorial plane showed evidence of reduced or/and downward field-aligned currents in the prenoon and early afternoon sector, the location of the equatorial source of the discontinuity. Additionally, we estimate the precipitation energy flux in the ionosphere, for a typical reduced upward field-aligned current value at that region, which is found to be within the range of the observed brightness of the discontinuity. Field aligned current distributions in the ionosphere based on magnetohydrodynamic simulations of the interaction between the solar wind and the magnetosphere have predicted a region of downward currents implying a discontinuity at the main auroral oval emission, in very good agreement with the HST observations presented in this work. [less ▲]

Detailed reference viewed: 120 (6 ULiège)
Full Text
Peer Reviewed
See detailUV Io footprint leading spot: A key feature for understanding the UV Io footprint multiplicity?
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

in Geophysical Research Letters (2008), 35(5),

The electromagnetic interaction between Io and the Jovian magnetosphere generates a UV auroral footprint in both Jovian hemispheres. Multiple spots were observed in the northern Jovian hemisphere when Io ... [more ▼]

The electromagnetic interaction between Io and the Jovian magnetosphere generates a UV auroral footprint in both Jovian hemispheres. Multiple spots were observed in the northern Jovian hemisphere when Io was in the northern part of the plasma torus and vice-versa for the South. Based on recent Hubble Space Telescope (HST) measurements, we report here the discovery of a UV leading spot, i.e., a faint emission located ahead of the main spot. The leading spot emerges at System III longitudes between 0 degrees and 100 degrees in the northern hemisphere and between 130 degrees and 300 degrees in the southern hemisphere, i. e., in one hemisphere when multiple spots are observed in the other hemisphere. We propose as one potential mechanism that electron beams observed near Io are related to the generation of the leading spot and the secondary spot in the opposite hemisphere. [less ▲]

Detailed reference viewed: 74 (12 ULiège)
Full Text
Peer Reviewed
See detailAuroral current systems in Saturn's magnetosphere: comparison of theoretical models with Cassini and HST observations
Cowley, S. W. H.; Arridge, C. S.; Bunce, E. J. et al

in Annales Geophysicae (2008), 26(9), 2613-2630

The first simultaneous observations of fields and plasmas in Saturn's high-latitude magnetosphere and UV images of the conjugate auroral oval were obtained by the Cassini spacecraft and the Hubble Space ... [more ▼]

The first simultaneous observations of fields and plasmas in Saturn's high-latitude magnetosphere and UV images of the conjugate auroral oval were obtained by the Cassini spacecraft and the Hubble Space Telescope (HST) in January 2007. These data have shown that the southern auroral oval near noon maps to the dayside cusp boundary between open and closed field lines, associated with a major layer of upward-directed field-aligned current (Bunce et al., 2008). The results thus support earlier theoretical discussion and quantitative modelling of magnetosphere-ionosphere coupling at Saturn (Cowley et al., 2004), that suggests the oval is produced by electron acceleration in the field-aligned current layer required by rotational flow shear between strongly sub-corotating flow on open field lines and near-corotating flow on closed field lines. Here we quantitatively compare these modelling results (the 'CBO' model) with the Cassini-HST data set. The comparison shows good qualitative agreement between model and data, the principal difference being that the model currents are too small by factors of about five, as determined from the magnetic perturbations observed by Cassini. This is suggested to be principally indicative of a more highly conducting summer southern ionosphere than was assumed in the CBO model. A revised model is therefore proposed in which the height-integrated ionospheric Pedersen conductivity is increased by a factor of four from 1 to 4 mho, together with more minor adjustments to the co-latitude of the boundary, the flow shear across it, the width of the current layer, and the properties of the source electrons. It is shown that the revised model agrees well with the combined Cassini-HST data, requiring downward acceleration of outer magnetosphere electrons through a similar to 10 kV potential in the current layer at the open-closed field line boundary to produce an auroral oval of similar to 1 degrees width with UV emission intensities of a few tens of kR. [less ▲]

Detailed reference viewed: 61 (22 ULiège)
Full Text
Peer Reviewed
See detailAuroral evidence of a localized magnetic anomaly in Jupiter's northern hemisphere
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Gérard, Jean-Claude ULiege et al

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

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede ... [more ▼]

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede form individual footpaths, which are fitted with three reference contours. The satellite footprints provide a convenient mapping between the northern Jovian ionosphere and the equatorial plane in the middle magnetosphere, independent of any magnetic field model. The VIP4 magnetic field model is in relatively good agreement with the observed footprint of Io. However, in the auroral kink sector, between the 80 degrees and 150 degrees System III meridians, the model significantly departs from the observation. One possible way to improve the agreement between the VIP4 model and the observed footprints is to include a magnetic anomaly. We suggest that this anomaly is characterized by a weakening of the surface magnetic field in the kink sector and by an added localized tilted dipole field. This dipole rotates with the planet at a depth of 0.245 R-J below the surface, and its magnitude is set to similar to 1% of Jupiter's dipole moment. The anomaly has a very limited influence on the magnetic field intensity in the equatorial plane between the orbits of Io and Ganymede. However, it is sufficient to bend the field lines near the high-latitude atmosphere and to reproduce the observed satellite ultraviolet footpaths. JUNO's in situ measurements will determine the structure of Jupiter's magnetic field in detail to expand on these results. [less ▲]

Detailed reference viewed: 120 (34 ULiège)
Full Text
Peer Reviewed
See detailSpectral morphology of the X-ray emission from Jupiter's aurorae
Branduardi-Raymont, G.; Elsner, Ronald F.; Galand, M. et al

in Journal of Geophysical Research (2008), 113(A2),

Simultaneous Chandra X-ray and Hubble Space Telescope FUV observations of Jupiter's aurorae carried out in February 2003 have been re-examined to investigate the spatial morphology of the X-ray events in ... [more ▼]

Simultaneous Chandra X-ray and Hubble Space Telescope FUV observations of Jupiter's aurorae carried out in February 2003 have been re-examined to investigate the spatial morphology of the X-ray events in different energy bands. The data clearly show that in the Northern auroral region (in the main auroral oval and the polar cap) events with energy > 2 keV are located at the periphery of those with energy < 2 keV and coincide with FUV bright features. In addition, X-ray spectra extracted from the areas where the two event distributions are concentrated possess different shapes. We associate the > 2 keV events (similar to 45 MW emitted power) with the electron bremsstrahlung component recently revealed by XMM-Newton in the spectra of Jupiter's aurorae, and the < 2 keV emission (similar to 230 MW) with the product of ion charge exchange, now established as the likely mechanism responsible for the soft X-ray Jovian aurora. We suggest that the same population of energetic electrons may be responsible for both, the X-ray bremsstrahlung and the FUV emission of Jupiter's aurorae. Comparison of the > 2 keV X-ray and FUV (340 GW) powers measured during the observations shows that they are broadly consistent with the predicted emissions from a population of energetic electrons precipitating in the planet's atmosphere, thus supporting our interpretation. [less ▲]

Detailed reference viewed: 34 (8 ULiège)
Full Text
Peer Reviewed
See detailJupiter's changing auroral location
Grodent, Denis ULiege; Gérard, Jean-Claude ULiege; Radioti, Aikaterini ULiege et al

in Journal of Geophysical Research (2008), 113(A1),

[1] We examine the case of significant latitudinal shifts of the Jovian northern auroral emissions appearing in a data set spanning nine years of observations with the Hubble Space Telescope in the far ... [more ▼]

[1] We examine the case of significant latitudinal shifts of the Jovian northern auroral emissions appearing in a data set spanning nine years of observations with the Hubble Space Telescope in the far ultraviolet. The extended data set makes it possible to compare the location of the main auroral emission with similar viewing geometries and satellite positions. The main auroral emission is assumed to originate from beyond the orbit of Ganymede (15 Jovian radii). At these distances, near corotation enforcement and transfer of momentum from Jupiter to the magnetospheric plasma is ensured by means of field aligned currents. The field aligned currents away from Jupiter are carried by downward energetic electrons loosing their energy to the polar atmosphere and giving rise to the main auroral emission. Analysis of the polar projected images shows that the latitudinal location of the main emission has changed by up to 3 degrees over long periods of time. It also shows that the footprint of Ganymede follows a similar trend. We have used the VIP4 magnetic field model to map the emission down to the equatorial plane. This mapping suggests that internal variations of the current sheet parameters might be used as an alternative or complementary explanation to the changing solar wind conditions at Jupiter to explain the observed shift of auroral latitudes. [less ▲]

Detailed reference viewed: 49 (18 ULiège)
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 ULiège)
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: 46 (11 ULiège)
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: 41 (1 ULiège)