References of "Grodent, Denis"
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See detailMorphology of the Io footprint
Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg

Poster (2007, April 15)

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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See detailA statistical analysis of the location and width of Saturn's aurora, and implications for magnetospheric dynamics
Badman, S. V.; Cowley, S. W. H.; Gérard, Jean-Claude ULg et al

Conference (2006, September)

We present the results of a statistical analysis of the location of commonly-occurring auroral features in Saturn's southern polar ionosphere. Using a magnetospheric model, modified for Saturn from a data ... [more ▼]

We present the results of a statistical analysis of the location of commonly-occurring auroral features in Saturn's southern polar ionosphere. Using a magnetospheric model, modified for Saturn from a data-based terrestrial model (Tsyganenko, 1996), we estimate the region in the equatorial plane of the outer magnetosphere that maps to the observed aurora. We then discuss the possible magnetospheric processes that may cause these auroral emissions. [less ▲]

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See detailIo footprint: Position, Multiplicity, Variability
Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2006, July)

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See detailUltraviolet spectroscopy of giant planets's aurora with HST/STIS, FUSE and Cassini/UVIS
Gustin, Jacques ULg; Gérard, Jean-Claude ULg; Pryor, Wayne et al

Conference (2006, July)

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See detailStudy of the Io footprint short timescale variability
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg

Poster (2006, May)

The electromagnetic interaction between Io and Jupiter leads to single or multiple auroral UV spots in both jovian hemispheres. This study concentrates on short timescale (~1 min) morphological changes of ... [more ▼]

The electromagnetic interaction between Io and Jupiter leads to single or multiple auroral UV spots in both jovian hemispheres. This study concentrates on short timescale (~1 min) morphological changes of the footprints. In order to achieve a sufficient time resolution, we use the time-tag mode of the HST/STIS instrument. This allows us to account for the spots blurring due to the rapid evolution of the jovian magnetic field lines. In addition to the spots motion, our analysis focuses on the spots brightness variations and on the correlation between these variations. The characterization of the parameters herein gives rise to both clues and new questions on the mechanisms that induce the precipitation of energetic electrons. [less ▲]

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See detailMorphology of the ultraviolet Io footprint emission and its control by Io's location
Gérard, Jean-Claude ULg; Saglam, Adem ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2006), 111(A4),

[1] A total of 74 images of the ultraviolet footprint of the Io flux tube (IFT) on Jupiter's upper atmosphere made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope have ... [more ▼]

[1] A total of 74 images of the ultraviolet footprint of the Io flux tube (IFT) on Jupiter's upper atmosphere made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope have been analyzed to characterize their location, morphology, and brightness distribution. The observations cover a wide range of central meridian Jovian longitudes and Io orbital positions and include north and south footprint emissions. Comparing the location of the IFT with that expected from the VIP4 model of the Jovian magnetic field, we find that the lead angle is generally not significantly different from zero in the System III longitude sector 125 degrees - 195 degrees. Instead, the lead angles reach about 8 degrees in the 50 degrees sector, coinciding with a region of possible magnetic anomaly. We observe that the brightness of the main footprint shows intrinsic intensity changes that appear to be controlled by the system III longitude of Io and its position above or below the center of the torus. The size of the primary spot magnetically maps into a region varying from 1 to over 10 Io diameters in Io's orbital plane. Multiple footprints are observed with varying brightness relative to the mean spot. The number of spots is found to increase as Io gets closer to the torus outer edge facing the spots. The separation between the first and second spots is typically 1 degrees-3 degrees of longitude and increases when Io is displaced from the torus center in the direction of the IFT signature. These features confirm that Alfven waves play an important role and generate energization of precipitated electrons. However, the observed variation of the FUV spot structure with Io's position appears inconsistent with models where reflections of Alfven wings occur between the torus boundary and Jupiter's ionosphere. Instead, the multiple spots apparently correspond to electron precipitation generated by Alfven waves reflected inside the plasma torus. [less ▲]

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See detailEuropa's FUV auroral tail on Jupiter
Grodent, Denis ULg; Gérard, Jean-Claude ULg; Gustin, Jacques ULg et al

in Geophysical Research Letters (2006), 33(6),

Ultraviolet images of Jupiter's northern aurora obtained in 2005 confirm the existence of an electromagnetic interaction between Europa and the Jovian ionosphere. The auroral signature shows a two ... [more ▼]

Ultraviolet images of Jupiter's northern aurora obtained in 2005 confirm the existence of an electromagnetic interaction between Europa and the Jovian ionosphere. The auroral signature shows a two-component structure: a quasi-circular Europa spot, followed by a previously undetected faint tail emission trailing in the direction of corotation flow. The characteristic brightness for the auroral spot is similar to 14 +/- 1 kR above background, and approximately 7 +/- 1 kR for the tail. The spot's size is similar to 1100 km, magnetically mapping to an interaction region <= 15 Europa diameters. The auroral tail extends over similar to 5000 km, which maps along a region of at least 70 Europa diameters. The ultraviolet power emitted by both components varies from a fraction to several GW. The present study suggests auroral interaction at Europa similar to that at Io, but scaled-down by an order of magnitude, including a sub-corotating plasma plume in the geometrical wake of Europa. [less ▲]

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See detailEstimated energy balance in the jovian upper atmosphere during an auroral heating event
Melin, Henrik; Miller, Steve; Stallard, Tom et al

in Icarus: International Journal of Solar System Studies (2006), 181(1), 256-265

We present an analysis of a series of observations of the auroral/polar regions of Jupiter, carried out between September 8 and 11, 1998, making use of the high-resolution spectrometer, CSHELL, on the ... [more ▼]

We present an analysis of a series of observations of the auroral/polar regions of Jupiter, carried out between September 8 and 11, 1998, making use of the high-resolution spectrometer, CSHELL, on the NASA InfraRed Telescope Facility (IRTF), Mauna Kea, Hawaii; these observations spanned an "auroral heating event." This analysis combines the measured line intensities and ion velocities with a one-dimensional model vertical profile of the jovian thermosphere/ionosphere. We compute the model line intensities both assuming local thermodynamic equilibrium (LTE) and, relaxing this condition (non-LTE), through detailed balance calculations, in order to compare with the observations. Taking the model parameters derived, we calculate the changes in heating rate required to account for the modelled temperature profiles that are consistent with the measured line intensities. We compute the electron precipitation rates required to give the modelled ion densities that are consistent with the measured line intensities, and derive the corresponding Pedersen conductivities. We compute the changes in heating due to Joule heating and ion drag derived from the measured ion velocities, and modelled conductivities, making use of ion-neutral coupling coefficients derived from a 3-D global circulation model. Finally, we compute the cooling due to the downward conduction of heat and the radiation-to-space from the H-3(+) molecular ion and hydrocarbons. Comparison of the various heating and cooling terms enables us to investigate the balance of energy inputs into the auroral/polar atmosphere. Increases in Joule heating and ion drag are sufficient to explain the observed heating of the atmosphere; increased particle precipitation makes only a minor heating contribution. But local cooling effects-predominantly radiation-to-space-are shown to be too inefficient to allow the atmosphere to relax back to pre-event thermal conditions. Thus we conclude that this event provides observational, i.e. empirical, evidence that heat must be transported away from the auroral/polar regions by thermally or mechanically driven winds. (c) 2005 Elsevier Inc. All rights reserved. [less ▲]

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See detailA statistical analysis of the location and width of Saturn's southern auroras
Badman, S. V.; Cowley, S. W. H.; Gérard, Jean-Claude ULg et al

in Annales Geophysicae [= ANGEO] (2006), 24(12), 3533-3545

A selection of twenty-two Hubble Space Telescope images of Saturn's ultraviolet auroras obtained during 1997-2004 has been analysed to determine the median location and width of the auroral oval, and ... [more ▼]

A selection of twenty-two Hubble Space Telescope images of Saturn's ultraviolet auroras obtained during 1997-2004 has been analysed to determine the median location and width of the auroral oval, and their variability. Limitations of coverage restrict the analysis to the southern hemisphere, and to local times from the post-midnight sector to just past dusk, via dawn and noon. It is found that the overall median location of the poleward and equatorward boundaries of the oval with respect to the southern pole are at similar to 14 degrees and similar to 16 degrees co-latitude, respectively, with a median latitudinal width of similar to 2 degrees. These median values vary only modestly with local time around the oval, though the poleward boundary moves closer to the pole near noon (similar to 12.5 degrees) such that the oval is wider in that sector (median width similar to 3.5 degrees) than it is at both dawn and dusk (similar to 1.5 degrees). It is also shown that the position of the auroral boundaries at Saturn are extremely variable, the poleward boundary being located between 2 degrees and 20 degrees co-latitude, and the equatorward boundary between 6 degrees and 23 degrees, this variability contrasting sharply with the essentially fixed location of the main oval at Jupiter. Comparison with Voyager plasma angular velocity data mapped magnetically from the equatorial magnetosphere into the southern ionosphere indicates that the dayside aurora lie poleward of the main upward-directed field-aligned current region associated with corotation enforcement, which maps to similar to 20 degrees-24 degrees co-latitude, while agreeing reasonably with the position of the open-closed field line boundary based on estimates of the open flux in Saturn's tail, located between similar to 11 degrees and similar to 15 degrees. In this case, the variability in location can be understood in terms of changes in the open flux present in the system, the changes implied by the Saturn data then matching those observed at Earth as fractions of the total planetary flux. We infer that the broad (few degrees) diffuse auroral emissions and sub-corotating auroral patches observed in the dayside sector at Saturn result from precipitation from hot plasma sub-corotating in the outer magnetosphere in a layer a few Saturn radii wide adjacent to the magnetopause, probably having been injected either by Dungey-cycle or Vasyliunas-cycle dynamics on the nightside. [less ▲]

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See detailDynamics of the Io UV footprints: short timescale brightness variations
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg

Conference (2006)

The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple UV spots in both jovian hemispheres. Variations of the multiplicity of the spots and the inter-spots ... [more ▼]

The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple UV spots in both jovian hemispheres. Variations of the multiplicity of the spots and the inter-spots distances have been observed and are linked to the position of Io in its plasma torus. These morphological changes have a timescale of a few hours. We have studied the footprint evolution with a time resolution of a few tens of seconds using the HST/STIS camera in the time-tag mode. This approach resulted in an evaluation of the impact of the rapid evolution of the jovian magnetic field lines when measuring the dimensions of the spots with a longer exposure time. More basically, evidence of strong brightness variations of the main spots (up to 40%) have been observed with a typical growth time of 1 minute. Finally, unexpected simultaneous fluctuations of both primary and secondary spots have also been found in the southern hemisphere. In conclusion, the characterisation of the variations mentioned herein provides clues for a complex and rapidly evolving energetic electrons precipitation mechanism. [less ▲]

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