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See detailAuroral Processes at Earth, Jupiter and Saturn.
Grodent, Denis ULg

Conference (2004, May 17)

We review the main characteristics of the auroral ultraviolet emissions at Earth, Jupiter and Saturn. Based on auroral morphology considerations, we discuss and compare the different solar wind ... [more ▼]

We review the main characteristics of the auroral ultraviolet emissions at Earth, Jupiter and Saturn. Based on auroral morphology considerations, we discuss and compare the different solar wind - magnetosphere - ionosphere coupling processes giving rise to these emissions. Earth's magnetosphere is usually described as 'open', meaning that its field reconnects with the interplanetary magnetic field (IMF) frozen in the solar wind. This reconnection process allows solar-wind plasma and energy to be transferred to the magnetosphere and to provide the main driving force for the auroral emissions. Different cases of solar-wind plasma conditions have been recognized to give rise to different types of auroral features. Jupiter is opposed to Earth, with a 'closed' magnetosphere. Its larger distance to the Sun and its enormous magnetic field make it difficult for the reconnection process with the IMF to occur efficiently. Io's volcanism is considered to be the prime (internal) plasma source for the magnetosphere, and corotation enforcement of this outward moving plasma is the likely process generating field aligned currents, responsible for the main auroral emissions. Saturn's aurora has not been as extensively studied as Earth's and Jupiter's. Owing to fainter magnetic field and internal plasma source than Jupiter, it has been expected to be intermediate between the cases of Earth and Jupiter. Recent detailed analysis of the Terrestrial, Jovian and Saturnian auroral morphology and dynamics suggests that the simple open/closed/open-closed magnetosphere picture is somewhat oversimplified. They show a much more complex situation with, for example, auroral activity without solar-wind reconnection at Earth, Earth-like reconnection signatures at Jupiter, or extreme auroral variability at Saturn. [less ▲]

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See detailAuroral processes at the outer planets
Gérard, Jean-Claude ULg

Conference (2010, January 04)

The mean electron energy may be significantly different in different auroral zones. The Io tail CR is remarkably low in comparison with the high-latitude aurora and independent of its brightness (<E> ~ 50 ... [more ▼]

The mean electron energy may be significantly different in different auroral zones. The Io tail CR is remarkably low in comparison with the high-latitude aurora and independent of its brightness (<E> ~ 50 keV or less). This is consistent with a model where the tail corresponds to an upward field aligned current closing the magnetospheric circuit in Jupiter’s ionosphere. The CR in the main oval is associated with electron energies from ~50 to several 100 keV. It is statistically positively correlated with the intensity. Brightness increase in the main oval is accompanied by hardening of the electron energy spectrum. This result is consistent with acceleration by potential drops accompanying upward field-aligned currents which carry a nearly constant particle number flux. The electron mean energy is also variable in the polar spots but it is not correlated with the main oval brightness nor its own intensity, suggesting different, uncorrelated mechanisms. Polar brightenings (duration ~ 50-100 sec, rise time ~30 sec) have been observed. They are not necessarily associated with an increase of the mean electron energy. The mean electron energy can even decrease during the intensification. No correlation is observed between changes in main oval and high latitude (polar cap) features. [less ▲]

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See detailAuroral Signature of the Interaction of Comet Shoemaker-Levy 9 with the Jovian Magnetosphere
Prangé; Emerich, C.; Rego, D. et al

in Bulletin of the American Astronomical Society (1994, June 01)

Not Available

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See detailAuroral signatures of flow bursts released during magnetotail reconnection at Jupiter
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2010), 115

Recent studies based on Hubble Space Telescope (HST) data reported the presence of transient polar dawn spots in the Jovian auroral region and interpreted them as signatures of internally driven magnetic ... [more ▼]

Recent studies based on Hubble Space Telescope (HST) data reported the presence of transient polar dawn spots in the Jovian auroral region and interpreted them as signatures of internally driven magnetic reconnection in the Jovian magnetotail. Even though an association of the polar dawn spots with the reconnection process has been suggested, it has not been yet investigated which part of the process and what mechanism powers these auroral emissions. In the present study, we examine the scenario that the auroral spots are triggered by the inward moving flow bursts released during magnetic reconnection at Jupiter. We base our analysis on a model adapted from the terrestrial case, according to which moving plasma flow burst is coupled with the ionosphere by field-aligned currents, giving rise to auroral emissions. We estimate the upward field-aligned current at the flank of the flow bursts, using in-situ magnetic field measurements and we derive the auroral emitted power. We statistically study the observed emitted power of the polar dawn spots, based on HST data from 1998 to 2007, and we compare it with the emitted power derived according to the proposed scenario. Apart from the emitted power, other properties of the polar dawn spots such as their location, periodicity, duty cycle and multiplicity suggest that they are associated with the inward moving flow bursts released during magnetic reconnection in Jupiter's tail. [less ▲]

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See detailAuroral signatures of injections in the magnetosphere of Saturn
Radioti, Aikaterini ULg; Roussos, E.; Grodent, Denis ULg et al

Poster (2011, July 11)

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See detailAuroral signatures of multiple magnetopause reconnection at Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2013)

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See detailAuroral signatures of reconnection at Saturn and comparison with Earth
Radioti, Aikaterini ULg

Conference (2014, July)

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See detailAn auroral source of hot oxygen in the geocorona
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Geophysical Research Letters (2005), 32

The high-energy proton-hydrogen (H[SUP]+[/SUP]/H) beam associated with proton auroral precipitation transfers momentum in elastic and inelastic collisions with ambient thermal atomic oxygen in the high ... [more ▼]

The high-energy proton-hydrogen (H[SUP]+[/SUP]/H) beam associated with proton auroral precipitation transfers momentum in elastic and inelastic collisions with ambient thermal atomic oxygen in the high latitude thermosphere. This process provides a localized novel source of hot oxygen atoms in addition to exothermic photochemistry, charge exchange and momentum transfer from O[SUP]+[/SUP] ion precipitation and charge exchange with accelerated ionospheric O[SUP]+[/SUP] ions. We suggest that this source contributes to the population of the hot oxygen geocorona and to the flux of escaping oxygen atoms. For an incident proton energy flux of 1 mW m[SUP]-2[/SUP] and a mean energy E[SUB]mean[/SUB] ~ 5 keV, we calculate a density of hot oxygen atoms with energy above 1 eV of 2.0 × 10[SUP]3[/SUP] cm[SUP]-3[/SUP] and a mean kinetic energy of about 3.5 eV at 700 km. The total upward flux of hot oxygen atoms with energies higher 1 eV is estimated as 3.5 × 10[SUP]8[/SUP] cm[SUP]-2[/SUP] s[SUP]-1[/SUP]. [less ▲]

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See detailAuroral streamers and magnetic flux closure
Hubert, Benoît ULg; Kauristie, K.; Amm, O. et al

in Geophysical Research Letters (2007), 34(15),

On 7 December 2000 at 2200 UT an auroral streamer was observed to develop above Scandinavia with the IMAGE-FUV global imagers. The ionospheric equivalent current deduced from the MIRACLE-IMAGE ... [more ▼]

On 7 December 2000 at 2200 UT an auroral streamer was observed to develop above Scandinavia with the IMAGE-FUV global imagers. The ionospheric equivalent current deduced from the MIRACLE-IMAGE Scandinavian ground-based network of magnetometers is typical of a substorm-time streamer. Observations of the proton aurora using the SI12 imager onboard the IMAGE satellite are combined with measurements of the ionospheric convection obtained by the SuperDARN radar network to compute the dayside merging and nightside flux closure rates. On the basis of this and other similar events, it is found that auroral streamers appear during the period of most intense flux closure in the magnetotail, most often shortly after substorm onset. The ionospheric convection velocity, as measured by SuperDARN, appears to be reduced in the vicinity of the streamer, suggesting de-coupling of magnetospheric and ionospheric plasma flows in the region of enhanced ionospheric conductance. [less ▲]

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See detailAuroral ultraviolet emissions
Gérard, Jean-Claude ULg

in Physics and chemistry of atmospheres (1975)

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See detailL'Aurore des fanzineux
Capart, Philippe; Dejasse, Erwin ULg; Paques, Frédéric ULg

in Art&Fact (2012), 31

Detailed reference viewed: 19 (3 ULg)
See detailLes aurores boréales sur les planètes géantes. La « crise énergétique des planètes géantes »
Grodent, Denis ULg

Conference given outside the academic context (2011)

Les planètes géantes comme Jupiter et Saturne ont en commun une masse importante, l’absence de surface, une atmosphère dominée par l’hydrogène moléculaire et l’hélium ainsi qu'une grande variété ... [more ▼]

Les planètes géantes comme Jupiter et Saturne ont en commun une masse importante, l’absence de surface, une atmosphère dominée par l’hydrogène moléculaire et l’hélium ainsi qu'une grande variété d’hydrocarbures. Leur rotation rapide est à l'origine d'un champ magnétique particulièrement intense qui permet de transférer de grandes quantités d'énergie de la planète vers les particules ionisées qui les entourent. Cet échange s'effectue via des courants électriques extrêmement intenses qui, en interagissant avec l'atmosphère, provoquent des émissions aurorales. Nous décrirons des processus de précipitation d’électrons énergétiques dans l'atmosphère de Jupiter et nous nous intéresserons aux spectaculaires aurores polaires qui leur sont associées. Ces dernières seront illustrées par des images et animations obtenues dans l’ultraviolet à l’aide du Télescope Spatial Hubble. Nous montrerons comment les précipitations aurorales contrôlent dans une large mesure la température de la haute atmosphère de ces planètes et permettent de résoudre la « crise énergétique » des planètes géantes. [less ▲]

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See detailLes aurores dans le système solaire
Grodent, Denis ULg

Conference given outside the academic context (2002)

Detailed reference viewed: 3 (1 ULg)
See detailLes aurores de Jupiter et Saturne : la crise énergétique des planètes géantes
Grodent, Denis ULg

Conference given outside the academic context (2011)

Detailed reference viewed: 4 (0 ULg)
See detailAurores sur les planètes géantes
Bonfond, Bertrand ULg

Scientific conference (2011, December 08)

Depuis les premières détections d'émissions aurorales par les sondes Voyager à la fin des années 70, nos connaissances des aurores de Jupiter et de Saturne ont considérablement progressé. Je présenterai ... [more ▼]

Depuis les premières détections d'émissions aurorales par les sondes Voyager à la fin des années 70, nos connaissances des aurores de Jupiter et de Saturne ont considérablement progressé. Je présenterai ici quelques uns des derniers résultats obtenus à l'aide du télescope spatial Hubble et de la sonde Cassini en orbite autour de Saturne. Ces images acquises dans le domaine ultraviolet révèlent une complexité que l'on commence seulement à appréhender. Assemblées en séquences, elles dévoilent une dynamique surprenante. Flashs, pulsations, expansions, contractions, apparitions, disparitions, fusions, séparations et mouvements relatifs de structures étendues sur des dizaines de milliers de kilomètres ou localisés sur quelques centaines de kilomètres : la diversité des comportements que nous observons est le témoignage de la richesse des processus en œuvre dans les magnétosphères de Jupiter et Saturne. Lunes exotiques, volcans et geysers colossaux, champs magnétiques gigantesques et rotations planétaires rapides sont les ingrédients de ce surprenant laboratoire de physique des plasmas. [less ▲]

Detailed reference viewed: 19 (7 ULg)