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See detailAuroral Lyman alpha and H2 bands from the giant planets. 2: Effect of the anisotropy of the precipitating particles on the interpretation of the 'color ratio'
Prange, Renee; Rego, Daniel; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1995), 100

Previous spectral analyses have given evidence of collisionally excited Jovian and (at times) Saturnian H2 Werner bands being absorbed by hydrocarbons at the shortest wavelengths along the auroral ovals ... [more ▼]

Previous spectral analyses have given evidence of collisionally excited Jovian and (at times) Saturnian H2 Werner bands being absorbed by hydrocarbons at the shortest wavelengths along the auroral ovals, and of a longitudinal dependence of this absorption in the Jovian aurorae. This 'color ratio' has been used to estimate the energy of the primary particles. In such estimates, particles are generally assumed to penetrate vertically into the atmosphere. However, the precipitating particle angular distribution is unknown, and a model developed for a diffuse aurora by Prange and Elkhamsi (1991), for instance, predicts quite different possible distributions. We consider here the influence of the angular distribution used in the model, and show that distributions peaking far from vertical may increase the energy derived from a given color ratio by as much as a factor of 3. We discuss previous interpretations of the color ratio longitudinal modulation (variation of the auroral atmosphere structure, or of the incident particle energy) in view of the subsequent increase in energy input. We argue that an interpretation in terms of energy variations only is not consistent with the energy available in the magnetosphere if the aurorae are diffuse, and we discuss this finding in the context of recent Hubble Space Telescope (HST) images. [less ▲]

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See detailAuroral Lyman alpha and H2 bands from the giant planets: 1. Excitation by proton precipitation in the Jovian atmosphere
Rego, Daniel; Prange, Renee; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman-alpha and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident ... [more ▼]

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman-alpha and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident magnetospheric particle species and energy. The work is planned in three steps: (1) modeling of the volume excitation rate, (2) modeling of the radiative transfer at Lyman-alpha, (3) application to existing observational data and new data obtained from the Hubble Space Telescope. The present paper deals with the first step. Models of the volume excitation rate have previously been developed for low energy electrons and oxygen ions. However, the energy range of the study has to be extended towards higher energy in view of recent results on the penetration depth of the primary particles. Protons have not been modeled so far. We have used an existing electron code of degradation of energy (Gerard and Singh, 1982) which has been improved, updated and adapted to the case of precipitating protons. The issues of nonequilibrium beam H/H(+) fractions and of getting reliable cross sections over a wide energy range have been considered with particular care. The altitude distribution of the volume excitation rate is compared for electrons and protons, for various initial energies in the range 10-50 keV and 50 keV to 1 MeV, respectively. [less ▲]

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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: 36 (1 ULg)
See detailAuroral oval equatorward boundary during strong magnetic storms
Bojanowska, M.; Hubert, Benoît ULg; Nowakowski, R.

in 36th COSPAR Scientific Assembly (2006)

Data has been collected for selected strong magnetic storms during which auroras were seen from ground at middle- and low-latitudes as reported by amateur observers all over the world Auroral reports from ... [more ▼]

Data has been collected for selected strong magnetic storms during which auroras were seen from ground at middle- and low-latitudes as reported by amateur observers all over the world Auroral reports from ground were compared with auroral images from space Timed Image Polar and in situ measurements of plasma and magnetic electric fields in the disturbed inner magnetosphere A new version of the Weimer2005 electric potential model gives the boundary that defines the low-latitude edge of both the convection electric field and the magnetic perturbation due to the field-aligned currents We tried to find out whether it is possible to predict auroral oval position during strong magnetic storms using this improved ionospheric electrodynamic model A quite good compatibility between FAC pattern and oval position has been found This suggests that during strong magnetic storm Weimer2005 FAC model may be used to predict equatorward boundary of the auroral oval We also compared the observed low-latitude oval boundaries with projections of Alfven layer for plasma sheet electrons Particle trajectories were traced using T04 s magnetic field model and Weimer 2005 electric field model for given solar wind conditions Results will be discussed [less ▲]

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See detailAuroral polar dawn spots: Signatures of internally driven reconnection processes at Jupiter's magnetotail
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg 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 ▲]

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Peer Reviewed
See detailAuroral Precipitation during the Bastille Day Storm Recovery
Immel, T. J.; Mende, S. B.; Frey, H. U. et al

Conference (2001, December 01)

The recovery period following the geomagnetic storm of July 15-16, 2000 is marked by rapid changes in auroral morphology and brightness in the sunlit hemisphere. These observations are made by the FUV and ... [more ▼]

The recovery period following the geomagnetic storm of July 15-16, 2000 is marked by rapid changes in auroral morphology and brightness in the sunlit hemisphere. These observations are made by the FUV and EUV imagers aboard the IMAGE satelite. Clear signatures of magnetospheric convection are observed in the motion of the auroral forms, indicating sunward convection of plasma in the polar cap under the strong northward component of the IMF. Precipitation is also observed equatorward of the auroral oval on the dayside in large diffuse arcs. Unlike previously observed detached proton arcs, this precipitation appears to have a significant electron component. Determination of the characteristic energies and fluxes of electrons and protons requires the proper removal of FUV airglow emissions, which in this case have been strongly affected by the recent magnetic activity. EUV images provide a very clear signature of these events, with practically no airglow contamination. With proper modeling, these EUV images could provide improvements to the characterization of the magnetospheric energy input to the thermosphere and ionosphere from space-based imaging. [less ▲]

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See detailAuroral Processes
Kurth, W. S.; Bunce, E. J.; Clarke, J. T. et al

in Dougherty, M. K.; Esposito, L. W.; Krimigis, S. M. (Eds.) Saturn from Cassini-Huygens (2009)

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number ... [more ▼]

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number of campaigns were coordinated with the Hubble Space Telescope such that Cassini could provide either ground truth on the impinging solar wind or in situ measurements of magnetospheric conditions leading to qualitative and sometimes quantitative relationships between the solar wind influence on the intensity, the morphology and evolution of the auroras, and magnetospheric dynamics. The Hubble UV images are enhanced by Cassini’s own remote sensing of the auroras. Cassini’s in situ studies of the structure and dynamics of the magnetosphere discussed in other chapters of this book provide the context for understanding the primary drivers of Saturn’s auroras and the role of magnetospheric dynamics in their variations. Finally, Cassini’s three dimensional prime mission survey of the magnetosphere culminates in high inclination orbits placing it at relatively small radial distances while on auroral field lines, providing the first such in situ observations of auroral particles and fields at a planet other than Earth. The new observations have spawned a number of efforts to model the interaction of the solar wind with the magnetosphere and how such dynamics influence the auroras. [less ▲]

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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 ▲]

Detailed reference viewed: 26 (3 ULg)
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)

Detailed reference viewed: 16 (5 ULg)
See detailAuroral signatures of reconnection at Saturn and comparison with Earth
Radioti, Aikaterini ULg

Conference (2014, July)

Detailed reference viewed: 6 (1 ULg)
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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 ▲]

Detailed reference viewed: 6 (1 ULg)