References of "Radioti, Aikaterini"
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See detailJupiter’s magnetopause: A search for reconnection and wave signatures
Bonfond, Bertrand ULg; Kivelson, Margaret; Khurana, Krishan et al

Conference (2016, April 26)

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See detailPlanetary Space Weather: Scientific Aspects and Future Perspectives
Plainaki, C.; Lilensten, J.; Radioti, Aikaterini ULg et al

in Journal of Space Weather and Space Climate (2016)

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See detailThe color ratio-intensity relation in the Jovian aurora: Hubble observations of auroral components
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

in Planetary and Space Science (2016), 131

Spectral observations made with the long slit of the Space Telescope Imaging Spectrograph (STIS) on board Hubble have been used to construct spectral maps of the FUV Jovian aurora. They reveal that the ... [more ▼]

Spectral observations made with the long slit of the Space Telescope Imaging Spectrograph (STIS) on board Hubble have been used to construct spectral maps of the FUV Jovian aurora. They reveal that the amount of absorption by overlying methane shows significant spatial variations. In this report, we examine the relationship between the auroral brightness of the unabsorbed H2 emission that is proportional to the precipitated electron energy flux, and the ultraviolet color ratio, a proxy of the mean electron energy. We find that it varies significantly between the different components of the aurora and in the polar region. Although no global dependence can be found, we show that the two quantities are better organized in some auroral components such as regions of the main aurororal emission. By contrast, the dependence of the electron characteristic energy in high-latitude and diffuse aurora regions on the auroral energy input is generally more scattered. We conclude that the various auroral components are associated with different electron acceleration processes, some of which are not governed by a simple relation linking the value of a field-aligned acceleration potential with the parallel currents flowing from the ionosphere. [less ▲]

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See detailHST-Juno synergistic approach of Jupiter's magnetosphere and ultraviolet auroras
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg et al

E-print/Working paper (2016)

Jupiter's system is not only fundamental to our understanding of the solar system but also of planetary systems around other stars as well as more distant astrophysical bodies, not accessible to a ... [more ▼]

Jupiter's system is not only fundamental to our understanding of the solar system but also of planetary systems around other stars as well as more distant astrophysical bodies, not accessible to a detailed investigation. Fully exploiting any rare opportunity to explore the Jovian system through synergistic observations is thus critical, as it will impact significantly across wider astronomical studies. Such an exceptional opportunity will occur in Cycle 24, when the NASA Juno spacecraft will achieve its prime mission around Jupiter. Since Juno will literally fly through the auroral acceleration regions, the combination of HST auroral observations with Juno in situ measurements will allow us to finally unravel the origins and consequences of Jupiter's powerful and highly variable ultraviolet auroras. This occasion has never occurred before and is unlikely to ever repeat. Juno will address key scientific issues related to unexplored regions of the Jovian magnetosphere. The auroral signatures associated with these magnetospheric processes will be precisely observed with STIS and COS. This program responds to the UV initiative and is only possible during Cycle 24. Indeed, HST is the only observatory capable of making these high spatial and temporal resolution FUV observations during the Juno mission. This ambitious campaign will yield high-impact results and significantly augment the science return of the NASA Juno mission. [less ▲]

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See detailCassini in situ observations of long duration magnetic reconnection in Saturn’s magnetotail
Arridge, C.S.; Eastwood, J.P.; Jackman, C.M. et al

in Nature (2016)

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See detailSimultaneous multi-scale and multi-instrument observations of Saturn's aurorae during the 2013 observing campaign
Melin, H.; Badman, S.; Stallard, T. et al

in Icarus (2016)

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See detailRecurrent pulsations in Saturn’s high latitude magnetosphere
Mitchell, D.G.; Carbary, J.F.; Bunce, E.J. et al

in Icarus (2016)

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See detailSaturn’s auroral morphology and field-aligned currents during a solar wind compression
Badman, S.V.; Provan, G.; Bunce, E.J. et al

in Icarus (2016)

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See detailUltraviolet auroral emissions on giant planets
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2015, November 25)

The aurorae on Jupiter and Saturn are the most powerful proper ultraviolet emissions in our solar system, after the Sun’s. They can only be observed outside the absorbing atmosphere of the Earth with ... [more ▼]

The aurorae on Jupiter and Saturn are the most powerful proper ultraviolet emissions in our solar system, after the Sun’s. They can only be observed outside the absorbing atmosphere of the Earth with space telescopes such as the Hubble Space Telescope or the Hisaki Telescope, or from Spacecraft orbiting these planets, like Cassini for Saturn and Juno for Jupiter. We will review the types of observation that can be obtained with these different instruments and how this information can be used to interpret the auroral emissions. [less ▲]

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See detailThe far-ultraviolet main auroral emission at Jupiter – Part 1: Dawn–dusk brightness asymmetries
Bonfond, Bertrand ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

in Annales Geophysicae (2015), 33

The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted ... [more ▼]

The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ~ 3 times brighter than the dawn side in the southern hemisphere and ~ 1.1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements. We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere. [less ▲]

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See detailThe far-ultraviolet main auroral emission at Jupiter – Part 2: Vertical emission profile
Bonfond, Bertrand ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

in Annales Geophysicae (2015), 33

The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as ... [more ▼]

The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as it accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range. The energy of the precipitating electrons is a crucial parameter to characterize the processes at play which give rise to these auroral emissions, and the altitude of the emissions directly depends on this energy. Here we make use of far-UV (FUV) images acquired with the Advanced Camera for Surveys on board the Hubble Space Telescope and spectra acquired with the Space Telescope Imaging Spectrograph to measure the vertical profile of the main emissions. The altitude of the brightness peak as seen above the limb is ~ 400 km, which is significantly higher than the 250 km measured in the post-dusk sector by Galileo in the visible domain. However, a detailed analysis of the effect of hydrocarbon absorption, including both simulations and FUV spectral observations, indicates that FUV apparent vertical profiles should be considered with caution, as these observations are not incompatible with an emission peak located at 250 km. The analysis also calls for spectral observations to be carried out with an optimized geometry in order to remove observational ambiguities. [less ▲]

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See detailDynamics of the active region in Jupiter’s aurorae
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2015, September 29)

The Far-UV aurorae at Jupiter variety on a wide range of timescales. This study focuses on the dynamics of the active region on timescales of a few minutes. Up to now, only the time-tag mode of the Space ... [more ▼]

The Far-UV aurorae at Jupiter variety on a wide range of timescales. This study focuses on the dynamics of the active region on timescales of a few minutes. Up to now, only the time-tag mode of the Space Telescope Imaging Spectrograph provides access to such fast variations with a high spatial resolution. This active region, located on the dusk flank of the area inside the main auroral oval, is the locus of particularly bright (up to several mega Reyleighs) and sudden (a few tens of seconds) enhancements called flares. A previous study also showed that these flare could reoccur quasi-periodically every 2-3 minutes and propagate from dusk to dawn. Here we use data obtained in 2013 and 2014 to show that this quasi-periodic behavior is only present on half of the cases and that the affected region could either cover the whole active region or a much smaller area (∼5000km^2). We also found areas that were still during part of the observation sequence and then began to blink (see Figure 1). We also show that there no systematically preferred propagation direction. Finally, sequences acquired successively in the two hemispheres show that the quasi-periodic flares can be in phase [less ▲]

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See detailSimulations of the auroral signatures of Jupiter’s magnetospheric injections
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2015, September 29)

We report the evolution of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images of the northern and the southern Jovian hemisphere. We ... [more ▼]

We report the evolution of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images of the northern and the southern Jovian hemisphere. We investigate the possibility that those ultraviolet auroral structures are associated with energetic particle injections. For this study, we compare the characteristics of the simulated auroral signature of plasma injections with the observed parameters of equatorward isolated auroral structures. [less ▲]

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See detailSolar wind interaction with the terrestrial planets
Garnier, P.; Milillo, A.; Radioti, Aikaterini ULg

in Planetary and Space Science (2015)

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See detailSimulations of the auroral signatures of Jupiter’s magnetospheric injections
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Poster (2015, June 04)

Jupiter’s ultraviolet auroral emissions are divided into four main components: the polar emissions, the main emission, the satellite footprints and the outer emissions. The morphology of the outer ... [more ▼]

Jupiter’s ultraviolet auroral emissions are divided into four main components: the polar emissions, the main emission, the satellite footprints and the outer emissions. The morphology of the outer emissions can be either diffuse, arc-shaped or compact emissions. In the present study, we focus on outer emissions clearly detaching from the main emission and forming compact structures that are evolving regardless of the rest of the auroral emission. These auroral features were selected because they have the same appearance as the auroral signature of a clearly identified injection previously observed by Mauk et al. [2002] at Jupiter, based on simultaneous Galileo spacecraft and Hubble Space Telescope measurements. Here, we report on the evolution of those ultraviolet auroral features appearing in Hubble Space Telescope images of the northern and southern Jovian hemispheres. We investigate the possibility that those ultraviolet auroral structures are associated with energetic particle injections. For this study, we analyze the temporal variations of the longitudinal extent and of the brightness of the auroral structures. Indeed, the injected charged particles drift at different rates due to energy-dependent gradient and curvature drifts, which leads to an increase with time of the longitudinal extent of the feature and of its associated auroral signature. Since the injected energy follows the same trend, the brightness decreases with time. Different processes can generate auroral signatures of plasma injections. We simulate them by considering that pitch angle diffusion is generated by the precipitating energy flux in the ionosphere and whistler-mode waves through electron scattering. We compare the characteristics of the simulated signature with the observed parameters. Following this comparison, we are able to test whether the aforementioned mechanism is responsible for the auroral emission and to infer the typical energy and the spectral index of the energy distribution of the electrons involved in the injection process. [less ▲]

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See detailThe Main Auroral Emission at Jupiter: Altitude profile and Dawn-Dusk Asymmetry
Bonfond, Bertrand ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

Poster (2015, June 04)

The main auroral emission at Jupiter generally forms a quasi-continuous curtain around each magnetic poles. This emission magnetically maps to the middle magnetosphere and is related to the corotation ... [more ▼]

The main auroral emission at Jupiter generally forms a quasi-continuous curtain around each magnetic poles. This emission magnetically maps to the middle magnetosphere and is related to the corotation enforcement of the plasma originating from the volcanic satellite Io. The first models of corotation enforcement current system at Jupiter assumed symmetry around the magnetic axis. However, observations and further development of these models outlined the importance of local time variability of such currents. In this presentation, we show the results of two studies of this local time variability relying on the large dataset of Far-UV observations from the Hubble Space Telescope (HST). Knight’s theory of field aligned current predicts that the auroral precipitating energy flux and the energy of the precipitating electrons are correlated. Since the altitude of the auroral emissions decreases as the energy increases, it is thus expected that the altitude of the auroral brightness peak varies as a function of the local time following the variations of the field aligned currents. We compare the altitude of the main emission on the post-dusk side as seen in the visible domain by Galileo’s Solid State Imager and the same altitude for the night side as seen by the Advanced Camera for Surveys (ACS) on board HST in the Far-UV domain. We show some significant differences between the two data sets. Unfortunately, a careful analysis involving both spectral observations and simulations indicates that the Far-UV vertical profiles are hampered by observational ambiguities due to absorption by hydrocarbon molecules. Only additional and judiciously designed new observations could reveal the actual amount of methane along the line of sight. The second study consists in a comparison of the emitted power in local time sectors corresponding to dawn and dusk. Results in the northern hemisphere are difficult to interpret because the magnetic anomaly probably causes a decrease of the auroral brightness in regions of strong magnetic field. In the southern hemisphere, where the field magnitude is more uniform along the main oval, the dusk sector is ~3 times brighter than the dawn sector. In accordance with measurements of magnetic field divergence in the equatorial plane by Galileo, these results suggest the presence of a partial ring current in the night side of the magnetosphere with upward currents in the dawn side and downward currents in the dusk side. [less ▲]

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See detailHubble spectral observations of the Jovian aurora: precipitated flux and electron mean energy
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2015, June 02)

The FUV Jovian aurora is excited by collisions of energetic electrons accelerated along the magnetic field lines with the ambient upper atmosphere. The emission is dominated by the H2 Lyman and Werner ... [more ▼]

The FUV Jovian aurora is excited by collisions of energetic electrons accelerated along the magnetic field lines with the ambient upper atmosphere. The emission is dominated by the H2 Lyman and Werner bands extending from the extreme ultraviolet to about 170 nm. The wavelengths below about 135 nm are partly absorbed by the methane layer overlying the auroral emission layer. The long wavelength intensity is proportional to the precipitated energy flux carried by the auroral electrons. Spectral observations with the Hubble Space Telescope were made in 2014 using the long slit of the Space Telescope Imaging Spectrograph (STIS) in the timetag mode. During these observations, the slit projection scanned the polar region down to mid-latitudes. The combination of spectral and temporal measurements was used to build up the first spectral maps of the FUV Jovian aurora. The two-dimensional distribution of the intensity ratio of the two spectral regions has been obtained by combining spectral emissions in these wavelength ranges. They show that the amount of absorption by methane varies significantly between the different components of the aurora and in the polar region. Outputs from an electron transport model are used to create maps of the distribution of the characteristic electron energies. Using model atmospheres adapted to auroral conditions, we conclude that electron energies generally range between a few tens to several hundred keV. In this presentation, we analyze the relationship between the precipitated electron energy flux and the mean electron energy derived from these observations. Although globally, no correlation can be found, we show that the two quantities co-vary in some auroral components such as in the morning sector or in the striations observed along the main emission. By contrast, the auroral input in some high-latitude regions show no correlation with the electron characteristic energy. These aspects will be quantitatively discussed and possible processes explaining this dichotomy will be proposed. Comparisons of derived energies are in general agreement with those calculated from magnetosphere-ionosphere coupling models, but they locally exceed current model predictions. These results provide a basis for three-dimensional modeling of the distribution of particle heat sources into the high-latitude Jovian upper atmosphere. [less ▲]

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