References of "Radioti, Aikaterini"
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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 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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See detailAuroral emission at Jupiter, through Juno's UVS eyes
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gladstone, G. et al

Conference (2015, June 02)

Juno’s orbit insertion around Jupiter will take place in little bit more than one year (July 2016). After a 107-day capture orbit (Oct. 2016), it will perform a series of 33 eleven-day science polar ... [more ▼]

Juno’s orbit insertion around Jupiter will take place in little bit more than one year (July 2016). After a 107-day capture orbit (Oct. 2016), it will perform a series of 33 eleven-day science polar orbits offering unprecedented views of the auroral regions of Jupiter. The science payload of Juno includes an UltraViolet Spectrograph (UVS) that will characterize the UV auroral emissions of Jupiter over all science orbits. It will obtain high-resolution images and spectra that will provide context for Juno’s in situ particles and fields measurements in the larger polar magnetosphere with Juno’s JADE and JEDI detectors. At the same time, the MAG instrument will accurately constrain magnetic field models, which will provide the connection between Juno and its field line footprint in the Jovian aurora. The UVS instrument consists of a solar blind MCP detector with a “dog-bone” shape FOV of 0.2°x2.5°+0.025°x2°+0.2°x2.5° providing a spatial resolution of 125 km from 1RJ above the aurora and a spectral resolution of ~0.5 nm (~2 nm for extended sources). It is sensitive to EUV-FUV radiation ranging from 70 nm to 205 nm. Juno is a spin-stabilized spacecraft and is rotating at a frequency of 2 RPM. UVS will take advantage of this motion to scan the auroral regions in the direction perpendicular to the slit, while its steerable pickup mirror (±30° from the spin plane) will make it possible to point at specific regions of the aurora. Juno’s highly eccentric science orbits have a perijove close to 1.05 RJ (~5000 km above cloud deck) and an apojove at ~38 RJ. These orbits approximately lie in the Dawn meridian plane and are such that each successive pass is at a Jovian longitude displaced by 204° from the previous perijove. At perijove, Juno’s velocity will be ~60 km/s and about 20 km/s above the poles, meaning that the spacecraft will move over the northern and southern auroral regions in approximately two hours. In this study, we are using existing HST STIS time-tag sequences of Jupiter’s UV aurorae in order to simulate the expected measurements through UVS FOV along Juno’s predicted trajectory. The simulations account for realistic instrumental specifications and pointing and for the temporal and spatial variability of the aurora. We show the results of image reconstruction obtained from scanning the auroral region with UVS slit and provide some limits on the expected data quality as a function of the location of Juno along its orbit. We also suggest portions of the science orbits for which supporting HST observations will be necessary. [less ▲]

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See detailSearch for Satellite Effects on Saturn's Auroras in Cassini UVIS Data
Pryor, Wayne; Espositio, Larry; Jouchoux, Alain et al

Poster (2015, June)

The Cassini Ultraviolet Imaging Spectrograph (UVIS) has been obtaining Saturn auroral images since 2004. We have previously reported instances when the main auroral oval brightened briefly in a quasi ... [more ▼]

The Cassini Ultraviolet Imaging Spectrograph (UVIS) has been obtaining Saturn auroral images since 2004. We have previously reported instances when the main auroral oval brightened briefly in a quasi-periodic fashion near the sub-Mimas longitude. Here we examine the large set of UVIS auroral images obtained from close range and high sub-spacecraft latitudes. We will plot the brightness of the individual auroral measurements (and binned auroral measurements) as a function of local time, and as a function of the location of Mimas and other moons to test for any correlations. Mimas, while a relatively small moon, exerts a strong influence on Saturn's ring system. Mimas creates the Cassini Division between the A and B rings and forces a non-circular shape to the outer edge of Saturn's B ring that is partially locked to Mimas phase. [less ▲]

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See detailJupiter's equatorward auroral features
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2015, May 13)

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See detailMagnetosphere-ionosphere mapping at Jupiter: Quantifying the effects of using different internal field models
Vogt, Marissa; Bunce, Emma; Kivelson, Margaret et al

in Journal of Geophysical Research. Space Physics (2015), 120

The lack of global field models accurate beyond the inner magnetosphere (<30 RJ) makes it difficult to relate Jupiter's polar auroral features to magnetospheric source regions. We recently developed a ... [more ▼]

The lack of global field models accurate beyond the inner magnetosphere (<30 RJ) makes it difficult to relate Jupiter's polar auroral features to magnetospheric source regions. We recently developed a model that maps Jupiter's equatorial magnetosphere to the ionosphere using a flux equivalence calculation that requires equal flux at the equatorial and ionospheric ends of flux tubes. This approach is more accurate than tracing field lines in a global field model but only if it is based on an accurate model of Jupiter's internal field. At present there are three widely used internal field models—Voyager Io Pioneer 4 (VIP4), the Grodent Anomaly Model (GAM), and VIP Anomaly Longitude (VIPAL). The purpose of this study is to quantify how the choice of an internal field model affects the mapping of various auroral features using the flux equivalence calculation. We find that different internal field models can shift the ionospheric mapping of points in the equatorial plane by several degrees and shift the magnetospheric mapping to the equator by ~30 RJ radially and by less than 1 h in local time. These shifts are consistent with differences in how well each model maps the Ganymede footprint, underscoring the need for more accurate Jovian internal field models. We discuss differences in the mapping of specific auroral features and the size and location of the open/closed field line boundary. Understanding these differences is important for the continued analysis of Hubble Space Telescope images and in planning for Juno's arrival at Jupiter in 2016. [less ▲]

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See detailIn Overview of the Auroras of Jupiter and Saturn from the Cassini Perspective (Invited)
Pryor; Esposito; Jouchoux et al

Conference (2015)

The Cassini spacecraft flew by Jupiter in late 2000 and early 2001 and has been orbiting Saturn since 2004. A highlight of the mission has been an unprecedented collection of high-resolution auroral ... [more ▼]

The Cassini spacecraft flew by Jupiter in late 2000 and early 2001 and has been orbiting Saturn since 2004. A highlight of the mission has been an unprecedented collection of high-resolution auroral images of Saturn obtained in the visible by Cassini ISS, in the infrared by Cassini VIMS, and in the ultraviolet by Cassini UVIS. We will briefly discuss auroral observations of Jupiter by Cassini showing auroral storms and episodes of periodic pulsations, then highlights from the large database of Saturn auroral images and movies, and complementary fields and particles data. Complementary and sometimes simultaneous HST images will also be shown. Saturn's auroras exhibit a wide variety of changing forms. At times multiple narrow arcs are seen, at other times a single broader emission is seen. The polar cap inside the oval exhibits changing discrete forms, often near noon local time in the polar cusp region. Satellite footprints associated with Enceladus are very rarely seen. Bright auroral pulsations on the main oval sometimes occur, separated by about an hour. At times these seem associated with the moon Mimas, occurring at the sub-Mimas longitude and moving with the moon. We indicate a possible mechanism for this, involving Mimas control of the width of the Cassini Division, which forms a channel for plasma flow connecting Saturn's rings and/or flowing through Saturn's rings. [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 (2015)

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See detailAuroral spirals at Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2015)

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See detailConcurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Libert, Ludivine ULg et al

in Journal of Geophysical Research. Space Physics (2015)

The database of the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument between late January 2004 and Mars 2014 has been searched to identify signatures ... [more ▼]

The database of the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument between late January 2004 and Mars 2014 has been searched to identify signatures of CO Cameron and CO<inf>2</inf>+ doublet ultraviolet auroral emissions. This study has almost doubled the number of auroral detections based on SPICAM spectra. Auroral emissions are located in the vicinity of the statistical boundary between open and closed field lines. From a total of 113 nightside orbits with SPICAM pointing to the nadir in the region of residual magnetic field, only nine nightside orbits show confirmed auroral signatures, some with multiple detections along the orbital track, leading to a total of 16 detections. The mean energy of the electron energy spectra measured during concurrent Analyzer of Space Plasma and Energetic Atoms/Electron Spectrometer observations ranges from 150 to 280eV. The ultraviolet aurora may be displaced poleward or equatorward of the region of enhanced downward electron energy flux by several tens of seconds and shows no proportionality with the electron flux at the spacecraft altitude. The absence of further UV auroral detection in regions located along crustal magnetic field structures where occasional aurora has been observed indicates that the Mars aurora is a time-dependent feature. These results are consistent with the scenario of acceleration of electrons by transient parallel electric field along semiopen magnetic field lines. © 2015. American Geophysical Union. All Rights Reserved. [less ▲]

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