References of "Radioti, Aikaterini"
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See detailSaturn's secondary auroral ring
Grodent, Denis ULg; Radioti, Aikaterini ULg; Bonfond, Bertrand ULg et al

Conference (2010)

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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 detailHow large is the Io UV footprint?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010)

Located close to the feet of the magnetic field lines connecting Io to each Jovian hemisphere, the Io footprint is the auroral signature of the electromagnetic interaction between Io and Jupiter's ... [more ▼]

Located close to the feet of the magnetic field lines connecting Io to each Jovian hemisphere, the Io footprint is the auroral signature of the electromagnetic interaction between Io and Jupiter's magnetosphere. It consists of several spots followed downstream by an extended tail. The size of the main spot is expected to scale to the size of the interaction region close to Io. Consequently, this quantity is crucial to understand the processes involved. However, the main spot size is a controversial issue as previously published values range from ~400 km to ~10000 km, leading to contradictory conclusions. Based on observations carried on with the Hubble Space Telescope STIS and ACS FUV instruments from 1997 to 2009, we estimate the size of the main footprint spot on a much larger image sample than previously. Additionally, we carefully selected the images in order to avoid viewing geometry ambiguities when measuring the spatial extent of the different features. The main spot length along the footpath is ~900 km while its width perpendicular to the footpath is <200 km. The spot length is larger than the projected diameter of Io along unperturbed magnetic field lines, which appears to be consistent with recent simulations. The vertical extent and the peak altitude of the main spot are similar to those measured in the tail. Nevertheless, the secondary spot attributed to trans-hemispheric electron beams has been measured to peak at ∼200 km below the main spot and the tail, which confirms their different origins. [less ▲]

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See detailHow bright is the Io UV footprint?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010)

The electro-magnetic interaction between Io and the Jovian magnetosphere generates a perturbation in the magnetospheric plasma which propagates along the magnetic field lines and creates auroral footprint ... [more ▼]

The electro-magnetic interaction between Io and the Jovian magnetosphere generates a perturbation in the magnetospheric plasma which propagates along the magnetic field lines and creates auroral footprint emissions in both hemispheres. Recent results showed that this footprint is formed of several spots and an extended tail. Each feature is suggested to correspond to a different step in the propagation of the perturbation and in the electron energization processes. The present study focuses on the variations of the spots' brightness at different timescales from minutes to years through the rotation period of Jupiter. It relies on FUV images acquired with the STIS and ACS instruments onboard the Hubble Space Telescope. Since the footprint is composed of several localized features, a good understanding of the emission region geometry is critical to derive the actual vertical brightness and thus the precipitated energy flux. We developed a 3D emission model in order to assess as precisely as possible the respective contribution of each individual feature and to correctly estimate the precipitating energy flux. As far as the brightness variations on timescales of minutes are concerned, we will present results from the high time resolution campaign executed during summer 2009. On timescale of several hours, we will show that the variation of the emitted power as a function of the location of Io in the plasma torus suggests that the Jovian surface magnetic field strength is an important controlling parameter. Finally, the measured precipitated power and particle fluxes will be discussed in comparison with recent simulations considering both Alfvén waves filamentation and electron acceleration when the Alfvén waves become inertial. [less ▲]

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See detailSaturn's polar auroral emissions
Radioti, Aikaterini ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2010)

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See detailThe very busy auroral footprint of Ganymede
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2009, September 13)

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See detailJupiter's ultraviolet polar auroral emissions
Coumans, Valérie ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2009, September)

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See detailThe auroral footprint of Ganymede
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114(A07212),

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede ... [more ▼]

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede footprint. Based on an analysis of ultraviolet images obtained with the Hubble Space Telescope we demonstrate that the auroral footprint surface matches a circular region in Ganymede's orbital plane having a diameter of 8 to 20 RG. Temporal analysis of the auroral power of Ganymede's footprint reveals variations of different timescales: 1) a 5 hours timescale associated with the periodic flapping of Jupiter's plasma sheet over Ganymede, 2) a 10 to 40 minutes timescale possibly associated with energetic magnetospheric events, such as plasma injections, and 3) a 100 s timescale corresponding to quasi-periodic fluctuations which might relate to bursty reconnections on Ganymede's magnetopause and/or to the recurrent presence of acceleration structures above Jupiter's atmosphere. These three temporal components produce an auroral power emitted at Ganymede's footprint of the order of ~0.2 GW to ~1.5 GW. [less ▲]

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See detailThe Io UV footprint: Location, inter-spot distances and tail vertical extent
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by ... [more ▼]

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by an auroral curtain, called the tail, extending more than 90° longitude in the direction of planetary rotation. We use recent Hubble Space Telescope images of Jupiter to analyze the location of the footprint spots and tail as a function of Io's location in the jovian magnetic field. We present here a new IFP reference contour---the locus of all possible IFP positions---with an unprecedented accuracy, especially in previously poorly covered sectors. We also demonstrate that the lead angle - the longitudinal shift between Io and the actual IFP position - is not a reliable quantity for validation of the interaction models. Instead, the evolution of the inter-spot distances appears to be a better diagnosis of the Io-Jupiter interaction. Moreover, we present observations of the tail vertical profiles as seen above the limb. The emission peak altitude is ~900 km and remains relatively constant with the distance from the main spot. The altitudinal extent of the vertical emission profiles is not compatible with precipitation of a mono-energetic electron population. The best fit is obtained for a kappa distribution with a characteristic energy of ~70 eV and a spectral index of 2.3. The broadness of the inferred electron energy spectrum gives insight into the physics of the electron acceleration mechanism at play above the IFP tail. [less ▲]

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See detailCorrection to ``Equatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations''
Radioti, Aikaterini ULg; Tomás, Ana Tomas; Grodent, Denis ULg et al

in Geophysical Research Letters (2009), 36

<A href="/journals/gl/gl0909/2009GL038676/">Abstract Available</A> from <A href="http://www.agu.org">http://www.agu.org</A>

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See detailEquatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations
Radioti, Aikaterini ULg; Tomás, Ana Teresa; Grodent, Denis ULg et al

in Geophysical Research Letters (2009), 36

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes ... [more ▼]

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes in the electron pitch angle distribution between the inner and middle magnetosphere (PAD boundary), indicative of electron diffusion. This region, magnetically maps to the equatorward diffuse emissions on both hemispheres. Whistler mode waves, observed simultaneously, can scatter electrons into the loss cone and lead to electron precipitation in the ionosphere. Based on simultaneous HST FUV and Galileo wave and electron data we test the conditions for electron scattering by whistler mode waves and derive the energy flux precipitated in the ionosphere. The comparison of the derived precipitation energy flux with the observed auroral brightness indicates that the energy contained in the PAD boundary can account for the auroral emissions. [less ▲]

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See detailTransient auroral features at Saturn: Signatures of energetic particle injections in the magnetosphere
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114

We report for the first time transient isolated auroral spots at Saturn's southern polar region, based on Hubble Space Telescope (HST) FUV images. The spots last several minutes and appear distinct from ... [more ▼]

We report for the first time transient isolated auroral spots at Saturn's southern polar region, based on Hubble Space Telescope (HST) FUV images. The spots last several minutes and appear distinct from the rest of the auroral emissions. We study two sets of HST and Cassini observations during which Cassini instrumentation detected signatures of energetic particle injections close to the region where, on the same day, HST observed transient auroral spots. On the basis of the simultaneous remote and in situ observations, we discuss the possibility that the transient features are associated with the dynamical processes taking place in the Kronian magnetosphere. Given the limitations in the available observations, we suggest the following possible explanations for the transient aurora. The injection region could directly be coupled to Saturn's ionosphere by pitch angle diffusion and electron scattering by whistler waves, or by the electric current flowing along the boundary of the injected cloud. The energy contained in the injection region indicates that electron scattering could account for the transient aurora process. [less ▲]

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See detailRecent results from HST and ground-based observations of Saturn's aurora
Grodent, Denis ULg; Stallard, T.; Gérard, Jean-Claude ULg et al

Conference (2008, December 01)

Current observations of Saturn's aurora performed from Earth-orbit with HST and ground based instruments more than complement the in situ measurements obtained by the Cassini spacecraft. These remote ... [more ▼]

Current observations of Saturn's aurora performed from Earth-orbit with HST and ground based instruments more than complement the in situ measurements obtained by the Cassini spacecraft. These remote observations focus on two spectral windows revealing different facets of the same auroral phenomenon. The auroral photons captured in the ultraviolet bandwidth result from direct impact excitation of H and H2 by charged particles accelerated along magnetic field lines, while the thermal infrared emission involves additional steps in order to produce hot H3+ from the auroral energy. Each spectral window presents its own advantages. The high spatial and temporal resolution of the recent UV images obtained with HST make it possible to discriminate auroral sub-structures, such as short lived arcs and spots, and to map them into the magnetosphere where they can be associated with in situ observations. Infrared high resolution spectroscopy and emission-line imaging from ground observatories (IRTF, UKIRT) have more modest spatial resolution; however they recently pinned down emissions barely observed in the UV. Furthermore, they offer a direct measurement of the ion wind velocities in the auroral ionosphere. These ion flow patterns might then be used to untangle the origin of the auroral particles. The complementarity of observations obtained in the UV and IR bandwidths provides a powerful tool to study the auroral mechanisms in the Kronian magnetosphere and the atmospheric response to the auroral input. [less ▲]

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See detailLong-term Brightness Variations of the Io UV Footprint
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2008, December 01)

Since the finding of the UV Io footprint in 1996, the successive UV instruments on board the Hubble Space Telescope (HST) allowed us to considerably improve the understanding of the Io-Jupiter electro ... [more ▼]

Since the finding of the UV Io footprint in 1996, the successive UV instruments on board the Hubble Space Telescope (HST) allowed us to considerably improve the understanding of the Io-Jupiter electro-magnetic interaction and its auroral counterpart. It has been shown that the Io footprint is generally formed by one bright spot preceded or followed by secondary spots whose relative positions are linked to the location of Io in the plasma torus. We also know that these spots experience brightness variations from minutes to hours. The Io footprint brightness varies over hours with the longitude of Io in the Jovian magnetic field (System III longitude) but until recently, huge gaps existed in the longitude coverage. Part of these gaps has now been filled during the latest HST imaging campaign and a more complete spot brightness versus Io System III longitude diagram emerges. Additionally, we compare spot brightness between images obtained a few minutes apart but from opposite hemispheres. Based on images gathered from 1997 to 2007 with the STIS and the ACS cameras, we also show that the footprint morphology and the spots brightness, including their relative brightness, can vary significantly from one year to another. Finally, we discuss the brightness variations from hours to years in terms of plasma torus density and position of Io in the plasma torus as well as in Jovian magnetic field. [less ▲]

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See detailJupiter’s main auroral emission; local time and temporal variability
Grodent, Denis ULg; Radioti, Aikaterini ULg; Bonfond, Bertrand ULg et al

Conference (2008, September 23)

Jupiter's main auroral oval is associated with the ionosphere-magnetosphere coupling current system which is related to the breakdown of corotation in the middle magnetosphere. Its auroral footpath is ... [more ▼]

Jupiter's main auroral oval is associated with the ionosphere-magnetosphere coupling current system which is related to the breakdown of corotation in the middle magnetosphere. Its auroral footpath is usually represented as a smooth line closing around the pole. However, this simplistic view is misleading in many regards. We have constructed a new reference contour in the northern hemisphere (Figure 1), based on more than 1000 HST/UV images, which does not look like an oval and does not close around the pole. We use this reference contour to quantify the effects of temporal and local time variability of the magnetospheric plasma characteristics on the location of the main auroral emission. Beyond the orbit of Ganymede (15RJ), two key ingredients are expected to have a measurable influence on the instantaneous shape of the main emission contour: the azimuthal current flowing in the current sheet [1,2] and the corotation breakdown distance. The former affects the radial extent of the magnetic field lines, and the latter determines the radial location of the field aligned currents transmitting momentum from the planet to the lagging plasma. So far, models used to magnetically map the auroral main emission between the ionosphere and the equatorial plane assumed that these two parameters are constant and axisymmetric. However, in situ observations, mainly by Galileo, have revealed large local time asymmetries and temporal variations in the plasma flows and distribution. These variations have an impact on the azimuthal current and the distance at which the plasma angular velocity becomes significantly smaller than planetary rotation. We use a new magnetic field model [3], inherited from VIP4 and including a magnetic anomaly in the northern hemisphere, to simulate the effects of these asymmetries on the location of the main auroral emission, and interpret the large scattering of the corresponding HST data point. [less ▲]

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