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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 detailConnecting planets to their moons: The auroral satellite footprints
Bonfond, Bertrand ULg

Conference (2015, June 03)

Among the many features of the Giant planets’ aurorae are very special spots which move in a very distinct manner compared with the remaining of the aurora. Indeed, these spots are magnetically connected ... [more ▼]

Among the many features of the Giant planets’ aurorae are very special spots which move in a very distinct manner compared with the remaining of the aurora. Indeed, these spots are magnetically connected with planetary satellites and rotate around the poles at the same pace as their parent moon. These features, called the satellite footprints, are the signature of the electromagnetic interaction between the moons and the rapidly rotating magnetosphere plasma. On Jupiter, Io, Europa and Ganymede (and possibly Callisto) have their respective footprints while only the Enceladus footprint has been detected on Saturn so far. Several models of the interaction between Io and the jovian magnetosphere, from the unipolar inductor to the ideal Alfvén wings model, have been proposed well before the first observations of the footprints in 1993. However, the continuously improving technologies and observing methods gave rise to more accurate observations that challenged several aspects of these models and lead to further refinements. For example, when analyzed in detail, high resolution images of the aurorae show that the footprints of Io and Ganymede are not made of one, but several spots, and that the footprint of Io, Europa and Ganymede can be followed by an extended tail. The respective motion of these spots as a function of the orientation of the planetary magnetic field suggests that the Alfvén waves launched from these satellites accelerate the electrons in both directions along the field lines, hence doubling the number of visible spots, Moreover, studies of the satellite footprints are not only useful to unveil some key aspects of the moon-magnetosphere interactions, but they also contribute to the understanding of the whole magnetospheric system. For instance, their locations have been used as landmarks to constrain magnetic field models or to more accurately relate some auroral structures with their root region in the magnetosphere. [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 detailFrom the Hubble Space Telescope to Juno, unraveling the secrets of Jupiter's UV aurorae
Bonfond, Bertrand ULg

Conference (2015, May 19)

The successive generations of instruments on board the Hubble Space Telescope (HST) have revealed an increasing amount of details concerning the aurorae of Jupiter. Among the most striking results is the ... [more ▼]

The successive generations of instruments on board the Hubble Space Telescope (HST) have revealed an increasing amount of details concerning the aurorae of Jupiter. Among the most striking results is the finding that these aurorae are actually made of a multitude of components arising from a variety of processes, ranging from the local interaction of the Jovian moons with the magnetospheric plasma to solar-wind induced compression of the whole magnetosphere. In this presentation, I will review a few recent results obtained from Hubble Space Telescope observations. First, I will show how the morphology and the dynamics of the Ganymede footprint, i.e. the aurora on Jupiter created by the electromagnetic interaction between Ganymede and Jupiter, allowed us to infer the processes at play. Then, I will present results on the vertical profile of the auroral emissions and what they tell us about the acceleration of the electrons causing the auroral emissions. Furthermore, I will describe some of the short-timescale dynamics of the polar-most emissions, including their quasi-periodic nature. Finally, I will conclude with a short description of the expected outcome of the Juno mission, which will provide its first scientific results in fall 2016. [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 detailA short dive into the complexity of Jupiter’s aurorae - invited
Bonfond, Bertrand ULg

Conference (2015, April 13)

Aurorae are the atmospheric signatures of energetic processes taking place far in the magnetosphere. One of the most important results brought by high resolution imaging of the UV aurorae at Jupiter is ... [more ▼]

Aurorae are the atmospheric signatures of energetic processes taking place far in the magnetosphere. One of the most important results brought by high resolution imaging of the UV aurorae at Jupiter is the realization that there isn’t such a thing as «the aurora» at Jupiter; as these light emissions appear to arise from a variety of processes. Some are related to the interaction of the magnetospheric plasma with the moons (the satellite footprints). Others are linked with the radial motion of flux tubes through centrifugal instabilities (the injection auroral signatures). Some diffuse emissions are connected with wave-particle interaction (the equatorward diffuse emissions). Another feature is associated with the magnetosphere-ionosphere coupling (the main emission/oval). Some auroral spots are related to internally driven reconnection (the polar dawn spots). Finally, the polar-most emissions remain to be understood and this list is still incomplete. In order to illustrate the discrepancies between these various features, I will show a set of recent results derived from the analysis of Hubble Space Telescope observations. For example, I will compare the vertical profile of satellite footprints and the main emissions, and show that the energy population of the precipitating particles varies from feature to feature. Moreover, even within a single feature, spatial variations do exist. As an example, I will characterize the dawn-dusk brightness discrepancy of the main emissions and discuss its implication regarding the magnetospheric currents. And finally, the dynamics of the features also helps differentiating one type of aurora from another. This will be shown through the description of the morphological evolution of the transient flares in the polar region. [less ▲]

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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 detailTransient internally driven aurora at Jupiter discovered by Hisaki and the Hubble Space Telescope
Kimura, Tomoki; Badman, Sarah; Tao, Chihiro et al

in Geophysical Research Letters (2015), 42

Jupiter’s auroral emissions reveal energy transport and dissipation through the planet’s giant magnetosphere. While the main auroral emission is internally driven by planetary rotation in the steady state ... [more ▼]

Jupiter’s auroral emissions reveal energy transport and dissipation through the planet’s giant magnetosphere. While the main auroral emission is internally driven by planetary rotation in the steady state, transient brightenings are generally thought to be triggered by compression by the external solar wind. Here we present evidence provided by the new Hisaki spacecraft and the Hubble Space Telescope that shows that such brightening of Jupiter’s aurora can in fact be internally driven. The brightening has an excess power up to ~550 GW. Intense emission appears from the polar cap region down to latitudes around Io’s footprint aurora, suggesting a rapid energy input into the polar region by the internal plasma circulation process. [less ▲]

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See detailIn-situ & remote sensing studies of outer planet aurora
Badman, S.V.; Baines, K.H.; Bonfond, Bertrand ULg et al

Conference (2015)

The combination of in situ and remote sensing measurements of auroral processes has yielded a wealth of information about solar wind-magnetosphere-ionosphere coupling at the giant planets. Results from ... [more ▼]

The combination of in situ and remote sensing measurements of auroral processes has yielded a wealth of information about solar wind-magnetosphere-ionosphere coupling at the giant planets. Results from the 2014 joint HST-Cassini Saturn auroral campaign are highlighted to demonstrate some of the interesting features observed in situ and their auroral counterparts, including: (1) perturbations on tens of minutes timescales in the high latitude ion fluxes, magnetic field, broadband plasma waves, and auroral intensity; (2) corotating auroral intensifications and their correspondence with models of the planetary period oscillations based on magnetic field perturbations; and (3) sub-corotating auroral features and their relationship to ring current enhancements observed in Energetic Neutral Atom (ENA) observations [less ▲]

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

Conference (2015)

We report Cassini/UVIS observations of auroral vortices at Saturn propagating from midnight to noon via dawn. The emission in the dawn auroral sector is observed to consist of several detached features ... [more ▼]

We report Cassini/UVIS observations of auroral vortices at Saturn propagating from midnight to noon via dawn. The emission in the dawn auroral sector is observed to consist of several detached features that swirl with time. They have a diameter of 6000 km in the ionosphere, which would correspond to plasma vortices in the magnetosphere of 12 to 15 Rs. ENA enhancements are observed simultaneously. However, they do not show any clear vortices. We estimate the velocity of the UV auroral feature to decrease from 85% of rigid corotation (28o/h) in the most equatorward part of the aurora to 68% of rigid corotation (22o/h) in the poleward part and we demonstrate that such velocity gradient could result in swirling auroral features. Particle velocities derived from magnetospheric data in previous studies, confirm large variations of the corotation fraction as a function of radial distance. We suggest that the auroral vortices could be the ionospheric footprints of hot dynamic populations containing strong velocity gradients. Alternatively, we consider another scenario that could generate auroral vortices based on field line deformation from the magnetosphere to the ionosphere, like it is proposed for the Earth. In that case the auroral spiral is the result of some processes that occurred in the transition region between the centers of vortices where strong shear flows existed. Finally, a third possibility is considered, according to which the auroral vortices reported here are the direct optical signatures of the plasma vortical flows in the magnetopause related to Kelvin-Helmholtz instabilities. However, this might be less possible due to the very different spatial scales of the auroral features (12-15 Rs) and the observed plasma vortices in the magnetopause (1 Rs). [less ▲]

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See detailA multi-scale magnetotail reconnection event at Saturn and associated flows: Cassini/UVIS auroral observations
Radioti, Aikaterini ULg; Grodent, Denis ULg; Jia, X. et al

Conference (2015)

We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the ... [more ▼]

We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the midnight-dawn quadrant in an extended local time sector (~02 to 05 LT), which rotates with an average velocity of ~ 45% of rigid corotation. The auroral dawn enhancement reported here, given its observed location and brightness, is most probably due to hot tenuous plasma carried inward in fast moving flux tubes returning from a tail reconnection site to the dayside. These flux tubes could generate intense field-aligned currents that would cause aurora to brighten. However, the origin of tail reconnection (solar wind or internally driven) is uncertain. Based mainly on the flux variations, which do not demonstrate flux closure, we suggest that the most plausible scenario is that of internally driven tail reconnection which operates on closed field lines. The observations also reveal multiple intensifications within the enhanced region suggesting an x-line in the tail, which extends from 02 to 05 LT. The localised enhancements evolve in arc and spot-like small scale features, which resemble vortices mainly in the beginning of the sequence. These auroral features could be related to plasma flows enhanced from reconnection which diverge into multiple narrow channels then spread azimuthally and radially. We suggest that the evolution of tail reconnection at Saturn may be pictured by an ensemble of numerous narrow current wedges or that inward transport initiated in the reconnection region could be explained by multiple localised flow burst events. The formation of vortical-like structures could then be related to field-aligned currents, building up in vortical flows in the tail. An alternative, but less plausible, scenario could be that the small scale auroral structures are related to viscous interactions involving small-scale reconnection. [less ▲]

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See detailThe EChO science case
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in ArXiv e-prints (2015), 1502

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general ... [more ▼]

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional diversity observed as compared to the Solar System? EChO (Exoplanet Characterisation Observatory) has been designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large and diverse planet sample within its four-year mission lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300K-3000K) of F to M-type host stars. Over the next ten years, several new ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets. Placing the satellite at L2 provides a cold and stable thermal environment, as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. A 1m class telescope is sufficiently large to achieve the necessary spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16 micron) and SNR to be achieved by EChO, thanks to its high stability and dedicated design, would enable a very accurate measurement of the atmospheric composition and structure of hundreds of exoplanets. [less ▲]

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See detailVariability of Jupiter’s Main Auroral Emission in Response to Magnetospheric Hot Plasma Injections
Badman, Sarah; Bonfond, Bertrand ULg; Fujimoto, Masaki et al

Poster (2014, December 16)

We present observations of Jupiter’s FUV aurora acquired by the Hubble Space Telescope during a two-week interval in January 2014. The variability of the main auroral emission was studied using ... [more ▼]

We present observations of Jupiter’s FUV aurora acquired by the Hubble Space Telescope during a two-week interval in January 2014. The variability of the main auroral emission was studied using latitudinal profiles of intensity. The main oval intensity was found to be reduced when bright patches of diffuse emission were present at lower latitudes. These low latitude emissions are interpreted as the signatures of hot plasma injections from the outer magnetosphere, a process which has previously been related to interchange between the flux tubes from the outer magnetosphere and outward-moving flux tubes loaded with iogenic plasma. The main emission was also observed to broaden and shift in latitude, and occasionally display a double peak structure. These observations are interpreted with reference to the expected changes in auroral field-aligned currents associated with the replacement of the radially-stretched, mass-loaded flux tubes in the middle magnetosphere by more dipolar flux tubes containing rarefied hot plasma. [less ▲]

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See detailMulti-wavelength observations of Jupiter's aurora coordinated with Hisaki and other space telescopes
Kimura, Tomoki; Badman, Sarah; Tao, Chihiro et al

Conference (2014, December 15)

From January to April 2014, two observing campaigns by multi-wavelength remote sensing from X-ray to radio were performed to uncover energy transport process in Jupiter’s plasma environment using space ... [more ▼]

From January to April 2014, two observing campaigns by multi-wavelength remote sensing from X-ray to radio were performed to uncover energy transport process in Jupiter’s plasma environment using space telescopes and ground-based facilities. These campaigns were triggered by the new Hisaki spacecraft launched in September 2013, which is an extremely ultraviolet (EUV) space telescope of JAXA designed for planetary observations. In the first campaign in January, Hubble Space Telescope (HST) made imaging of far ultraviolet (FUV) aurora with a high special resolution (0.08”) through two weeks while Hisaki continuously monitored aurora and plasma torus emissions in EUV wavelength with a high temporal resolution (1 min<). We discovered new magnetospheric activities from the campaign data: e.g., internally-driven type auroral brightening associated with hot plasma injection, and plasma and electromagnetic filed modulations in the inner magnetosphere externally driven by the solar wind modulation. The second campaign in April was performed by Chandra X-ray Observatory (CXO), XMM newton, and Suzaku satellite simultaneously with Hisaki. Relativistic auroral accelerations in the polar region and hot plasma in the inner magnetosphere were captured by the X-ray space telescopes simultaneously with EUV monitoring of aurora and plasma torus. Auroral intensity in EUV indicated a clear periodicity of 45 minutes whereas the periodicity was not evident in X-ray intensity although previous observations by CXO indicated clear 40-minute periodicity in the polar cap X-ray aurora. In this presentation, we show remarkable scientific results obtained these campaigns. [less ▲]

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See detailTransient small-scale structure in the main auroral emission at Jupiter
Palmaerts, Benjamin ULg; Radioti, Aikaterini ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2014), 119

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See detailSolar Wind Interaction with the Magnetosphere of Jupiter : Impact on the Magnetopause and the Aurorae
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, November 20)

The outcome of the interaction between the solar wind and the Jovian magnetic field bears many differences compared to the Earth's case. At Earth, the solar wind is the major particle and energy source in ... [more ▼]

The outcome of the interaction between the solar wind and the Jovian magnetic field bears many differences compared to the Earth's case. At Earth, the solar wind is the major particle and energy source in the magnetosphere. At Jupiter, the tremendous volcanism on the moon Io is the main plasma source and Jupiter's rapid rotation (relative to its size) is the main energy source for the particles populating its magnetosphere. Combined with a weaker solar wind pressure and a larger Alfvén Mach number as the distance from the Sun increases, all these parameters modify the relative importance of large scale Dungey reconnection and viscous interaction at the magnetopause. In order to study these differences, here we present a statistical analysis of magnetopause waves and flux tube event on the Jovian magnetopause, based on in-situ measurement from the spacecraft that flew-by or orbited around Jupiter. Moreover, variations of the solar wind have significant impact on the Jovian magnetospheric current systems and such changes reflect on the aurora. In this presentation, we will also review the recent findings concerning the aurora at Jupiter and their relationship with the solar wind. [less ▲]

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See detailJupiter's Polar Cap Aurora
Grodent, Denis ULg; Bonfond, Bertrand ULg

Scientific conference (2014, November 18)

The morphology of Jupiter’s ultraviolet aurora is commonly described in terms of components located inside (poleward of) or outside (equatorward of) the main oval emission. These components may also be ... [more ▼]

The morphology of Jupiter’s ultraviolet aurora is commonly described in terms of components located inside (poleward of) or outside (equatorward of) the main oval emission. These components may also be discriminated by their temporal behaviour, where the narrowest parts of the main “oval” remain relatively stable over time periods of several hours, and the satellite footprints show large variability with timescales of minutes. Inside the main emission the so-called polar aurora, presumably corresponding to the polar cap mixing open and closed magnetic field lines, is characterized by rapid motions taking the form of swirls, giving rise to the “swirl region” and by intermittent brightenings in the “active region”. Coarse analysis of these motions suggests that they are too fast to respond to an equatorial magnetospheric forcing. Instead, they appear to be related to processes taking place in or above the ionosphere where distances travelled by plasma waves match those of the subtended auroral emission. Here, we present a preliminary improved analysis of the auroral motion in the polar region based on the application of an iterative “Advection Corrected Correlation Image Velocimetry” (ACCIV) method (Asay-Davis et al., 2009). This method allows one to build velocity fields quantifying local and overall auroral motions which may then be used to constrain their origin. [less ▲]

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See detailJupiter’s polar auroral dynamics
Grodent, Denis ULg; Bonfond, Bertrand ULg

in AAS/Division for Planetary Sciences Meeting Abstracts (2014, November 01)

The morphology of Jupiter’s ultraviolet aurora is commonly described in terms of components located inside (poleward of) or outside (equatorward of) the main oval emission. These components may also be ... [more ▼]

The morphology of Jupiter’s ultraviolet aurora is commonly described in terms of components located inside (poleward of) or outside (equatorward of) the main oval emission. These components may also be discriminated by their temporal behaviour, where the narrowest parts of the main “oval” remain relatively stable over time periods of several hours, and the satellite footprints show large variability with timescales of minutes. Inside the main emission the so-called polar aurora, presumably corresponding to the polar cap mixing open and closed magnetic field lines, is characterized by rapid motions taking the form of swirls, giving rise to the “swirl region” and by intermittent brightenings in the “active region”. Coarse analysis of these motions suggests that they are too fast to respond to an equatorial magnetospheric forcing. Instead, they appear to be related to processes taking place in or above the ionosphere where distances travelled by plasma waves match those of the subtended auroral emission. Here, we present a preliminary improved analysis of the auroral motion in the polar region based on the application of an iterative “Advection Corrected Correlation Image Velocimetry” (ACCIV) method (Asay-Davis et al., 2009). This method allows one to build velocity fields quantifying local and overall auroral motions which may then be used to constrain their origin. [less ▲]

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