References of "Grodent, Denis"
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See detailJupiter's equatorward auroral features: possible signatures of magnetospheric injections
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

in Journal of Geophysical Research - Space Physics. (in press)

The present study investigates the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in Hubble Space Telescope images of the northern and southern Jovian ... [more ▼]

The present study investigates the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in Hubble Space Telescope images of the northern and southern Jovian hemispheres obtained in 2000-2007. On average, one feature is observed every day, but several auroral structures are occasionally seen over a wide range of local times in the same image. Several properties of these features are analyzed, such as their location, emitted power and lifetime. Additionally, we magnetically map the auroral features to the equatorial plane using the VIPAL model in order to compare their observed properties with those of magnetospheric injections detected by the Galileo spacecraft. The equatorward auroral features show up between the Io footpath and the main auroral emission, at all System III longitudes, in agreement with Galileo measurements. Moreover, we compare the magnetic flux associated with these features with estimates of the out-going flux related to the radial transport of plasma in the Jovian magnetosphere and we find that they could account for at least one third of this flux. This comparative study shows that the auroral features under study are most probably related to magnetospheric injections and thus sheds light on the processes involved in the magnetosphere-ionosphere dynamics. [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 (in press)

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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 detailResponse of Microchannel Plate (MCP) Detectors to MeV Electrons: Beamline tests in support of Juno, JUICE, and Europa Mission UVS instrument investigations
Retherford, Kurt D.; Davis, Michael W.; Greathouse, Thomas K. et al

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

The response of Microchannel Plate (MCP) detectors to far-UV photons is excellent. MCPs provide a photon-counting capability that is especially useful for high-quality stellar and solar occultation ... [more ▼]

The response of Microchannel Plate (MCP) detectors to far-UV photons is excellent. MCPs provide a photon-counting capability that is especially useful for high-quality stellar and solar occultation measurements. However, use of MCPs within the Jovian magnetosphere for UV measurements is hampered by their ~30% detection efficiency to energetic electrons and ~1% efficiency to γ-rays. High-Z shielding stops energetic electrons, but creates numerous secondary particles; γ-rays are the most important of these for MCPs. These detected particles are a noise background to the measured far-UV photon signal, and at particularly intense times their combination can approach detector global count rates of ~500 kHz when operating at nominal HV levels. To address the challenges presented by the intense radiation environment experienced during Europa encounters we performed electron beam radiation testing of the Juno-UVS flight spare cross-delay line (XDL) MCP in June 2012 at MIT’s High Voltage Research Laboratory (HVRL), and again in Nov. 2013 adding an atomic-layer deposition (ALD) coated test-MCP, to measure the detection efficiency and pulse height distribution characteristics for energetic electrons and γ-rays. A key result from this UVS-dedicated SwRI IR&D project is a detailed characterization of our XDL’s response to both particles (electrons and γ-rays) and photons as a function of HV level. These results provide confidence that good science data quality is achievable when operating at Europa closest approach and/or in orbit. Comparisons with in-flight data obtained with New Horizons Pluto-Alice MeV electron response measurements at Jupiter (Steffl et al., JGR, 2012), LRO-LAMP electron and proton event data, and Juno-UVS Earth proton-belt flyby data, and recent bench tests with radioactive sources at Sensor Sciences increase this confidence. We present a description of the test setup, quantitative results, and several lessons learned to help inform future beamline test experiments dedicated to instrument developments for NASA's next large mission to Europa and ESA's JUICE mission to Ganymede. [less ▲]

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

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

The Cassini 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 ... [more ▼]

The Cassini 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 auroral images obtained from close range and high sub-spacecraft latitudes. We will plot the brightness of the individual 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. [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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See detailJupiter's equatorward auroral features : Possible signature of magnetospheric injections
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2014, September)

We investigate the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images obtained in 2000-2007. Several properties ... [more ▼]

We investigate the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images obtained in 2000-2007. Several properties of the auroral emissions are analyzed. The mapped radial position and System III longitude of the observed auroral features are in good agreement with those of the injections observed in the equatorial plane by Galileo. Finally, we discuss the processes causing auroral signatures of injections. This comparative study demonstrates that the structures under study are most probably related to magnetospheric injections and sheds light to the mechanism involved in the magnetosphere-ionosphere dynamics. [less ▲]

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See detailIsolating auroral FUV emission lines using compact, broadband instrumentation
Molyneux, P.M.; Bannister, N.P.; Bunce, E.J. et al

in Planetary and Space Science (2014), 103

Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region ... [more ▼]

Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region is low, allowing both dayside and nightside auroras to be imaged simultaneously. The ratio of intensities between certain FUV emission lines or regions can be used to characterise the precipitating particles responsible for auroral emissions, and hence is a useful diagnostic of magnetospheric dynamics. Here, we describe how the addition of simple transmission filters to a compact broadband imager design allows far ultraviolet emission ratios to be deduced while also providing large-scale instantaneous images of the aurora. The low mass and volume of such an instrument would make it well-suited for both small satellite Earth-orbiting missions and larger outer planet missions from which it could be used to characterise the tenuous atmospheres observed at several moons, as well as studying the auroral emissions of the gas giants. We present a study to investigate the accuracy of a technique to allow emission line ratio retrieval, as applied to the OI 130.4 nm and 135.6 nm emissions at Ganymede. The ratio of these emissions provides information about the atmospheric composition, specifically the relative abundances of O and O2. Using modelled FUV spectra representative of Ganymede's atmosphere, based on observations by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), we find that the accuracy of the retrieved ratios is a function of the magnitude of the ratio, with the best measurements corresponding to a ratio of ∼1.3 . [less ▲]

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See detailSpectral mapping of the FUV Jovian aurora and electron energy distribution
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2014, September)

Observations have been made with the Hubble Space Telescope in the timetag mode using the STIS long slit. During the 40 min of the observations, the slit spatially scanned the polar regions to build ... [more ▼]

Observations have been made with the Hubble Space Telescope in the timetag mode using the STIS long slit. During the 40 min of the observations, the slit spatially scanned the polar regions to build spectral maps of the jovian aurora. The emission is composed of the HI Lyman-alpha line and the H2 Lyman and Werner bands. The shorter wavelengths are partly absorbed by the methane layer overlying the bulk of the auroral emission. Since the CH4 absorption cross section drastically drops above 140 nm, the longer wavelengths are not absorbed and the intensity directly reflects the precipitated energy flux carried by the electrons. Maps of the intensity ratio of the two spectral regions will be presented, together with the associated auroral electron energy. These values will be compared with those expected from current magnetosphere-ionosphere model. They will provide input into 3-D modeling of the auroral heat source into the high-latitude Jovian upper atmosphere. [less ▲]

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See detailSaturn’s elusive nightside polar arc
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2014)

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See detailSaturn's aurorae
Stallard, Tom; Badman, Sarah; Dyudina, Ulyana et al

Scientific conference (2014, August 05)

The aurora at Saturn represents a direct manifestation of the interaction between the planet’s surrounding space environment and its upper atmosphere. Our understanding of this interaction has greatly ... [more ▼]

The aurora at Saturn represents a direct manifestation of the interaction between the planet’s surrounding space environment and its upper atmosphere. Our understanding of this interaction has greatly improved over the past decade, as a result of both in-situ and remote sensing of the aurora by Cassini, as well as through Earth-based observations. On Earth, the interaction is dominated by the connection between the magnetosphere and the Solar Wind, with opening and closing of magnetic field lines leading to sporadic aurora that are strongly controlled by changes in the solar wind. On Jupiter, internal plasma sources combine with a rotationally-dominated magnetosphere to produce intense currents associated with the breakdown in co-rotation in the magnetosphere, producing powerful and continuous aurora. Investigations into Saturn’s aurora have shown that the overall morphology changes dramatically with the arrival of compressions in the solar wind, suggesting a strong interaction with the solar wind at Earth. However, the varying rotation rate of Saturn’s magnetosphere, first identified by measurements of Saturn’s radio emission, can also be measured in many aspects of the auroral emission. This in turn suggests a degree of rotational control within the aurora. As such, the better we understanding the relative strength of these influences on the aurora of Saturn, the more we can understand how the magnetosphere interacts the planet and how, in turn, the planet drives changes in the magnetosphere. Here, we will present observations of the auroral emission directly produced by particles precipitating into Saturn’s atmosphere (radio emission), the resultant atmospheric auroral excitation this produces within of atomic hydrogen (UV and visible emission) and molecular hydrogen (UV emission), as well as thermal emission from both ions produced through auroral ionization and neutral species heated within the auroral region (IR emission). These observations show a wide variety of different auroral features ranging from the rotational pole, though the main auroral emission and down to latitudes where Saturn’s atmosphere interacts with Enceladus. Observations at these different wavelength, when compared and contrasted, reveal details about the particle precipitation process that drive them, as well as the affect these currents have on the surrounding neutral atmosphere. In-situ measurements by Cassini of the particles and magnetic field above the polar region allow us to measure and understand the field-aligned currents that produce the aurora. In comparing these currents with the auroral emission at the foot of these field lines, it is possible to understand the magnetospheric origin for Saturn’s auroral emission, as well as understanding the two-way interaction between the atmosphere and magnetosphere that is driven though the currents that produce this aurora. [less ▲]

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See detailCassini Ultraviolet Images of Saturn's Aurorae
Pryor, Wayne; Jouchoux, Alain; Esposito, Larry et al

Scientific conference (2014, August 04)

Cassini has been obtaining auroral images and spectra of Saturn with the Ultraviolet Imaging Spectrograph (UVIS). We will present highlights of the auroral images, showing a variety of morphologies ... [more ▼]

Cassini has been obtaining auroral images and spectra of Saturn with the Ultraviolet Imaging Spectrograph (UVIS). We will present highlights of the auroral images, showing a variety of morphologies, including multiple arcs, spiral forms, polar cusp activity, and rotating emission features, some of them pulsating with a roughly 1-hour period. A satellite footprint of Enceladus is occasionally visible. [less ▲]

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See detailSpace radiation parameters for EUI and the Sun Sensor of Solar Orbiter, ESIO and JUDE instruments
Rossi, Laurence ULg; Jacques, Lionel ULg; Halain, Jean-Philippe ULg et al

in Proceedings of SPIE (2014, June 18)

This paper presents predictions of space radiation parameters for four space instruments performed by the Centre Spatial de Liège (ULg – Belgium); EUI, the Extreme Ultra-violet Instrument, on-board the ... [more ▼]

This paper presents predictions of space radiation parameters for four space instruments performed by the Centre Spatial de Liège (ULg – Belgium); EUI, the Extreme Ultra-violet Instrument, on-board the Solar Orbiter platform; ESIO, Extreme-UV solar Imager for Operations, and JUDE, the Jupiter system Ultraviolet Dynamics Experiment, which was proposed for the JUICE platform. For Solar Orbiter platform, the radiation environment is defined by ESA environmental specification and the determination of the parameters is done through ray-trace analyses inside the EUI instrument. For ESIO instrument, the radiation environment of the geostationary orbit is defined through simulations of the trapped particles flux, the energetic solar protons flux and the galactic cosmic rays flux, taking the ECSS standard for space environment as a guideline. Then ray-trace analyses inside the instrument are performed to predict the particles fluxes at the level of the most radiation-sensitive elements of the instrument. For JUICE, the spacecraft trajectory is built from ephemeris files provided by ESA and the radiation environment is modeled through simulations by JOSE (Jovian Specification Environment model) then ray-trace analyses inside the instrument are performed to predict the particles fluxes at the level of the most radiation-sensitive elements of the instrument. [less ▲]

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See detailCassini nightside observations of the oscillatory motion of Saturn's northern auroral oval
Bunce, E. J.; Grodent, Denis ULg; Jinks, S. L. et al

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

recent years we have benefitted greatly from the first in-orbit multi-wavelength images of Saturn's polar atmosphere from the Cassini spacecraft. Specifically, images obtained from the Cassini UltraViolet ... [more ▼]

recent years we have benefitted greatly from the first in-orbit multi-wavelength images of Saturn's polar atmosphere from the Cassini spacecraft. Specifically, images obtained from the Cassini UltraViolet Imaging Spectrograph (UVIS) provide an excellent view of the planet's auroral emissions, which in turn give an account of the large-scale magnetosphere-ionosphere coupling and dynamics within the system. However, obtaining near-simultaneous views of the auroral regions with in situ measurements of magnetic field and plasma populations at high latitudes is more difficult to routinely achieve. Here we present an unusual case, during Revolution 99 in January 2009, where UVIS observes the entire northern UV auroral oval during a 2 h interval while Cassini traverses the magnetic flux tubes connecting to the auroral regions near 21 LT, sampling the related magnetic field, particle, and radio and plasma wave signatures. The motion of the auroral oval evident from the UVIS images requires a careful interpretation of the associated latitudinally "oscillating" magnetic field and auroral field-aligned current signatures, whereas previous interpretations have assumed a static current system. Concurrent observations of the auroral hiss (typically generated in regions of downward directed field-aligned current) support this revised interpretation of an oscillating current system. The nature of the motion of the auroral oval evident in the UVIS image sequence, and the simultaneous measured motion of the field-aligned currents (and related plasma boundary) in this interval, is shown to be related to the northern hemisphere magnetosphere oscillation phase. This is in agreement with previous observations of the auroral oval oscillatory motion. [less ▲]

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See detailDynamic auroral storms on Saturn as observed by the Hubble Space Telescope
Nichols, J. D.; Badman, S. V.; Baines, K. H. et al

in Geophysical Research Letters (2014), 41

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission ... [more ▼]

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ˜330% rigid corotation from near ˜01 h LT toward ˜08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current. [less ▲]

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See detailA Brief Review of Ultraviolet Auroral Emissions on Giant Planets
Grodent, Denis ULg

in Space Science Reviews (2014)

The morphologies of the ultraviolet auroral emissions on the giant gas planets, Jupiter and Saturn, have conveniently been described with combinations of a restricted number of basic components. Although ... [more ▼]

The morphologies of the ultraviolet auroral emissions on the giant gas planets, Jupiter and Saturn, have conveniently been described with combinations of a restricted number of basic components. Although this simplified view is very handy for a gross depiction of the giant planets’ aurorae, it fails to scrutinize the diversity and the dynamics of the actual features that are regularly observed with the available ultraviolet imagers and spectrographs. In the present review, the typical morphologies of Jupiter and Saturn’s aurorae are represented with an updated and more accurate set of components. The use of sketches, rather than images, makes it possible to compile all these components in a single view and to put aside ultraviolet imaging technical issues that are blurring the emission sources, thus preventing one from disentangling the different auroral signatures. The ionospheric and magnetospheric processes to which these auroral features allude can then be more easily accounted. In addition, the use of components of the same kind for both planets may help to put forward similarities and differences between Jupiter and Saturn. The case of the ice giants Uranus and Neptune is much less compelling since their weak auroral emissions are very poorly documented and one can only speculate about their origin. This review presents a current perspective that will inevitably evolve in the future, especially with upcoming observing campaigns and forthcoming missions like Juno. [less ▲]

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See detailQuasi-periodic flares in Jupiter's aurora : new results
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, April 29)

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode ... [more ▼]

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode of the Space Telescope Imaging Spectrograph (STIS), a high time resolution mode which allows to observe temporal variations on timescales of tens of seconds. In the present study, we focus on sudden and spectacular bursts of auroral emissions taking place in the active region located poleward of the main emissions and called “flares”. A previous study, based on only two image sequences acquired with rather unfavorable viewing angles, showed that these flares could reappear quasi-periodically on time scales of 2-3 minutes. Phenomena with similar timescales have been identified by in-situ spacecraft in relativistic electron and radio data as well as in reconnection signatures, for example. But the physical mechanism behind these ubiquitous signatures remains to be unveiled. Here we make use of the most recent and much larger data set to study in further details the occurrence rate, the period, the location, the extent and the motion of these quasi-periodic flares and to compare their behavior in both hemispheres. Quantifying these parameters allows us to narrow down the possibilities among likely explanations and provide a tentative scenario for these short timescale quasi-periodic features. [less ▲]

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See detailSaturn’s elusive transpolar arc
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, April)

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