References of "Gérard, Jean-Claude"
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See detailObservation of dayside subauroral proton flashes with the IMAGE-FUV imagers
Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege; Fuselier, S. A. et al

in Geophysical Research Letters (2003), 30(3),

[1] A detailed description of an intense flash of auroral emissions that occurs equatorward of the dayside auroral oval observed with the IMAGE-FUV imagers is presented. The comparison of simultaneous ... [more ▼]

[1] A detailed description of an intense flash of auroral emissions that occurs equatorward of the dayside auroral oval observed with the IMAGE-FUV imagers is presented. The comparison of simultaneous snapshots of this subauroral flash obtained with the three FUV cameras indicates that proton precipitation is dominant. This transient proton aurora is triggered by the sudden increase of a solar wind dynamic pressure pulse. It occurs on closed field lines mapping to the equatorial plane at distances as small as similar to4 RE. A second similar event is presented, and several other cases are mentioned. These shock induced transcient emissions develop with a time scale of a few minutes (typically similar to5 min), and have a relaxation time on the order of similar to10 minutes. [less ▲]

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See detailObservation of dayside subauroral proton flashes with the IMAGE-FUV imagers
Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege; Fuselier, S. A. et al

in Geophysical Research Letters (2003), 30

A detailed description of an intense flash of auroral emissions that occurs equatorward of the dayside auroral oval observed with the IMAGE-FUV imagers is presented. The comparison of simultaneous ... [more ▼]

A detailed description of an intense flash of auroral emissions that occurs equatorward of the dayside auroral oval observed with the IMAGE-FUV imagers is presented. The comparison of simultaneous snapshots of this subauroral flash obtained with the three FUV cameras indicates that proton precipitation is dominant. This transient proton aurora is triggered by the sudden increase of a solar wind dynamic pressure pulse. It occurs on closed field lines mapping to the equatorial plane at distances as small as ~4 R[SUB]E[/SUB]. A second similar event is presented, and several other cases are mentioned. These shock induced transcient emissions develop with a time scale of a few minutes (typically ~5 min), and have a relaxation time on the order of ~10 minutes. [less ▲]

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See detailA Comparison of FUV Auroral Emissions During the April 2002 Events as seen by the IMAGE/FUV and TIMED/GUVI Instruments
Gladstone, G.; Retherford, K.; Solomon, S. et al

Conference (2002, December 01)

The auroral emissions that resulted from the series of solar particle events and magnetic storms during 14-24 April 2002 provide an excellent data set for the cross-comparison of the IMAGE/FUV and TIMED ... [more ▼]

The auroral emissions that resulted from the series of solar particle events and magnetic storms during 14-24 April 2002 provide an excellent data set for the cross-comparison of the IMAGE/FUV and TIMED/GUVI auroral imagers. The IMAGE/FUV instrument comprises the SI spectral imager (121.8 nm and 135.6 nm) and the WIC imaging photometer (LBH) and observes the entire Earth from high Earth orbit. The TIMED/GUVI spectral imager (121.6 nm, 130.4 nm, 135.6 nm, LBH short, and LBH long) scans a nadir-to-limb swath from low Earth orbit. Although there is a large difference in spatial resolution, preliminary comparison of simultaneously-observed diffuse auroral emissions indicates fairly good agreement between the calibrated brightnesses determined for common spectral features. We will present a detailed simulation of one or more of the April 2002 events as seen by each imager to determine if a single description of the auroral precipitation can self-consistently account for the proton- and electron-generated FUV emissions observed from the two spacecraft. [less ▲]

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See detailDoppler Profiles of Proton Auroral Emissions Derived From High Resolution FUV Spectra
Chua, D. H.; Dymond, K. F.; Budzien, S. A. et al

Conference (2002, December 01)

In this paper we present new FUV observations of Doppler-shifted Lyman-ë± emissions from proton aurorae obtained from the High-resolution Ionospheric and Thermospheric Spectrograph (HITS) aboard the ... [more ▼]

In this paper we present new FUV observations of Doppler-shifted Lyman-ë± emissions from proton aurorae obtained from the High-resolution Ionospheric and Thermospheric Spectrograph (HITS) aboard the Advanced Research and Global Observation Satellite (ARGOS). The Doppler profiles of the Lyman-ë± auroral emissions serve as proxies for the energy spectra of precipitating protons in the ionosphere. These observations remedy two previous shortcomings in proton aurora studies. There have been few spectral measurements of Doppler-shifted H/H[SUP]+[/SUP] emission profiles with which to validate existing models of proton flux transport in the ionosphere. Even fewer are spectral measurements of this kind over large spatial scales that would extend our understanding of proton aurora to a global level. The HITS instrument observes the Doppler shifted H Lyman-ë± emissions from proton precipitation at 0.5 Ì· resolution over the width of the auroral oval traversed by the ARGOS spacecraft. The measured Doppler spectra of proton emissions are then modeled using a Monte Carlo simulation of proton flux transport. The model parameters which include the incoming proton energy, pitch angle, and energy flux distributions are adjusted until the predicted Lyman-ë± Doppler profiles match the observations. This technique allows us to quantify the evolution of proton precipitation during varying levels of auroral activity with both spectral information and large-scale spatial coverage. We present our analysis of proton auroral observations for an isolated substorm event as an example. [less ▲]

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See detailElectron and proton excitation of the FUV aurora: Simultaneous IMAGE and NOAA observations
Coumans, Valérie ULiege; Gérard, Jean-Claude ULiege; Hubert, Benoît ULiege et al

in Journal of Geophysical Research. Space Physics (2002), 107

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in different spectral channels. The Wideband Imaging Camera (WIC) is sensitive to ... [more ▼]

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in different spectral channels. The Wideband Imaging Camera (WIC) is sensitive to the N[SUB]2[/SUB] LBH emission and NI emissions produced by both electron and proton precipitations. The SI12 camera images the Lyman-alpha emission due to incident protons only. We compare WIC and SI12 observations with model predictions based on particle measurements from the TED and the MEPED detectors on board NOAA-TIROS spacecraft. Models of the interaction of auroral particles with the atmosphere are used together with the in situ proton and electron flux and characteristic energy data to calculate the auroral brightness at the magnetic footprint of the NOAA-15 and NOAA-16 orbital tracks. The MEPED experiment measures the precipitating particles with energy higher than 30 keV, so that these comparisons include all auroral energies, in contrast to previous comparisons. A satisfactory agreement in morphology and in magnitude is obtained for most satellite overflights. The observed FUV-WIC signal is well modeled if the different spatial resolution of the two sensors is considered and the in situ measurements properly smoothed. The calculated count rate includes contributions from LBH emission, the NI 149.3 nm line, and the OI 135.6 nm line excited by electrons and protons. The proton contribution in WIC can locally dominate the electrons. The comparisons indicate that protons can significantly contribute to the FUV aurora at specific times and places and cannot be systematically neglected. The results confirm the shift of the proton auroral oval equatorward of the electron oval in the dusk sector. We also show that in some regions, especially in the dusk sector, high-energy protons dominate the proton energy flux and account for a large fraction of the Lyman-alpha and other FUV emissions. [less ▲]

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See detailExcitation of the FUV Io tail on Jupiter: Characterization of the electron precipitation
Gérard, Jean-Claude ULiege; Gustin, Jacques ULiege; Grodent, Denis ULiege et al

in Journal of Geophysical Research. Space Physics (2002), 107(A11),

[1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to ... [more ▼]

[1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to January 2001 have been combined with FUV images to map the FUV color ratio along the STIS slit. Spatially resolved spectra of the aurora carried at similar to12 Angstrom resolution have been used to determine the amount of methane absorption as measured by the FUV color ratio of the Io magnetic footprint and its trailing tail. It is found that the absorption is systematically less than in the main polar aurora, indicating a higher altitude source region. The color ratio of the north tail is shown to slowly decrease downstream from the footprint. The combination of these spectral data with a two-stream model of the interaction of energetic electrons with the Jovian thermosphere indicates that the mean energy of the electrons creating the north FUV emission ranges from similar to55 keV at the Io footprint to similar to40 keV, 20 degrees downstream in the tail. In parallel, the incident electron energy flux drops by a factor similar to6 over the same angular distance. These observations are consistent with the steady state slippage picture where the subcorotating flux tube is accelerated very slowly up to corotation owing to the nonideal coupling. It is argued that small deviations from corotation can supply sufficient energy to fuel the observed auroral emissions. It is suggested that the parallel electric field accelerating electrons out of the flux tube only moderately depends on the time elapsed since the contact with Io, although the mapping between a point in the tail and Io is very uncertain in the presence of magnetic field line slippage. [less ▲]

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See detailInterplanetary magnetic field control of afternoon-sector detached proton auroral arcs
Burch, J. L.; Lewis, W. S.; Immel, T. J. et al

in Journal of Geophysical Research. Space Physics (2002), 107

Data from the Far Ultraviolet Imager (FUV) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite show that subauroral proton arcs appear in the afternoon sector during ... [more ▼]

Data from the Far Ultraviolet Imager (FUV) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite show that subauroral proton arcs appear in the afternoon sector during geomagnetically disturbed periods when the interplanetary magnetic field rotates either from south to north or from west to east and when the magnetosphere is moderately compressed. Time series of proton aurora images show that the proton emissions are generally aligned along the equatorward part of the auroral oval. However, when interplanetary magnetic field (IMF) B[SUB]z[/SUB] changes from negative to positive the auroral oval contracts toward higher latitudes while the ring current proton precipitation remains stationary, resulting in a separation of several degrees between the latitude of the new oval position and a subauroral proton arc in the afternoon sector. A similar effect occurs when IMF B[SUB]y[/SUB] rotates from negative to positive, in which case the oval in the afternoon sector retreats toward higher latitudes, again leaving a separation between the oval and the subauroral proton arc of several degrees. Comparisons with low-altitude and geosynchronous satellite data show that the subauroral proton arc is caused by the precipitation of protons with energies from several keV to 30 keV and is likely associated with the existence of a plasmaspheric ``drainage plume.'' In contrast, the proton emissions along the main oval are caused by protons with energies generally less than 10 keV. [less ▲]

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See detailTotal electron and proton energy input during auroral substorms: Remote sensing with IMAGE-FUV
Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege; Evans, D. S. et al

in Journal of Geophysical Research. Space Physics (2002), 107

The IMAGE satellite carries three FUV imagers observing N[SUB]2[/SUB] LBH, O I 1356 Å, and HI Lyman alpha emissions in the polar aurora. These simultaneous observations are used to characterize the ... [more ▼]

The IMAGE satellite carries three FUV imagers observing N[SUB]2[/SUB] LBH, O I 1356 Å, and HI Lyman alpha emissions in the polar aurora. These simultaneous observations are used to characterize the precipitating electron and proton energy fluxes. The proton energy flux is derived from the Lyman alpha measurements on the basis of efficiency curves calculated with a Monte Carlo simulation of the proton aurora. The resulting proton contribution to the N[SUB]2[/SUB] LBH and O I 1356 Å emissions is calculated and subtracted to obtain the electron contribution in the other two channels. These two quantities are used to determine the precipitating electron average energy and energy flux. The proton and electron energy fluxes are integrated over the hemisphere to obtain the rate of auroral energy dissipation (hemispheric power) carried by the protons and electrons separately. The time development of the proton and electron aurora during four winter time events is examined. Although the onsets of the proton and electron aurora coincide in time and space, the time of the peak of energy dissipation and the recovery time are often found to differ. The fractional energy flux carried by the protons is highest during quiet periods and reaches a minimum during the most active phase of the substorms. This result is in agreement with the dependence of the fractional proton hemispheric power on magnetic activity measured by NOAA 15. The hemispheric power deduced from the FUV images is compared to the NOAA-deduced values and found to be in reasonable agreement. Sources of uncertainties in the determination of the hemispheric power are discussed on the basis of several sensitivity tests. In particular, it is found that the most critical factor is the assumption made on the energy of the auroral protons if this energy is <25 keV. [less ▲]

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See detailThe HST Campaign on Jupiter's Aurora during the Cassini Flyby
Clarke, J. T.; Grodent, Denis ULiege; Waite, J. H. et al

Conference (2002, July 29)

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See detailProton aurora in the cusp
Frey, H. U.; Mende, S. B.; Immel, T. J. et al

in Journal of Geophysical Research. Space Physics (2002), 107

Frequently, the Far Ultraviolet Instrument (FUV) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft observes intense ultraviolet emission from a localized dayside region ... [more ▼]

Frequently, the Far Ultraviolet Instrument (FUV) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft observes intense ultraviolet emission from a localized dayside region poleward of the general auroral oval location. This emission is especially distinct in the Doppler-shifted emission of hydrogen atoms produced by precipitating protons. We interpret this as a direct signature of proton precipitation into the cusp after reconnection of magnetospheric lobe field lines. This cusp signature appears only when the interplanetary magnetic field (IMF) has a positive northward B[SUB]z[/SUB] component. However, the intensity of the precipitation, and hence the intensity of UV emission, is not controlled by the magnitude of B[SUB]z[/SUB] but rather by the solar wind dynamic pressure. A statistical analysis of 18 cases observed in summer and fall 2000 shows good correlation between the UV intensity and the dynamic pressure and between the location in local time and the IMF B[SUB]y[/SUB] component. A quantitative analysis of observations from all three FUV subinstruments allows for an estimate of proton and electron energy fluxes during these times. In general, these estimates agree with results from in situ measurements by spacecraft and show that during these times, protons may contribute significantly to the overall energy deposition into the cusp. [less ▲]

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See detailMap of the precipitated electron mean energy in the Jovian aurora
Grodent, Denis ULiege; Bouchoms, R.; Gérard, Jean-Claude ULiege et al

Conference (2002, June 17)

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See detailThe HST Campaign on Jupiter's Aurora during the Cassini Flyby
Clarke, J. T.; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

Conference (2002, June 17)

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See detailIMAGE and FAST observations of substorm recovery phase aurora
Mende, Stephen B; Frey, Harald U; Carlson, Charles W et al

in Geophysical Research Letters (2002), 29

Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager (SI) channel SI12, were compared to in situ data taken by FAST. The IMAGE data segment began during the expansive phase of a ... [more ▼]

Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager (SI) channel SI12, were compared to in situ data taken by FAST. The IMAGE data segment began during the expansive phase of a substorm and a double oval configuration evolved, consisting of a set of discrete poleward auroral forms and a separate more diffuse oval. The FAST data showed that a narrow (~1.5° latitude) region of downward currents separated the two ovals. The SI-12 optical observations showed a single oval of precipitating protons located on the equatorward side within the diffuse aurora. In agreement with IMAGE, the highest intensity proton flux measured by FAST was concentrated on the equatorward region although low flux protons were present throughout the entire double oval. In the lower latitude diffuse oval occasional structured auroras were embedded. These structured auroras were mostly created by inverted V type electrons but there were narrow regions in which intense beams of accelerated electrons were seen whose energy/pitch angle distribution and accompanying electric field data were consistent with Alfven wave acceleration. The poleward oval consisted of an intense inverted V precipitation event poleward of which a weak region of Alfven wave accelerated electrons was located. From the images it appears that the Alfven wave accelerated electron event in the diffuse auroral regions and the poleward features were part of short lived or rapidly moving auroral forms. [less ▲]

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See detailGlobal comparison of magnetospheric ion fluxes and auroral precipitation during a substorm
Mende, S. B.; Frey, H. U.; Immel, T. J. et al

in Geophysical Research Letters (2002), 29

Integrated fluxes from global images taken by the High Energy Neutral Atom (HENA) and the far ultraviolet (FUV) imagers on the IMAGE spacecraft were compared for a six-hour period, during which a ... [more ▼]

Integrated fluxes from global images taken by the High Energy Neutral Atom (HENA) and the far ultraviolet (FUV) imagers on the IMAGE spacecraft were compared for a six-hour period, during which a reasonably intense substorm occurred. HENA and the FUV proton auroral imager (SI-12) monitor emissions which are representative of trapped and precipitating magnetospheric proton fluxes, respectively. For several hours prior to substorm onset, measurements of the fluxes of lower energy (10-16 and 16-27 keV) magnetospheric Energetic Neutral Atoms (ENA-s) by HENA and precipitating auroral protons by FUV SI-12 show strong similarities, with the implication that, in general, proton precipitation is controlled by a steady pitch angle diffusion process. Less similarity is seen between ENA-s and the auroral electron precipitation, which is monitored with the FUV Wideband Imaging Camera. Prior to substorm onset, ENA intensity at large radial distance (L > 8) is reduced while the overall integrated ENA flux increases signifying earthward motion and accumulation of the plasma. About 20 minutes before onset, the auroral fluxes decrease while the ENA intensity continues to grow. The observations are consistent with a pre-onset increase in plasma pressure in the inner magnetosphere without an increase in precipitation showing more efficient trapping perhaps by the distorted nightside magnetosphere. At substorm onset the increase in precipitation intensity is very sudden while the more gradual intensification of the energetic ENA-s continues. At onset the electron aurora shows an increase in intensity of one order of magnitude, while the increase in precipitating proton flux is only 50%. The intensification of the precipitation is relatively short lived (~10 minutes) while the ENA substorm enhancements last about an hour. [less ▲]

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See detailPrecipitation of auroral protons in detached arcs
Immel, Thomas J; Mende, Stephen B; Frey, Harald U et al

in Geophysical Research Letters (2002), 29

Recent global-scale observations by the IMAGE-FUV instrument demonstrate the existence of regions of particle precipitation at sub-auroral latitudes on the dayside. The signature of this precipitation is ... [more ▼]

Recent global-scale observations by the IMAGE-FUV instrument demonstrate the existence of regions of particle precipitation at sub-auroral latitudes on the dayside. The signature of this precipitation is seen infrequently, but when so, it is clear in all 3 channels of the FUV instrument. A conjugate hemisphere conjunction with the FAST satellite demonstrates the presence of precipitating protons and the notable absence of precipitating electrons in these arcs. With this knowledge, one can determine the mean energy and energy flux of the precipitating protons by intercomparison of the response in the three FUV channels. Assuming that the protons have a kappa energy distribution, the mean energy is found to be ~20 keV, with a peak in total energy flux of ~1 mW/m[SUP]2[/SUP]/sec, consistent with fits to the FAST ion measurements. These phenomena are observed mainly during times of high solar wind dynamic pressure and variable interplanetary magnetic field, and are associated with earlier nightside enhancements in the brightness and latitudinal extent of the proton aurora. [less ▲]

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See detailImaging and in Situ Particle Observations of Particles Accelerated by Auroral Electric Fields
Mende, S. B.; Carlson, C. W.; Frey, H. U. et al

Conference (2002, May 01)

Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager (SI) channels SI12 and SI13, were compared to in situ data taken by FAST for several cases of substorm onsets and following ... [more ▼]

Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager (SI) channels SI12 and SI13, were compared to in situ data taken by FAST for several cases of substorm onsets and following auroral conditions. FAST spacecraft observations had shown that the high latitude auroral ionosphere has several distinct regions and two of those are associated with intense particle precipitation The upward current region contains converging electric field structures, large-scale density cavities, down-going inverted V electrons and quasi-static potential structures. Another, sometimes distinct, region is characterized by filamentary currents containing Alfvenic electric fields, field aligned counter streaming (superthermal) electrons and ion heating transverse to B with associated large ion outflow. In two of the cases presented the satellite passed through the substorm surge on its duskward flank fairly soon after substorm onset. In these cases the superthermal wave accelerated component was clearly found to be on the polar cap boundary of the surge and could be isolated from inverted V precipitation which occurred in the more equatorward parts of the auroral oval. It is suggested that the wave accelerated precipitation is the signature of intense earthward-directed, Alfvenic Poynting fluxes usually observed at altitudes of 4-6 Re near the lobe/plasma sheet interface. In one of the cases the surge was accompanied by intense ion outflow. In three of the cases presented FAST passed through the substorm aurora at midnight or the dawn side outside of the surge and the wave accelerated electrons were less clearly separated from the inverted V type precipitation and the wave accelerated, electrons were seen to be part of very short lived transient events i.e. bursts. The ions were present equatorward of the surge with no enhancement poleward of their normal auroral oval position. The region of auroral forms, associated with intense Alfven waves propagating from the magnetosphere, are most likely to be produced by rapidly moving field lines through (substorm) dynamic reconfiguration unlike inverted V type electric field structures which may be produced by steady plasma convection. The ability to image the two different types of auroras would allow to map the field lines connected to regions of dynamic field configuration. [less ▲]

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See detailFUV Global View of the Evolution of Electrons and Protons Substorms
Meurant, M.; Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege et al

Conference (2002, May 01)

The FUV instruments on board the IMAGE satellite provide global images of the N2-LBH (WIC), OI-1356 Ì· (SI13) and Doppler shifted Lyman-alpha (SI12) emissions of the north polar aurora. The 7 Re apogee of ... [more ▼]

The FUV instruments on board the IMAGE satellite provide global images of the N2-LBH (WIC), OI-1356 Ì· (SI13) and Doppler shifted Lyman-alpha (SI12) emissions of the north polar aurora. The 7 Re apogee of the IMAGE orbit allows FUV to simultaneously image the entire auroral zone during a large fraction of the orbit. We present a result of a study of the global morphology evolution during substorm development and recovery. In order to avoid any dayglow contamination, this study is restricted to winter observation. In active regions, electron fluxes and electrons mean energies are deduced assuming a Maxwellian distribution assumption. The mean energy is derived from the WIC/SI13 ratio. Proton fluxes are also determined assuming a 8 keV proton mean energy with a Kappa distribution. The temporal dependence of the electron and proton injections is studied along with their magnetic local time and magnetic latitude variations during several substorms. In particular, the temporal evolution of the magnetic latitude of the bulk proton and electron injections is presented. Our results are found to be consistent with previous studies resting on ground based observations. [less ▲]

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See detailIMAGE-FUV multispectral observation of theta auroras.
Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege; Mende, S. B. et al

Conference (2002, May 01)

The theta aurora is an auroral structure presenting a sun-aligned transpolar arc. Five different dynamic evolution of the transpolar arcs are known, some of them being symmetrical to each other, leaving ... [more ▼]

The theta aurora is an auroral structure presenting a sun-aligned transpolar arc. Five different dynamic evolution of the transpolar arcs are known, some of them being symmetrical to each other, leaving three basically different types of transpolar auroral features. The theta aurora was previously studied with in-situ particles detectors onboard polar orbiting satellites and by ultraviolet imagers. Previous imaging works focused on the electron aurora. We use the FUV imagers onboard the IMAGE spacecraft to study separately the proton and electron contributions to the transpolar arcs at the global scale. The imagers of the IMAGE-FUV experiment remotely sense the electron aurora with the WIC and SI13 imagers observing respectively the N[SUB]2[/SUB]-LBH and OI-135.6 nm emission, while the SI12 spectrographic imager measures the Doppler-shifted Lyman-ë± emission which is solely due to the auroral proton precipitation. The three different types of transpolar aurora will be analyzed using the IMAGE-FUV imagers. In particular, the relative contribution of proton and electron to the excitation of the theta aurora will be presented. [less ▲]

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See detailSpatially resolved far ultraviolet spectroscopy of the jovian aurora
Gustin, Jacques ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

in Icarus: International Journal of Solar System Studies (2002), 157(1), 91-103

Spatially resolved spectra in four 50-Angstrom FUV spectral windows were obtained across the jovian aurora with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. Nearly ... [more ▼]

Spatially resolved spectra in four 50-Angstrom FUV spectral windows were obtained across the jovian aurora with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. Nearly simultaneous ultraviolet imaging makes it possible to correlate the intensity variations along the STIS slit with those observed in the images and to characterize the global auroral context prevailing at the time of the observations. Spectra at similar to1-Angstrom resolution taken in pairs included an unabsorbed window and a spectral region affected by hydrocarbon absorption. Both sets of spectra correspond to an aurora with a main oval brightness of about 130 kilorayleighs of H-2 emission. The far ultraviolet color ratios I(1550-1620 Angstrom)/I(1230-1300 Angstrom) are 2.3 and 5.9 for the noon and morning sectors of the main oval, respectively. We use an interactive model coupling the energy degradation of incoming energetic electrons, auroral temperature and composition, and synthetic H2 spectra to fit the intensity distribution of the H2 lines. It is found that the model best fitting globally the spectra has a soft energy component in addition to a 10 erg cm(-2) s(-1) flux of 80 keV electrons. It provides an effective H2 temperature of 540 K. The relative intensity of temperature-sensitive H-2 lines indicates differences between the auroral main oval and polar cap emissions. The amount of methane absorption across the polar region is shown to vary in a way consistent with temperature. For the second spectral pair, the polar cap shows a higher attenuation by CH4, indicating a harder precipitation along high-latitude magnetic field lines. (C) 2002 Elsevier Science (USA). [less ▲]

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