References of "Gérard, Jean-Claude"
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See detailAuroral signatures of multiple magnetopause reconnection at Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2013)

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See detailUnraveling electron acceleration mechanisms in Ganymede's space environment through N-S conjugate imagery of Jupiter's aurora
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg et al

E-print/Working paper (2013)

There is strong scientific interest in Ganymede (Jupiter's third Galilean moon) and its surrounding environment, which stems from the likely presence of a liquid water ocean underneath its icy crust and ... [more ▼]

There is strong scientific interest in Ganymede (Jupiter's third Galilean moon) and its surrounding environment, which stems from the likely presence of a liquid water ocean underneath its icy crust and from its internally driven magnetic field. The interaction of the latter with Jupiter's magnetospheric plasma and its magnetic field gives rise to a unique situation in our solar system implying a mini-magnetosphere embedded within a giant-magnetosphere. This interaction generates Ganymede's ultraviolet auroral footprint in Jupiter's atmosphere. We propose to investigate the strong auroral connection between Jupiter and Ganymede and the variable characteristics of Ganymede's magnetosphere with an innovative approach, taking advantage of the large scale north-south asymmetries of Jupiter's magnetic field. The results obtained for Ganymede will be compared with the case of small injected hot plasma bubbles observed by the Galileo spacecraft and whose size and location are similar to those of Ganymede's magnetosphere. HST is currently the sole instrument capable of obtaining this information which pins down the proposed mechanisms linking the source and sink regions of auroral particles in the giant planets' magnetospheres. [less ▲]

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See detailVenus nitric oxide nightglow mapping from SPICAV nadir observations.
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Dumont, Maïté ULg et al

in Icarus (2013)

Nitric oxide δ (190-240 nm) and γ (255-270 nm) emissions on the Venus nightside have been observed with Venus Express SPICAV instrument operated in the nadir mode. These ultraviolet emissions arise from ... [more ▼]

Nitric oxide δ (190-240 nm) and γ (255-270 nm) emissions on the Venus nightside have been observed with Venus Express SPICAV instrument operated in the nadir mode. These ultraviolet emissions arise from the desexcitation of excited NO molecules created by radiative recombination of O(3P) and N(4S) atoms. These atoms are produced on the dayside of the planet through photodissociation of CO2 and N2 molecules and are transported to the nightside by the global subsolar to antisolar circulation. We analyze a wide dataset of nadir observations obtained since 2006 to determine the statistical distribution of the NO nightglow and its variability. Individual observations show a great deal of variability and may exhibit multiple maxima along latitudinal cuts. We compare this global map with the results obtained during the Pioneer-Venus mission and with the recent O2(a1Δg) nightglow map. The NO airglow distribution shows a statistical bright region extending from 01:00 and 03:30 local time and 25°N to 10°S, very similar to the Pioneer result obtained 35 years earlier during maximum solar activity conditions. The shift from the antisolar point and the difference with the O2 airglow indicate that superrotating zonal winds are statistically weak near 97 km, but play an important role in the lower thermosphere. We compare these results with other evidence for superrotation in the thermosphere and point out possible sources of momentum transfer. [less ▲]

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See detailAnomalous OI-989 Å intensity profile: solving an old mystery.
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Shematovich, Valery I. et al

Poster (2012, December 06)

Sounding rocket measurements conducted in 1988 under high solar activity conditions had revealed that the intensity of the thermospheric OI emission at 989 Å presents an anomalous vertical profile ... [more ▼]

Sounding rocket measurements conducted in 1988 under high solar activity conditions had revealed that the intensity of the thermospheric OI emission at 989 Å presents an anomalous vertical profile. Observation presents an intensity much higher than what can be expected compared with theoretical results including the photochemical sources of excited oxygen and the radiative transfer of the photons of the OI-989 sextuplet especially above the exobase. Attempts were conducted to clarify the discrepancy by including the non-thermal O(3P) population that appears around the exobase and higher, and that can scatter Doppler-shifted photons of the line profile farther from the rest wavelength. All attempts based on detail modeling of the photochemical processes and radiative transfer revealed unable to account for the discrepancy. Recently the FUV and EUV solar flux has been obtained at very high spectral resolution with the SOHO-SUMER instrument, revealing a significant solar oxygen emission at 989 Å, i.e. a source of photons that had never been accounted for before. In this study, we compute the radiative transfer of the OI-989 Å multiplet including the photochemical sources of excited oxygen, the scattering of incident solar photons and the effect of non-thermal atoms. We find a good agreement with the previous sounding rocket observation, solving the old mystery. We also compare the model simulations with the observations of the STP-78 satellite to better determine the relative importance of the various parameters at work in the radiative transfer of the OI-989 Å multiplet. [less ▲]

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See detailLikely Detection of UV Auroral Emission from the Magnetic Footprint of Callisto
Clarke, John; Bhattacharyya, Dolon; Montgomery, Jordan et al

Poster (2012, December 06)

A large number of UV images of Jupiter's aurora were obtained in 2007/2008 with the Hubble Space Telescope (HST) ACS/SBC camera. The initial results on variations with the solar wind conditions have been ... [more ▼]

A large number of UV images of Jupiter's aurora were obtained in 2007/2008 with the Hubble Space Telescope (HST) ACS/SBC camera. The initial results on variations with the solar wind conditions have been published elsewhere, but the large database permits other studies to be performed. In particular, while auroral emissions have been detected from the magnetic footprints of Io, Europa, and Ganymede in Jupiter's atmosphere, the footprint of Callisto has been located too close to the main auroral oval to be detected. We have thus analyzed images of the ultraviolet auroral emissions of Jupiter taken using the F115LP filter on the HST/ACS instrument. Using a unique co-addition method, we have identified a strong candidate for the footprint of Callisto on May 24, 2007. We tested this finding by applying the same co-addition method to a nearly identical auroral configuration on May 30, 2007 when Callisto was well removed in its orbit. Comparing the two co-added images, we can clearly see the presence of Callisto’s footprint on the 24th and its absence on the 30th. The method relies as well on the motion of Callisto's footprint remaining under the satellite, while most of the auroral emissions rotate with the planet. The images and analysis method will be presented in this presentation. [less ▲]

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See detailMartian thermospheric temperatures retrieved from CO2 + SPICAM dayglow measurements
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S. et al

Conference (2012, December)

A large dataset of dayside grazing limb CO2+ observations performed by the SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) instrument on board Mars Express is analyzed ... [more ▼]

A large dataset of dayside grazing limb CO2+ observations performed by the SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) instrument on board Mars Express is analyzed to retrieve Martian thermospheric temperature, as well as its variation with solar activity, season and latitude. The method permits to retrieve the temperature from the scale height of the CO2+ emission. We also present puzzling features such as limb profiles exhibiting multiple peaks and their characteristics. We furthermore study the behavior of the main emission peak of the CO2+ vertical emission profiles. The CO2+ emission at 289 nm arises from the relaxation of the CO2+* molecule in the B2Σ+ state to the X2Π state. CO2+* molecules are mainly produced in the Martian dayside through photoionisation and photoelectron impact. The CO2+ emission exhibits features that constrain the temperature and density vertical profiles of CO2. Comparisons of retrieved temperatures are made with corresponding simulations from the coupled MGCM-MTGCM. We also use a Monte-Carlo code to model the observed intensity limb profiles. [less ▲]

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See detailThe OH Venus nightglow spectrum: intensity and vibrational composition from VIRTIS-Venus Express observations
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

in Planetary and Space Science (2012), 73(1),

Limb spectra of the OH nightglow emission corresponding to the ∆v=1 and ∆v=2 sequences have been collected with the VIRTIS infrared imaging spectrograph on board Venus Express between April 2006 and ... [more ▼]

Limb spectra of the OH nightglow emission corresponding to the ∆v=1 and ∆v=2 sequences have been collected with the VIRTIS infrared imaging spectrograph on board Venus Express between April 2006 and October 2008. A detailed statistical analysis shows that the peak intensity and altitude of the two vibrational sequences are significantly correlated, with a mean intensity ratio of the two sequences of 0.38±0.37. The altitude of the maximum of the ∆v=2 emission is located ~1 km lower than ∆v=1. A spectral analysis shows that the Δv=1 sequence is composed at 44.6% by the (1–0) band, 9.3% by the (3–2) band and 7.1% by the (4–3) band. The Δv=2 emission is best fitted if solely including the (2–0) band. A non-LTE model of OH vibrational population by the O3+H reaction including radiative and collisional relaxation has been used to compare the expected spectral distribution, the altitude of the emission peak and the emission rate under different assumptions on the quenching processes to those observed with VIRTIS. The adopted carbon dioxide, atomic oxygen and ozone densities are based on recent Venus Express remote sensing measurements. We find that the “sudden death” quenching scheme by CO2 produces inadequate spectral distribution between the various bands and insufficient airglow brightness. Instead, the observed spectral distribution and the total emission intensity are reasonably well reproduced with the single quantum jump model, a O density profile peaking at 103.5 km with a maximum value of 1.9×1011 cm−3, a O3 density profile peaking at 5.8×106 cm−3 at 96.5 km and a H density profile close to 108 cm−3 between 90 and 120 km, in agreement with several photochemical models. [less ▲]

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See detailOn the origin of Saturn's polar auroral arcs
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2012, September 27)

Saturn’s main auroral emission similarly to Earth’s is suggested to be associated with the open-closed field line boundary. The polar auroral emissions at Saturn, emissions located poleward of the main ... [more ▼]

Saturn’s main auroral emission similarly to Earth’s is suggested to be associated with the open-closed field line boundary. The polar auroral emissions at Saturn, emissions located poleward of the main emission consist of several arc-like and spotty features. In this study we focus on the arc-like structures observed with the UVIS instrument onboard Cassini and we characterize them into three groups: ‘bending arcs’ arcs whose one end is connected to the main emision, ‘oval aligned arcs’ arcs oriented parallel to the main emission and ‘moving arcs’ arcs which move with time inside the main emission. We study their occurrence rate, location, size as well as their associated expansion or contraction of the main emission. Finally, we compare the auroral arcs at Saturn with those in the terrestrial aurora and we examine their relation to a combination of solar wind parameters such as northward IMF, strong IMF magnitude and high solar wind speed. [less ▲]

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See detailIsolating the 130.4 nm and 135.6 nm emissions in Ganymede’s aurora using broadband optics
Molyneux, Philippa M; Grodent, Denis ULg; Bunce, Emma J et al

Conference (2012, September 27)

We discuss a technique for isolating the two main Far Ultraviolet emission lines in Ganymede’s aurora by adding flight proven transmission filters to a broad- band, wide-field imager design. We find that ... [more ▼]

We discuss a technique for isolating the two main Far Ultraviolet emission lines in Ganymede’s aurora by adding flight proven transmission filters to a broad- band, wide-field imager design. We find that the ra- tio of OI emissions at 135.6 nm and 130.4 nm can be recovered if the transmission of the filters and other optical elements are well known. This ratio allows constraints to be placed on the relative abundances of O atoms and O2 molecules within Ganymede’s at- mosphere, leading to more accurate models of atmo- spheric composition. [less ▲]

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See detailVenus O2 night glow observations with VIRTSI/Venus Express
Migliorin, Alessandra; Piccioni, Giuseppe; Gérard, Jean-Claude ULg et al

Conference (2012, September)

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See detailSPICAM dayglow measurements: a tool to retrieve CO2 vertical density profile and exospheric temperatures
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S. et al

Conference (2012, September)

We analyze the behavior of the CO2+ and CO Cameron ultraviolet dayglow in the atmosphere of Mars through a large dataset of dayside grazing limb observations performed by the Spectroscopy for ... [more ▼]

We analyze the behavior of the CO2+ and CO Cameron ultraviolet dayglow in the atmosphere of Mars through a large dataset of dayside grazing limb observations performed by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) on board the Mars Express spacecraft. Limb profiles are studied to retrieve the temperature of the Martian exosphere and its variability with season, latitude and solar activity. We use a one-dimensional chemical-diffusive model to retrieve the main features of the emissions and constrain the temperature and density vertical profiles of the main components of the Martian atmosphere. [less ▲]

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See detailThe vertical distribution of the Venus NO nightglow: limb profiles inversion and one-dimensional modeling
Stiepen, Arnaud ULg; Soret, Lauriane ULg; Gérard, Jean-Claude ULg et al

in Icarus (2012), 220

Ultraviolet (UV) spectra of the δ (190-240 nm) and γ (225-270 nm) bands of the nitric oxide (NO) molecule have been measured on the nightside of the atmosphere of Venus with the Spectroscopy for ... [more ▼]

Ultraviolet (UV) spectra of the δ (190-240 nm) and γ (225-270 nm) bands of the nitric oxide (NO) molecule have been measured on the nightside of the atmosphere of Venus with the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument on board Venus Express (VEX). Excited NO molecules on the nightside of the planet are created by radiative recombination of O(3P) and N(4S) atoms. The atoms are produced by photodissociation of CO2 and N2 molecules on the dayside and then transported on the nightside by the global circulation. We analyze all nightside limb profiles obtained since 2006 and provide a statistical study of the nitric oxide airglow layer and its variability. We also apply a spatial deconvolution and an Abel inversion method to the limb profiles to retrieve and quantify the volume emission rate distribution and its dependence on several factors. We also show that about 10% of the limb profiles exhibits a secondary peak located above or below the main airglow peak. Furthermore, a one-dimensional chemical-diffusive model is used to simultaneously model the globally averaged NO and O2(a1Δg) airglow vertical distributions using CO2 and O density profiles rooted in VIRTIS and SPICAV observations. We find that a downward flux of 2×10 9 N(4S) atoms cm−2s−1 and a eddy diffusion coefficient equal to 1 x10 11/sqrt(n) cm−2s−1, where n is the total number density, provide the best set of values to parametrize the one-dimensional representation of the complex 3-D dynamical processes. [less ▲]

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