References of "Gérard, Jean-Claude"
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See detailSimilarity of the Jovian satellite footprints: spots multiplicity and dynamics
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, S. V. et al

in Icarus (2017), 292(2017), 208217

In the magnetospheres of Jupiter and Saturn, the intense interaction of the satellites Io, Europa, Ganymede and Enceladus with their surrounding plasma environment leaves a signature in the aurora of the ... [more ▼]

In the magnetospheres of Jupiter and Saturn, the intense interaction of the satellites Io, Europa, Ganymede and Enceladus with their surrounding plasma environment leaves a signature in the aurora of the planet. Called satellite footprints, these auroral features appear either as a single spot (Europa and Enceladus) or as multiple spots (Io and Ganymede). Moreover, they can be followed by extended trailing tails in the case of Io and Europa, while no tail has been reported for Ganymede and Enceladus, yet. Here we show that all Jovian footprints can be made of several spots. Furthermore, the footprints all experience brightness variations on timescale of 2-3 minutes. We also demonstrate that the satellite location relative to the plasma sheet is not the only driver for the footprint brightness, but that the plasma environment and the magnetic field strength also play a role. These new findings demonstrate that the Europa and Ganymede footprints are very similar to the Io footprint. As a consequence, the processes expected to take place at Io, such as the bi-directional electron acceleration by Alfvén waves or the partial reflection of these waves on plasma density gradients, can most likely be extended to the other footprints, suggesting that they are indeed universal processes. [less ▲]

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See detailThe thermal structure of the Venus atmosphere: Intercomparison of Venus Express and ground based observations of vertical temperature and density profiles✰
Limaye, Sanjay S.; Lebonnois, Sebastien; Mahieux, Arnaud et al

in Icarus (2017), 294

The Venus International Reference Atmosphere (VIRA) model contains tabulated values of temperature and number densities obtained by the experiments on the Venera entry probes, Pioneer Venus Orbiter and ... [more ▼]

The Venus International Reference Atmosphere (VIRA) model contains tabulated values of temperature and number densities obtained by the experiments on the Venera entry probes, Pioneer Venus Orbiter and multi-probe missions in the 1980s. The instruments on the recent Venus Express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the Venus atmosphere from 40 km to about 180 km altitude from April 2006 to November 2014. Many ground based experiments have provided data on the upper atmosphere (90-130 km) temperature structure since the publication of VIRA in 1985. The "Thermal Structure of the Venus Atmosphere" Team was supported by the International Space Studies Institute (ISSI), Bern, Switzerland, from 2013 to 2015 in order to combine and compare the ground-based observations and the VEx observations of the thermal structure as a first step towards generating an updated VIRA model. Results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry. The intercomparison of the ground-based and VEx results provides for the first time a consistent picture of the temperature and density structure in the 40 km-180 km altitude range. The Venus Express observations have considerably increased our knowledge of the Venus atmospheric thermal structure above ∼40 km and provided new information above 100 km. There are, however, still observational gaps in latitude and local time above certain regions. Considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present, such as a succession of warm and cool layers. Preliminary modeling studies support the existence of such layers in agreement with a global scale circulation. The intercomparison focuses on average profiles but some VEx experiments provide sufficient global coverage to identify solar thermal tidal components. The differences between the VEx temperature profiles and the VIRA below 0.1 mbar/95 km are small. There is, however, a clear discrepancy at high latitudes in the 10-30 mbar (70-80 km) range. The VEx observations will also allow the improvement of the empirical models (VTS3 by Hedin et al., 1983 and VIRA by Keating et al., 1985) above 0.03 mbar/100 km, in particular the 100-150 km region where a sufficient observational coverage was previously missing. The next steps in order to define the updated VIRA temperature structure up to 150 km altitude are (1) define the grid on which this database may be provided, (2) fill what is possible with the results of the data intercomparison, and (3) fill the observational gaps. An interpolation between the datasets may be performed by using available General Circulation Models as guidelines. An improved spatial coverage of observations is still necessary at all altitudes, in latitude-longitude and at all local solar times for a complete description of the atmospheric thermal structure, in particular on the dayside above 100 km. New in-situ observations in the atmosphere below 40 km are missing, an altitude region that cannot be accessed by occultation experiments. All these questions need to be addressed by future missions. [less ▲]

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See detailNorth and South: Simultaneous observations of both Jovian poles from Juno and the Hubble Space Telescope
Bonfond, Bertrand ULg; Gladstone, George R.; Grodent, Denis ULg et al

Poster (2017, June 15)

On its elongated orbit, Juno flies over the poles of Jupiter every 53.5 days. The few hours before and after the perijove offer unique opportunities to observe the whole polar region from close distance ... [more ▼]

On its elongated orbit, Juno flies over the poles of Jupiter every 53.5 days. The few hours before and after the perijove offer unique opportunities to observe the whole polar region from close distance. However, Juno’s instruments can only observe one hemisphere at a time. Fortunately, the Hubble Space Telescope points its 2.4 m mirror toward the opposite hemisphere during some of these time intervals, providing truly simultaneous observations of both poles. We compare observations from Juno-UVS with Far-UV imaging sequences from the Hubble’s Space Telescope Imaging Spectrograph (STIS). Juno-UVS acquires spectrally resolved images of 17 ms exposure every 30 s Juno spin in the 70-205 nm wavelength range, while STIS can acquire about 270 consecutive 10 s images per HST orbit in the 130-160 nm range, but without any spectral resolution. Despite some differences, these datasets are similar enough in terms of spectral coverage, temporal and spatial resolution to allow direct comparisons. On Jupiter, the magnetic field is highly asymmetric and displays significant localized anomalies. Furthermore, most processes leading to auroral emissions depend on the magnetic field magnitude, either in the equatorial plane, in the acceleration regions, or in the upper atmosphere. Investigating morphological and brightness discrepancies between the two hemispheres provides precious clues on the current systems flowing in the magnetosphere and on the charged particles acceleration mechanisms. [less ▲]

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See detailMorphology of the UV aurorae Jupiter during Juno’s first perijove observations
Bonfond, Bertrand ULg; Gladstone, G. R.; Grodent, Denis ULg et al

in Geophysical Research Letters (2017)

On 27 August 2016, the NASA Juno spacecraft performed its first close-up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno-ultraviolet ... [more ▼]

On 27 August 2016, the NASA Juno spacecraft performed its first close-up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno-ultraviolet spectrometer UV imaging spectrograph acquired at that time. Data were acquired during four sequences (three in the north, one in the south) from 5:00 UT to 13:00 UT. From these observations, we produced complete maps of the Jovian aurorae, including the nightside. The sequence shows the development of intense outer emission outside the main oval, first in a localized region (255 ∘ –295 ∘ System III longitude) and then all around the pole, followed by a large nightside protrusion of auroral emissions from the main emission into the polar region. Some localized features show signs of differential drift with energy, typical of plasma injections in the middle magnetosphere. Finally, the color-ratio map in the north shows a well-defined area in the polar region possibly linked to the polar cap. [less ▲]

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See detailHST observations of Jupiter's UV aurora during Juno's orbits PJ03, PJ04 and PJ05
Grodent, Denis ULg; Gladstone, G Randall; Clarke, John T. et al

Poster (2017, April)

The intense ultraviolet auroral emissions of Jupiter are currently being monitored in the frame of a large Hubble Space Telescope (HST) program meant to support the NASA Juno prime mission. The present ... [more ▼]

The intense ultraviolet auroral emissions of Jupiter are currently being monitored in the frame of a large Hubble Space Telescope (HST) program meant to support the NASA Juno prime mission. The present study addresses the three first Juno orbits (PJ03, 04 and 05) during which HST obtained parallel observations. These three campaigns basically consist of a 2-week period bracketing the time of Juno’s closest approach of Jupiter (CA). At least one HST visit is scheduled every day during the week before and the week following CA. During the ∼12-hour period centered on CA and depending on observing constraints, several HST visits are programmed in order to obtain as many simultaneous observations with Juno-UVS as possible. In addition, at least one HST visit is obtained near Juno’s apojove, when UVS is continuously monitoring Jupiter’s global auroral power, without spatial resolution, for about 12 hours. We are using the Space Telescope Imaging Spectrograph (STIS) in time-tag mode in order to provide spatially resolved movies of Jupiter’s highly dynamic aurora with timescales ranging from seconds to several days. We discuss the preliminary exploitation of the HST data and present these results in such a way as to provide a global magnetospheric context for the different Juno instruments studying Jupiter’s magnetosphere, as well as for the numerous ground based and space based observatories participating to the Juno mission. [less ▲]

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See detailMagnetic reconnection during steady magnetospheric convection and other magnetospheric modes
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Milan, Steve E. et al

in Annales Geophysicae (2017), 35

We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar ... [more ▼]

We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar measurements of the ionospheric convection from the SuperDARN (Super Dual Aurora Radar Network) facility to estimate the open magnetic flux in the Earth's magnetosphere and the reconnection rates at the dayside magnetopause and in the magnetotail during intervals of steady magnetospheric convection (SMC). We find that SMC intervals occur with relatively high open magnetic flux (average ˜ 0.745 GWb, standard deviation ˜ 0.16 GWb), which is often found to be nearly steady, when the magnetic flux opening and closure rates approximately balance around 55 kV on average, with a standard deviation of 21 kV. We find that the residence timescale of open magnetic flux, defined as the ratio between the open magnetospheric flux and the flux closure rate, is roughly 4 h during SMCs. Interestingly, this number is approximately what can be deduced from the discussion of the length of the tail published by Dungey (1965), assuming a solar wind speed of ˜ 450 km s[SUP]-1[/SUP]. We also infer an enhanced convection velocity in the tail, driving open magnetic flux to the nightside reconnection site. We compare our results with previously published studies in order to identify different magnetospheric modes. These are ordered by increasing open magnetic flux and reconnection rate as quiet conditions, SMCs, substorms (with an important overlap between these last two) and sawtooth intervals. [less ▲]

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See detailThe Martian diffuse aurora: a model of ultraviolet and visible emissions
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Shematovich, V.I. et al

in Icarus (2017), 288

A new type of Martian aurora, characterized by an extended spatial distribution, an altitude lower than the discrete aurora and electron precipitation up to 200 keV has been observed following solar ... [more ▼]

A new type of Martian aurora, characterized by an extended spatial distribution, an altitude lower than the discrete aurora and electron precipitation up to 200 keV has been observed following solar activity on several occasions from the MAVEN spacecraft. We describe the results of Monte Carlo simulations of the production of several ultraviolet and violet auroral emissions for initial electron energies extending from 0.25 to 200 keV. These include the CO2+ ultraviolet doublet (UVD) at 288.3 and 289.6 nm and the Fox–Duffendack–Barker (FDB) bands, CO Cameron and Fourth Positive bands, OI 130.4 and 297.2 nm and CI 156.1 nm and 165.7 nm multiplets. We calculate the nadir and limb production rates of several of these emissions for a unit precipitated energy flux. Our results indicate that electrons in the range 50-200 keV produce maximum CO2+ UVD emission below 75 km, in agreement with the MAVEN observations. We calculate the efficiency of photon production per unit precipitated electron power. The strongest emissions are the CO2+ FDB, UVD and CO Cameron bands and the oxygen mission at 297.2 nm. The metastable a 3Π state which radiates the Cameron bands is deactivated by collisions below about 110 km. As a consequence, we show that the Cameron band emission is expected to peak at a higher altitude than the CO2+ UVD and FDB bands. Collisional quenching also causes the intensity ratio of the CO2+ UVD to CO Cameron bands to increase below ∼100 km in the energetic diffuse aurora. [less ▲]

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See detailGlobal Simulation of UV atmospheric Emissions
Gonzalez-Galindo; Lopez-Valverde; Forget et al

Poster (2017, January 19)

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See detailThree Types of Aurora observed by MAVEN/IUVS: Implications for Mars’ upper Atmosphere Energy Budget
Connour; Schneider; Jain et al

Poster (2017, January 17)

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See detailNO Nightglow studies status
Stiepen, Arnaud ULg; Jain; Deighan et al

Conference (2017, January 16)

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See detailMARTIAN ULTRAVIOLET AURORA: RESULTS OF MODEL SIMULATIONS
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Shematovich, V.I. et al

Conference (2017, January)

We present recent modeling results based on observations performed with the UV spectrographs on board the Mars Express and MAVEN missions.Two types of aurora are discussed: the localized and transient ... [more ▼]

We present recent modeling results based on observations performed with the UV spectrographs on board the Mars Express and MAVEN missions.Two types of aurora are discussed: the localized and transient discrete aurora and the more stable diffuse aurora observed during periods of active solar periods. [less ▲]

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See detailInfrared observations of Jovian aurora from Juno's first orbits: Main oval and satellite footprints
Mura, A.; Adriani, A.; Altieri, F. et al

in Geophysical Research Letters (2017), 44(11), 5308-5316

The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAM's imager channel observations of the H3 ... [more ▼]

The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAM's imager channel observations of the H3 + infrared emission, collected around the first Juno perijove, provide excellent spatial and temporal distribution of the Jovian aurorae, and show the morphology of the main ovals, the polar regions, and the footprints of Io, Europa and Ganymede. The extended Io “tail” persists for ~3 h after the passage of the satellite flux tube. Multi-arc structures of varied spatial extent appear in both main auroral ovals. Inside the main ovals, intense, localized emissions are observed. In the southern aurora, an evident circular region of strong depletion of H3 + emissions is partially surrounded by an intense emission arc. The southern aurora is brighter than the north one in these observations. Similar, probably conjugate emission patterns are distinguishable in both polar regions. ©2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailPreliminary JIRAM results from Juno polar observations: 3. Evidence of diffuse methane presence in the Jupiter auroral regions
Moriconi, M. L.; Adriani, A.; Dinelli, B. M. et al

in Geophysical Research Letters (2017), 44(10), 4641-4648

Throughout the first orbit of the NASA Juno mission around Jupiter, the Jupiter InfraRed Auroral Mapper (JIRAM) targeted the northern and southern polar regions several times. The analyses of the acquired ... [more ▼]

Throughout the first orbit of the NASA Juno mission around Jupiter, the Jupiter InfraRed Auroral Mapper (JIRAM) targeted the northern and southern polar regions several times. The analyses of the acquired images and spectra confirmed a significant presence of methane (CH4) near both poles through its 3.3 μm emission overlapping the H3 + auroral feature at 3.31 μm. Neither acetylene (C2H2) nor ethane (C2H6) have been observed so far. The analysis method, developed for the retrieval of H3 + temperature and abundances and applied to the JIRAM-measured spectra, has enabled an estimate of the effective temperature for methane peak emission and the distribution of its spectral contribution in the polar regions. The enhanced methane inside the auroral oval regions in the two hemispheres at different longitude suggests an excitation mechanism driven by energized particle precipitation from the magnetosphere. ©2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailPreliminary JIRAM results from Juno polar observations: 1. Methodology and analysis applied to the Jovian northern polar region
Dinelli, B. M.; Fabiano, F.; Adriani, A. et al

in Geophysical Research Letters (2017), 44(10), 4625-4632

During the first orbit around Jupiter of the NASA/Juno mission, the Jovian Auroral Infrared Mapper (JIRAM) instrument observed the auroral regions with a large number of measurements. The measured spectra ... [more ▼]

During the first orbit around Jupiter of the NASA/Juno mission, the Jovian Auroral Infrared Mapper (JIRAM) instrument observed the auroral regions with a large number of measurements. The measured spectra show both the emission of the H3+ ion and of methane in the 3–4 μm spectral region. In this paper we describe the analysis method developed to retrieve temperature and column density (CD) of the H3+ ion from JIRAM spectra in the northern auroral region. The high spatial resolution of JIRAM shows an asymmetric aurora, with CD and temperature ovals not superimposed and not exactly located where models and previous observations suggested. On the main oval averaged H3+ CDs span between 1.8 × 1012 cm−2 and 2.8 × 1012 cm−2, while the retrieved temperatures show values between 800 and 950 K. JIRAM indicates a complex relationship among H3+ CDs and temperatures on the Jupiter northern aurora. ©2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailThe tails of the satellite auroral footprints at Jupiter
Bonfond, Bertrand ULg; Saur, J.; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2017), 122

The electro-magnetic interaction between Io, Europa and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint ... [more ▼]

The electro-magnetic interaction between Io, Europa and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint, takes the form of a series of spots located slightly downstream of the feet of the field lines passing through the moon under consideration. In the case of Io, these spots are also followed by an extended tail in the downstream direction relative to the plasma flow encountering the moon. A few examples of a tail for the Europa footprint have also been reported in the northern hemisphere. Here we present a simplified Alfvénic model for footprint tails and simulations of vertical brightness profiles for various electron distribution, which favour such a model over quasi-static models. We also report here additional cases of Europa footprint tails, in both hemispheres, even though such detections are rare and difficult. Furthermore, we show that the Ganymede footprint can also be followed by a similar tail. Finally, we present a case of a 320° long Io footprint tail, while other cases in similar configurations do not display such a length. [less ▲]

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See detailPreliminary JIRAM results from Juno polar observations: 2. Analysis of the Jupiter southern H3 + emissions and comparison with the north aurora
Adriani, Alberto; Mura, Alessandro; Moriconi, M. L. et al

in Geophysical Research Letters (2017), 44(10), 4633-4640

The Jupiter InfraRed Auroral Mapper (JIRAM) aboard Juno observed the Jovian South Pole aurora during the first orbit of the mission. H3 + (trihydrogen cation) and CH4 (methane) emissions have been ... [more ▼]

The Jupiter InfraRed Auroral Mapper (JIRAM) aboard Juno observed the Jovian South Pole aurora during the first orbit of the mission. H3 + (trihydrogen cation) and CH4 (methane) emissions have been identified and measured. The observations have been carried out in nadir and slant viewing both by a L-filtered imager and a 2–5 μm spectrometer. Results from the spectral analysis of the all observations taken over the South Pole by the instrument are reported. The coverage of the southern aurora during these measurements has been partial, but sufficient to determine different regions of temperature and abundance of the H3 + ion from its emission lines in the 3–4 μm wavelength range. Finally, the results from the southern aurora are also compared with those from the northern ones from the data taken during the same perijove pass and reported by Dinelli et al. (2017). ©2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailSPICAM on Mars Express: A 10 year in-depth survey of the Martian atmosphere
Montmessin, F.; Korablev, O.; Lefèvre, F. et al

in Icarus (2017), 297

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See detailNitric Oxide Nightglow and Martian Mesospheric Circulation from MAVEN/IUVS Observations and LMD-MGCM Predictions
Stiepen, Arnaud ULg; Jain; Schneider et al

in Journal of Geophysical Research. Space Physics (2017)

We report results from a study of nitric oxide nightglow over the north- ern hemisphere of Mars during winter, the southern hemisphere during fall equinox and equatorial latitudes during summer in the ... [more ▼]

We report results from a study of nitric oxide nightglow over the north- ern hemisphere of Mars during winter, the southern hemisphere during fall equinox and equatorial latitudes during summer in the northern hemisphere based on observations of the delta and gamma bands between 190 and 270 nm by the Imaging UltraViolet Spectrograph (IUVS) on the MAVEN spacecraft. The emission reveals recombination of N and O atoms dissociated on the day- side of Mars and transported to the nightside. We characterize the bright- ness (from 0.2 to 30 kR) and altitude (from 40 to 115 km) of the NO night- glow layer, as well as its topside scale height (mean of 11 km). We show the possible impact of atmospheric waves forcing longitudinal variability, asso- ciated with an increased brightness by a factor 3 in the 140 - 200 longitude region in the northern hemisphere winter and in the -102 to -48 longitude region at summer. Such impact to the NO nightglow at Mars was not seen before. Quantitative comparison with calculations of the LMD-MGCM (Lab- oratoire de M et eorologie Dynamique - Global Circulation Model) suggests that the model globally reproduces the trends of the NO nightglow emission and its seasonal variation, but also indicates large discrepancies (up to a fac- tor 50 fainter in the model) in northern winter at low to mid-latitudes. This suggests that the predicted transport is too e cient towards the night win- ter pole in the thermosphere by 20 latitude north. [less ▲]

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See detailStagnation of Saturn's auroral emission at noon
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2017)

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