Publications of Jean-Claude Gérard
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See detailMorphology of Jupiter's Polar Auroral Bright Spot Emissions via Juno-UVS Observations
Haewsantati, Kamolporn ULiege; Bonfond, Bertrand ULiege; Wannawichian, S. et al

in Journal of Geophysical Research: Space Physics (2021), 126(2), 2020028586

Since 2016, the Juno-UVS (Ultraviolet Spectrograph) instrument has been taking spectral images of Jupiter's auroras in their full extent, including the nightside, which cannot be viewed from Earth. We ... [more ▼]

Since 2016, the Juno-UVS (Ultraviolet Spectrograph) instrument has been taking spectral images of Jupiter's auroras in their full extent, including the nightside, which cannot be viewed from Earth. We present a systematic analysis of features in Jupiter's polar auroras called auroral bright spots, which were observed by Juno-UVS during the first 25 orbits of the spacecraft. An auroral bright spot is an isolated localized and transient brightening in the polar region. Bright spots were identified in 16 perijoves (PJ) out of 24, mostly in either the northern or the southern hemisphere but rarely in both during the same PJ. The emitted power of the bright spots is time variable with peak power ranging from a few tens to a hundred of gigawatts. Moreover, we found that, for some PJs, bright spots exhibit quasiperiodic behavior. The spots, within PJ4 and PJ16, each reappeared within \textless2,000 km from the previous position in System III with periods of 28 and 22 min, respectively. This period is similar to periods previously identified in X-rays and various other observations. The bright spot positions are in a specific region in the northern hemisphere in System III, but are scattered around the magnetic pole in the southern hemisphere, near the edge of the swirl region. Furthermore, the bright spots can be seen at any local time, rather than being confined to the noon sector as previously thought from Earth-based observations. This suggests that the bright spots might not be firmly connected to the noon facing magnetospheric cusp processes. [less ▲]

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See detailDetection of a Bolide in Jupiter's Atmosphere With Juno UVS
Giles, Rohini S.; Greathouse, Thomas K.; Kammer, Joshua A. et al

in Geophysical Research Letters (2021), 48(5), 2020091797

The Ultraviolet Spectrograph (UVS) instrument on the Juno mission recorded transient bright emission from a point source in Jupiter's atmosphere. The spectrum shows that the emission is consistent with a ... [more ▼]

The Ultraviolet Spectrograph (UVS) instrument on the Juno mission recorded transient bright emission from a point source in Jupiter's atmosphere. The spectrum shows that the emission is consistent with a 9600-K blackbody located 225 km above the 1-bar level and the duration of the emission was between 17 ms and 150 s. These characteristics are consistent with a bolide in Jupiter's atmosphere. Based on the energy emitted, we estimate that the impactor had a mass of 250–5,000 kg, which corresponds to a diameter of 1–4 m. By considering all observations made with Juno UVS over the first 27 perijoves of the mission, we estimate an impact flux rate of 24,000 per year for impactors with masses greater than 250–5,000 kg. [less ▲]

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See detailAre Dawn Storms Jupiter's Auroral Substorms?
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Gladstone, G. R. et al

in AGU Advances (2021), 2(1), 2020000275

Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here, we show for ... [more ▼]

Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here, we show for the first time global views of the phenomenon, from its initiation to its end and from the nightside of the aurora onto the dayside. Based on Juno's first 20 orbits, some patterns now emerge. Small short-lived spots are often seen a couple of hours before the main emission starts to brighten and evolve from a straight arc to a more irregular one in the midnight sector. As the whole feature rotates dawn-ward, the arc then separates into two arcs with a central initially void region that is progressively filled with emissions. A gap in longitude then often forms before the whole feature dims. Finally, it transforms into an equatorward-moving patch of auroral emissions associated with plasma injection signatures. Some dawn storms remain weak and never fully develop. We also found cases of successive dawn storms within a few hours. Dawn storms thus share many fundamental features with the auroral signatures of the substorms at Earth, despite the substantial differences between the dynamics of the magnetosphere at the two planets. [less ▲]

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See detailMartian Discrete Aurorae Observed with MAVEN-IUVS: Spectral Composition and Altitude Modeling
Soret, Lauriane ULiege; Gérard, Jean-Claude ULiege; Ritter, Birgit ULiege et al

Poster (2020, December 11)

Three types of aurorae have been observed in the Martian atmosphere: the discrete, the diffuse (Schneider, 2015) and the proton aurora (Deighan et al., 2018, Ritter et al., 2018). This work concentrates ... [more ▼]

Three types of aurorae have been observed in the Martian atmosphere: the discrete, the diffuse (Schneider, 2015) and the proton aurora (Deighan et al., 2018, Ritter et al., 2018). This work concentrates on discrete aurorae, which were first discovered with the ESA Mars Express SPICAM instrument (Bertaux et al., 2005). Discrete aurorae are very localized in space, time and altitude (Leblanc et al., 2008, Gérard et al., 2015, Soret et al., 2016). They are generated by the precipitation of less energetic electrons than for diffuse aurorae (hundreds of eV compared to tens of keV). Bertaux et al. (2005) showed that discrete aurorae are characterized by the presence of the CO (a3Π–X1Σ) Cameron bands between 190 and 270 nm, the CO (A1Π–X1Σ+) Fourth Positive system (CO 4P) between 135 and 170 nm, the (B2Σu+–X2Πg) doublet at 289 nm, the OI at 297.2 nm and the 130.4 nm OI triplet emissions. The discrete aurora can now be studied using observations from the MAVEN-IUVS ultraviolet spectrograph (Schneider et al., 2019). More than 10,000 orbits of the IUVS instrument acquired from 2014 to 2020 have been analyzed for this study. Auroral signatures were automatically selected in 69 different orbits. The spectral emissions intensities have been quantified and the auroral event altitudes of the tangent point have been estimated using limb profiles. We confirm that the CO Cameron bands emission layer is located between 105 and 165 km (Bertaux et al., 2005, Soret et al., 2016). We also show the ratio between the CO Cameron bands and the CO2+ UVD intensities. Finally, we use the MAVEN Solar Wind Electron Analyzer (SWEA) measurements and a Monte-Carlo model to estimate the electron energy needed to produce a discrete auroral event. These results are of a great importance to understand the production mechanisms of discrete aurorae on Mars. [less ▲]

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See detailMars Discrete Aurora: A Comprehensive Survey for Detection & Characterization by MAVEN/IUVS
Milby, Zachariah; schneider, Nicholas; jain, Sonal et al

Poster (2020, December 11)

We present the results of a comprehensive search for discrete aurora emissions on Mars from six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a localized and ... [more ▼]

We present the results of a comprehensive search for discrete aurora emissions on Mars from six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a localized and transient form of aurora apparently unique to Mars, owing to its lack of a global magnetic field. The auroral emissions originate from precipitating electrons accelerated by the reconfiguration of Mars' crustal magnetic fields as the planet rotates relative to the external magnetic field carried by the solar wind. This process is distinct from other more widespread diffuse and proton aurora also seen at Mars. Discrete aurora was discovered in regions of strong crustal magnetic fields by the SPICAM instrument on Mars Express using limb scanning [Bertaux et al., 2005]. The emission appeared in patches ~tens of km across at altitudes ~130 km. Further analysis revealed a total of 20 instances of auroral patches during 10 years of intermittent SPICAM observations [Gérard et al., 2015]. Auroral excitation was attributed to the precipitation of electrons, typically ~100 eV - 1 keV. MAVEN/IUVS obtained the first images of the phenomenon (Schneider et al. 2018). We have examined MAVEN's mission-long dataset of nightside limb scans spanning more than 10,000 orbits over nearly 6 Earth years. Events were identified by significant emission in the CO Cameron bands (190-270 nm) and were individually confirmed to be free of stray light and cosmic ray interference. More than 500 discrete aurora events were detected, increasing the number of known events by more than an order of magnitude. The figure shows a remarkable string of distinct events seen during a single 20- minute passage of Mars' crustal field region. The observed events show a strong concentration near crustal fields in the south, but also exhibit a substantial distribution spread more uniformly over the entire planet. Some events are seen at the tangent altitude expected for electron precipitation, but many appear at lower projected altitudes. We infer these are small patches of emission in front of (or behind) the limb itself, and in some cases the spacecraft was probably imbedded in the emission. [less ▲]

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See detailMars Discrete Aurora: A Comprehensive Survey for Detection & Characterization by MAVEN/IUVS
Schneider, N.; Milby, Z.; Jain, S. et al

Conference (2020, December)

We present the results of a comprehensive search for discrete aurora emissions on Mars from six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a localized and ... [more ▼]

We present the results of a comprehensive search for discrete aurora emissions on Mars from six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a localized and transient form of aurora apparently unique to Mars, owing to its lack of a global magnetic Teld. The auroral emissions originate from precipitating electrons accelerated by the reconTguration of Mars' crustal magnetic Telds as the planet rotates relative to the external magnetic Teld carried by the solar wind. This process is distinct from other more widespread diffuse and proton aurora also seen at Mars. Discrete aurora was discovered in regions of strong crustal magnetic Telds by the SPICAM instrument on Mars Express using limb scanning [Bertaux et al., 2005]. The emission appeared in patches ~tens of km across at altitudes ~130 km. Further analysis revealed a total of 20 instances of auroral patches during 10 years of intermittent SPICAM observations [Gérard et al., 2015]. Auroral excitation was attributed to the precipitation of electrons, typically ~100 eV - 1 keV. MAVEN/IUVS obtained the Trst images of the phenomenon (Schneider et al. 2018). We have examined MAVEN's mission-long dataset of nightside limb scans spanning more than 10,000 orbits over nearly 6 Earth years. Events were identiTed by signiTcant emission in the CO Cameron bands (190-270 nm) and were individually conTrmed to be free of stray light and cosmic ray interference. More than 500 discrete aurora events were detected, increasing the number of known events by more than an order of magnitude. The Tgure shows a remarkable string of distinct events seen during a single 20-minute passage of Mars' crustal Teld region. The observed events show a strong concentration near crustal Telds in the south, but also exhibit a substantial distribution spread more uniformly over the entire planet. Some events are seen at the tangent altitude expected for electron precipitation, but many appear at lower projected altitudes. We infer these are small patches of emission in front of (or behind) the limb itself, and in some cases the spacecraft was probably imbedded in the emission. See also the related abstract by Soret et al., this conference, [less ▲]

Detailed reference viewed: 27 (5 ULiège)
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See detailComparison of ICON O+ density profiles with electron density profiles provided by COSMIC-2 and ground-based ionosondes
Wautelet, Gilles ULiege; Hubert, Benoît ULiege; Gérard, Jean-Claude ULiege et al

Poster (2020, December)

In October 2019, NASA-ICON was launched to observe the low-latitude ionosphere using in-situ and remote sensing instruments, from a LEO circular orbit at about 575 km altitude. The six satellites of the ... [more ▼]

In October 2019, NASA-ICON was launched to observe the low-latitude ionosphere using in-situ and remote sensing instruments, from a LEO circular orbit at about 575 km altitude. The six satellites of the radio-occultation program COSMIC-2 were also successfully launched and currently provide up to 3000 electron density profiles on a daily basis since October 1, 2019. Besides, the network of ground-based ionosondes is constantly growing and allows retrieving very accurate measurements of the electron density profile up to the peak altitude. These three sources of scientific observation of the Earth ionosphere therefore provide a very complementary set of data. We compare O+ density profiles provided during nighttime by the ICON-FUV instrument and during daytime by the ICON-EUV instrument against electron density profiles measured by COSMIC-2 and ionosondes. Co-located and simultaneous observations are compared on statistical grounds, and the differences between the several methods are investigated. Particular attention is given to the most important variables, such as the altitude and the density of the F-peak, hmF2 and NmF2. The time interval considered in this study covers the whole ICON data availability period, which started on November 16, 2019. Manual screening and scaling of ionograms is performed to ensure reliable ionosonde data, while COSMIC-2 data are carefully selected using an automatic quality control algorithm. A particular attention has been brought to the geometry of the observation, because the line-of-sight integration of both airglow and radio-occultation measurements assimilates horizontal and vertical gradients. As a consequence, the local density profiles obtained by inversion of the ICON and COSMIC-2 observation cannot be exactly assimilated to vertical measurements, such as vertical incidence soundings from ionosondes. This slightly limits the reach of the interpretation of the comparison between data of different origin. However, using similar observing geometries, the comparison of ICON and COSMIC-2 data does nevertheless provide very reliable and valuable comparisons. [less ▲]

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See detailObservations of Jupiter’s Hydrogen Airglow by Juno’s UVS
Gómez, D.W.; Gladstone, G.R.; Greathouse, T.K. et al

Conference (2020, December)

While the primary function of the Juno spacecraft’s Ultraviolet Spectrograph (UVS) during perijove is to observe Jupiter’s auroral features, it is also capable of detecting and measuring Jupiter’s airglow ... [more ▼]

While the primary function of the Juno spacecraft’s Ultraviolet Spectrograph (UVS) during perijove is to observe Jupiter’s auroral features, it is also capable of detecting and measuring Jupiter’s airglow. The perijove location of Juno in Jupiter’s upper atmosphere allows for the UVS to detect Hydrogen Lyman-alpha and H2 emissions as a function of zenith angle. We look at the features of Jupiter’s airglow beginning early in the mission to attempt to determine trends based on a variety of criteria, including spacecraft latitude and local time information, solar zenith angle, and the location of the emissions themselves. Juno-UVS is also well suited to search for “shuttle glow” as the spacecraft moves through Jupiter’s atmosphere. “Shuttle glow” has been observed at Earth as a result of a spacecraft re-entering or orbiting at low altitude within an atmosphere. We will describe attempts to detect and characterize these photon emissions with Juno, which moves through Jupiter’s upper atmosphere at ~60 km/s. [less ▲]

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See detailTransient Luminous Events observed in Jupiter's upper atmosphere
Giles, R.; Greathouse, T.K.; Bonfond, Bertrand ULiege et al

Conference (2020, December)

The Ultraviolet Spectrograph (UVS) is a long-slit imaging spectrograph on the Juno mission, which has been in orbit around Jupiter since July 2016. UVS covers the 68-210 nm wavelength range with a ... [more ▼]

The Ultraviolet Spectrograph (UVS) is a long-slit imaging spectrograph on the Juno mission, which has been in orbit around Jupiter since July 2016. UVS covers the 68-210 nm wavelength range with a spectral resolution of 1.3-3.0 nm, and makes use of the spacecraft’s rotation to build up an ultraviolet image as the instrument slit sweeps across the planet. The primary purpose of UVS is to map Jupiter’s far-UV auroral emissions, but the instrument has also detected seven transient bright flashes, which we suggest may be Transient Luminous Events in Jupiter’s upper atmosphere. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ~1.6 ms. Their spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 250 km above the 1-bar level. As seen by UVS, the emission regions are point sources, with maximum widths of 600-1800 km. These properties are consistent with the predicted properties of Sprites or Elves in Jupiter’s atmosphere (Yair et al., 2009, doi: 10.1029/2008JE003311, Luque et al., 2014, doi: 10.1002/2014JA020457). While tropospheric lightning has been frequently observed in Jupiter’s atmosphere, including by several other instruments on the Juno mission, Transient Luminous Events have not previously been observed in a planet other than Earth. [less ▲]

Detailed reference viewed: 34 (2 ULiège)
See detailUnderstanding Martian Proton Aurora through a Coordinated Multi-Model Comparison Campaign
Hughes, A.; Chaffin, M.; Degan, J. et al

Conference (2020, December)

Detailed reference viewed: 31 (3 ULiège)
See detailAurora to Magnetodisk Mapping: Connecting UV Emissions to Events in Jupiter’s Magnetosphere
Greathouse, T.K.; Gladstone, G.R.; Vogt, M.F. et al

Conference (2020, December)

The Juno Mission carries with it an ultraviolet spectrograph, Juno UVS, meant to map out Jupiter’s auroral emissions from an unprecedented vantage point above Jupiter’s poles. With views of the aurora at ... [more ▼]

The Juno Mission carries with it an ultraviolet spectrograph, Juno UVS, meant to map out Jupiter’s auroral emissions from an unprecedented vantage point above Jupiter’s poles. With views of the aurora at all local times, Juno UVS allows for the first comprehensive compilation of the local time variations of the auroral emissions. Using the Vogt et al. (2011, JGR 116, A03220; 2015, JGR 120, 2584-2599) magnetic flux mapping approach we invert the observed auroral emission maps into maps of those emissions in magnetodisk coordinates. In this way, we are able to reconstruct the approximate (depending on the accuracy of the Vogt mapping and JRM09 magnetic field model) structure and evolution of the source regions causing the auroral emissions leading to further insight on the dynamics of the middle to outer magnetosphere. We present mission average disk projected maps, those from assorted perijoves (close flyby of Jupiter by Juno on its highly elliptical orbit of ~53 days), and discuss their temporal evolution over timescales of minutes and hours (a single perijove) to months and years (perijove to perijove). [less ▲]

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See detailSimulating the D/H ratio and atmospheric chemistry on Mars and comparing with NOMAD observations
Daerden, F.; Neary, L.; Villanueva et al

Conference (2020, November)

The NOMAD instrument suite on the ESA-Roskosmos ExoMars Trace Gas Orbiter (TGO) observes the physical and chemical composition of the Martian atmosphere with highly resolved vertical profiles and nadir ... [more ▼]

The NOMAD instrument suite on the ESA-Roskosmos ExoMars Trace Gas Orbiter (TGO) observes the physical and chemical composition of the Martian atmosphere with highly resolved vertical profiles and nadir sounding in the IR and UV-vis domains. Vertically resolved profiles of many species (water vapor, HDO, ozone, CO, CO2, oxygen airglow, … ) and of dust and clouds were obtained for more than one Martian year [1-6]. In particular, the simultaneous detection of H2O and HDO in highly resolved profiles provide a unique dataset allowing to investigate present-day fractionation of water vapor on Mars [5]. We will provide simulations with the GEM-Mars General Circulation Model (GCM) [7-9] of HDO and the fractionation of water vapor upon cloud formation. The simulations will be compared in detail with the vertical profiles of the D/H ratio obtained from NOMAD observations. During its first year of operations, NOMAD witnessed the 2018 Global Dust Storm (GDS) during its onset, peak and decline. The redistribution of water vapor to high altitudes and latitudes observed during the GDS was explained using the GEM-Mars GCM [9]. The impact of the GDS on D/H can be estimated from these simulations, and is confirmed by the data. GEM-Mars also includes atmospheric chemistry calculations [8], and we compare these to several of the new observational datasets obtained by NOMAD. As the photolysis products of water vapor are a major driver for the atmospheric chemistry on Mars, the redistribution of water vapor over the atmosphere during the GDS is expected to have considerable impact on many other species. We present some results of the simulated impact of the GDS on atmospheric chemistry and on several of the observed species. [less ▲]

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See detailJovian auroral conductance from Juno-UVS: hemispheric asymmetry?
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Bonfond, Bertrand ULiege et al

Conference (2020, October 30)

Ionospheric conductance is important in controlling the electrical coupling between the Jovian planetary magnetosphere and its ionosphere. To some extent, it regulates the characteristics of the ... [more ▼]

Ionospheric conductance is important in controlling the electrical coupling between the Jovian planetary magnetosphere and its ionosphere. To some extent, it regulates the characteristics of the ionospheric current from above and the closure of the magnetosphere-ionosphere circuit in the ionosphere (Cowley&Bunce, 2001). Multi-spectral images collected with the UltraViolet Spectrograph (UVS) (Gladstone et al., 2017) on board Juno (Bagenal et al.,2017) have been analyzed to derive the spatial distribution of the auroral precipitation reaching the atmosphere (Bonfond et al., 2017). Electron energy flux and their characteristic energy have been used as inputs to an ionospheric model providing the production and loss rates of the main ion species, H3+, hydrocarbon ions and electrons (Gérard et al., 2020). Their steady state densities are calculated and used to determine the local distribution of the Pedersen electrical conductivity and its altitude integrated value for each UVS pixel. These values are displayed as H3+ density and Pedersen conductivity maps. We find that the main contribution to the Pedersen conductance corresponds to collisions of H3+ and hydrocarbon ions with H2. Analysis of the Birkeland current intensities based on the Juno magnetometers measurements (Kotsiaros et al. 2019) indicated that the observed current intensities are statistically larger in the south. They suggested that these differences are possibly due to a higher Pedersen conductance in this hemisphere. In order to verify this hypothesis, we calculate the conductance and H3+ density maps for perijoves 1 to 15 based on Juno-UVS spectral images. We compare the spatially integrated auroral conductance values of the two hemispheres for each orbit. The objective is to identify possible hemispheric asymmetries. [less ▲]

Detailed reference viewed: 40 (7 ULiège)
See detailA PRELIMINARY STUDY OF MIT COUPLING AT JUPITER BASED ON JUNO OBSERVATIONS AND MODELLING TOOLS
Blanc, Michel; Wang, Y.; André, Nicolas et al

Conference (2020, October 06)

The dynamics of the Jovian magnetosphere is controlled by the complex in- terplay of the planet’s fast rotation, its solar-wind interaction and its main plasma source at the Io torus. Juno observations ... [more ▼]

The dynamics of the Jovian magnetosphere is controlled by the complex in- terplay of the planet’s fast rotation, its solar-wind interaction and its main plasma source at the Io torus. Juno observations have amply demonstrated that the Magnetosphere-Ionosphere-Thermosphere (MIT) coupling process- es and regimes which control this interplay are significantly different from their Earth and Saturn counterparts. At the ionospheric level, these MIT cou- pling processes can be characterized by a set of key parameters which in- clude ionospheric electrodynamic parameters (conductances, currents and electric fields), exchanges of particles along field lines and auroral emissions. Knowledge of these key parameters in turn makes it possible to estimate the net deposition/extraction of momentum and energy into/out of the Jovian upper atmosphere. We will present a method combining Juno multi-instru- ment data (MAG, JADE, JEDI, UVS, JIRAM and WAVES), adequate modelling tools (the TRANSPLANET ionospheric dynamics model and a simplified set of ionospheric current closure equations) and the AMDA data handling tools to provide preliminary estimates of these key parameters and their variation along the ionospheric footprint of Juno’s magnetic field line and across the auroral ovals for three of the first perijoves of the mission. We will discuss how this synergistic use of data and models can also contribute to provide a better determination of poorly known parameters such as the vertical struc- ture of the auroral and polar Jovian neutral atmosphere. [less ▲]

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See detailCharacteristics of the Martian discrete auroral emissions observed with MAVEN-IUVS
Soret, Lauriane ULiege; Gérard, Jean-Claude ULiege; Schneider, N. et al

Conference (2020, October 02)

Three types of aurorae have been observed in the Martian atmosphere: the discrete, the diffuse (Schneider, 2015) and the proton aurora (Deighan et al., 2018, Ritter et al., 2018). This work concentrates ... [more ▼]

Three types of aurorae have been observed in the Martian atmosphere: the discrete, the diffuse (Schneider, 2015) and the proton aurora (Deighan et al., 2018, Ritter et al., 2018). This work concentrates on discrete aurorae, which were first discovered with the ESA Mars Express SPICAM instrument (Bertaux et al., 2005). Discrete aurorae are very localized in space, time and altitude (Leblanc et al., 2008, Gérard et al., 2015, Soret et al., 2016). They are generated by the precipitation of less energetic electrons than for diffuse aurorae (hundreds of eV compared to tens of keV). Bertaux et al. (2005) showed that discrete aurorae are characterized by the presence of the CO (a3Π–X1Σ) Cameron bands between 190 and 270 nm, the CO (A1Π–X1Σ+) Fourth Positive system (CO 4P) between 135 and 170 nm, the (B2Σu+–X2Πg) doublet at 289 nm, the OI at 297.2 nm and the 130.4 nm OI triplet emissions (see figure 1). Figure 1: Spectral signature of a discrete auroral event observed with MAVEN IUVS. The discrete aurora can now be studied using observations from the MAVEN-IUVS ultraviolet spectrograph (Schneider et al., 2019). More than 10,000 orbits of the IUVS instrument acquired from 2014 to 2020 have been analyzed for this study. Auroral signatures were automatically selected in 69 different orbits. The spectral emissions intensities have been quantified and the auroral event altitudes of the tangent point have been estimated using limb profiles. We confirm that the CO Cameron bands emission layer is located between 105 and 165 km (Bertaux et al., 2005, Soret et al., 2016). We also show the ratio between the CO Cameron bands and the CO2+ UVD intensities. Finally, we use the MAVEN Solar Wind Electron Analyzer (SWEA) measurements and a Monte-Carlo model to estimate the electron energy needed to produce a discrete auroral event. These results are of a great importance to understand the production mechanisms of discrete aurorae on Mars. See also the related abstract by Schneider et al., this conference, which looks in more detail at the occurrences and locations of the Martian discrete aurorae. References: Bertaux J.-L. et al., 2005, Discovery of an aurora on Mars, Nature 435, 790–794, https://doi.org/10.1038/nature03603 Deighan J. et al., 2018, Discovery of a proton aurora at Mars, Nature Astronomy, vol. 2, 802-807, https://doi.org/10.1038/s41550-018-0538-5 Gérard J.-C. et al., 2015, Concurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express, J. Geophys. Res. Space Physics, 120,6749–6765, https://doi.org/10.1002/2015JA021150 Leblanc F. et al., 2008, Observations of aurorae by SPICAM ultraviolet spectrograph on board Mars Express: Simultaneous ASPERA-3 and MARSIS measurements, J. Geophys. Res., 113, A08311, http://dx.doi.org/10.1029/2008JA013033 Ritter B. et al., 2018, Observations of the proton aurora on Mars with SPICAM on board Mars Express, Geophysical Research Letters, 45, 612–619, https://doi.org/10.1002/2017GL076235 Schneider N. et al., 2015, Discovery of diffuse aurora on Mars, Science, 350, 1-5, https://doi.org/10.1126/science.aad0313 Schneider N. et al., 2019, MAVEN Remote Sensing and In Situ Observations of Discrete Aurora on Mars, AGU Fall meeting, SM42B-03, https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/506680 Soret L. et al., SPICAM observations and modeling of Mars aurorae, 2016, Icarus, 264, 398-406, https://doi.org/10.1016/j.icarus.2015.09.023 [less ▲]

Detailed reference viewed: 17 (2 ULiège)
See detailMartian visible and ultraviolet dayglow: altitude, latitudinal and seasonal variations observed with NOMAD/TGO
Gérard, Jean-Claude ULiege; Aoki, Shohei ULiege; Gkouvelis, Leonardos ULiege et al

Conference (2020, October 02)

The OI 557.7 nm green line has been measured in the Martian dayglow for the first time with the UVIS visible-ultraviolet spectrograph on board ESA’s Trace Gas Orbiter (Gérard et al., 2020). The first ... [more ▼]

The OI 557.7 nm green line has been measured in the Martian dayglow for the first time with the UVIS visible-ultraviolet spectrograph on board ESA’s Trace Gas Orbiter (Gérard et al., 2020). The first observations started in April 2019 in a special mode where the spacecraft is tilted to observe the limb with the UVIS nadir channel (Vandaele et al., 2015, Patel et al., 2017). The instrument detected the presence of bright green dayglow emission on every of those observations. The main peak altitude is located near 80 km, and its intensity varies as a result of the changing distance from sun, the local time and latitude of the observations. A second, less pronounced, emission peak is observed near 110 km. Photochemical model simulations (Gkouvelis et al., 2018) used the MCD density distribution (Forget et al., 1999) have been made to understand the sources of this airglow emission. It is able to reproduce the altitude and the brightness of the airglow layer. It indicates that the green line dayglow on Mars is essentially produced by photodissociation of CO2 molecules by solar far ultraviolet radiation (Fox & Dalgarno, 1979). A fraction of the oxygen atoms is formed in the 1S metastable state that produces the green emission. In this presentation, we describe additional dayside observations obtained since December 2019. For this purpose, the spacecraft has been used in a special mode where it is re-oriented so that the UVIS channel observed the sunlit limb (Lopez-Valverde et al., 2018). We analyse the observed limb profile variations and the changing altitude of the peak emission resulting from the variations of the pressure levels in the mesosphere (Gkouvelis et al., 2020). The measured intensities are compared with model calculations of the O(1S) density in the conditions of the observations. The ratio of ultraviolet spectral features relative to the oxygen emission also observed with UVIS will also be analysed. [less ▲]

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See detailA preliminary study of Magnetosphere-Ionosphere-Thermosphere coupling key parameters at Jupiter Based on Juno multi-instrument data and modelling tools
Blanc, M.; Wang, Y.; André, N. et al

Conference (2020, September 30)

Ionospheric conductance is important in controlling the electrical coupling between the Jovian planetary magnetosphere and its ionosphere. To some extent, it regulates the characteristics of the ... [more ▼]

Ionospheric conductance is important in controlling the electrical coupling between the Jovian planetary magnetosphere and its ionosphere. To some extent, it regulates the characteristics of the ionospheric current from above and the closure of the magnetosphere-ionosphere circuit in the ionosphere (Cowley&Bunce, 2001). Multi-spectral images collected with the UltraViolet Spectrograph (UVS) (Gladstone et al., 2017) on board Juno (Bagenal et al.,2017) have been analyzed to derive the spatial distribution of the auroral precipitation reaching the atmosphere (Bonfond et al., 2017). Electron energy flux and their characteristic energy have been used as inputs to an ionospheric model providing the production and loss rates of the main ion species, H3+, hydrocarbon ions and electrons (Gérard et al., 2020). Their steady state densities are calculated and used to determine the local distribution of the Pedersen electrical conductivity and its altitude integrated value for each UVS pixel. These values are displayed as H3+ density and Pedersen conductivity maps. We find that the main contribution to the Pedersen conductance corresponds to collisions of H3+ and hydrocarbon ions with H2. Analysis of the Birkeland current intensities based on the Juno magnetometers measurements (Kotsiaros et al. 2019) indicated that the observed current intensities are statistically larger in the south. They suggested that these differences are possibly due to a higher Pedersen conductance in this hemisphere. In order to verify this hypothesis, we calculate the conductance and H3+ density maps for perijoves 1 to 15 based on Juno-UVS spectral images. We compare the spatially integrated auroral conductance values of the two hemispheres for each orbit. The objective is to identify possible hemispheric asymmetries. [less ▲]

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See detailJupiter's aurora liveliness during solar minimum
Palmaerts, Benjamin ULiege; Grodent, Denis ULiege; Bonfond, Bertrand ULiege et al

Conference (2020, September)

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See detailBright spot auroras in Jupiter’s polar region: Juno-UVS observations
Haewsantati, Kamolporn ULiege; Bonfond, Bertrand ULiege; Wannawichian, Suwicha et al

Conference (2020, September)

In July of 2016, NASA began a new era in Jupiter exploration by placing the Juno spacecraft and its highly capable suite of scientific instrumentation in a polar orbit about Jupiter. It was a unique ... [more ▼]

In July of 2016, NASA began a new era in Jupiter exploration by placing the Juno spacecraft and its highly capable suite of scientific instrumentation in a polar orbit about Jupiter. It was a unique opportunity to study Jupiter’s auroras in great details with the Ultraviolet Spectrograph (UVS) instrument during the first 25 perijoves. Here we present a systematic analysis of a newly identified feature of the polar emissions called the auroral bright spot. The bright spots have power ranging from tens to a hundred gigawatts. In a given perijove, bright spot reoccurs at almost the same system III (SIII) position within a time interval of a few to tens of minutes. Furthermore, we found a brightness quasiperiodicity of 22-28 minutes in the southern bright spots observed during perijove 4 and perijove 16. The northern bright spots locate in a confined region, near 175° SIII longitude and 65 degrees latitude, while the southern spots scatter randomly around the pole. The bright spots’ positions reported here are usually located on the edge of the swirl region (the polar-most region of Jupiter’s auroras). This feature is observed at all magnetic local times rather than being confined to the noon sector. Therefore, the bright spot is incompatible with the auroral signature of Earth-like Sun-facing cusp, as proposed in earlier works. However, due to Jupiter's rapid rotation with respect to the size of the magnetosphere, the topology of the cusp region at Jupiter is expected to be considerably complicated by the twisting of the field lines. Hence, we cannot conclude whether the bright spot is related to the Jovian cusp processes yet. Finally, we also have identified time intervals during which Juno flew through the field lines connected to the bright spot allowing further investigations of the associated particles and responsible processes. [less ▲]

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See detailSpatial Distribution of the Pedersen Conductance in the Jovian Aurora From Juno‐UVS Spectral Images
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Bonfond, Bertrand ULiege et al

in Journal of Geophysical Research. Space Physics (2020), 125

Ionospheric conductivity perpendicular to the magnetic field plays a crucial role in the electrical coupling between planetary magnetospheres and ionospheres. At Jupiter, it controls the flow of ... [more ▼]

Ionospheric conductivity perpendicular to the magnetic field plays a crucial role in the electrical coupling between planetary magnetospheres and ionospheres. At Jupiter, it controls the flow of ionospheric current from above and the closure of the magnetosphere‐ionosphere circuit in the ionosphere. We use multispectral images collected with the Ultraviolet Spectral (UVS) imager on board Juno to estimate the two‐dimensional distribution of the electron energy flux and characteristic energy. These values are fed to an ionospheric model describing the generation and loss of different ion species, to calculate the auroral Pedersen conductivity. The vertical distributions of H3+, hydrocarbon ions, and electrons are calculated at steady state for each UVS pixel to characterize the spatial distribution of electrical conductance in the auroral region. We find that the main contribution to the Pedersen conductance stems from collisions of H3+and heavier ions with H2. However, hydrocarbon ions contribute as much as 50% to Σp when the auroral electrons penetrate below the homopause. The largest values are usually associated with the bright main emission, the Io auroral footprint and occasional bright emissions at high latitude. We present examples of maps for both hemispheres based on Juno‐UVS images, with Pedersen conductance ranging from less than 0.1 to a few mhos. [less ▲]

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