Publications of Bertrand Bonfond
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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 ▲]

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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 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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See detailJupiter’s polar auroral bright spots as seen by Juno-UVS
Haewsantati, Kamolporn ULiege; Bonfond, Bertrand ULiege; Wannawichian, Suwicha et al

Poster (2020, May 07)

The instruments on board the NASA Juno mission provides scientists with a wealth of unprecedented details about Jupiter. In particular, the Ultraviolet Spectrograph (UVS) is dedicated to the study of ... [more ▼]

The instruments on board the NASA Juno mission provides scientists with a wealth of unprecedented details about Jupiter. In particular, the Ultraviolet Spectrograph (UVS) is dedicated to the study of Jupiter’s aurora in the 60-200 nm wavelength range. The images taken by Juno-UVS reveals for the first time a complete view of Jupiter’s aurora, including the nightside part hidden from the Earth-orbiting Hubble Space Telescope (HST). This work aims to study Jupiter’s polar aurora using images obtained from the UVS instruments. Here we present the systematic analysis of one of the most spectacular features of Jupiter’s polar-most aurora, called the bright spot. The emitted power of the bright spots ranges from a few to a hundred GWs. Within a Juno perijove, the spots reappear at almost the same positions in system III. The time interval between two consecutive brightenings is a few tens of minutes, comparable to Jupiter’s X-ray pulsation. The comparison of the time interval with X-ray observation is under the investigation. Comparing the difference perijove sequences, the system III positions of bright spots in the northern hemisphere are concentrated in a region around 175 degrees of system III longitude and 65 degrees of latitude. On the other hand, the positions of bright spot aurora the southern hemisphere are scattered all around the pole. Previous studies suggested that the bright spot could correspond to noon facing magnetospheric cusp. However and surprisingly, we have discovered that the bright spots could map to any magnetic local time, putting this interpretation into question. [less ▲]

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See detailThe ultraviolet aurorae at Jupiter: Juno’s perspective
Bonfond, Bertrand ULiege

Scientific conference (2020, April 23)

It is always challenging to understand a complex system from fragmented pieces of information only. This is particularly true for the magnetosphere and aurorae at Jupiter, since we only had access to ... [more ▼]

It is always challenging to understand a complex system from fragmented pieces of information only. This is particularly true for the magnetosphere and aurorae at Jupiter, since we only had access to single point measurements and a few snapshots of the aurora and of the plasma torus. Furthermore, the strength of the magnetic field, the larger distance to the Sun, the presence of an internal plasma source and the rapid rotation of Jupiter make these systems fundamentally different from what we know on Earth, making the direct importation of concepts from one planet to another perilous. The Hisaki and Juno missions, together with the large Hubble Space Telescope observations campaigns supporting them, considerably helped to fill critical gaps in the datasets by giving us access to the history of events. In particular, the spatial and/or temporal continuity that characterize these new observations has allowed us to better disentangle the internal and external factors ruling the way matter and energy circulate into these systems. Moreover, high resolution images and comparisons between in-situ and remote sensing measurements also proved to be particularly powerful tools to test theories. During this seminar, I will focus on a few key results from the Juno era, including the satellite footprints, plasma injection signatures, the general auroral morphology, dawn storms and the polar emissions. I will discuss how some of them essentially confirmed our understanding of the auroral processes while others challenged them considerably. [less ▲]

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See detailJupiter
Altieri, Francesca; Adriani, Alberto; Bonfond, Bertrand ULiege et al

in Reference Module in Earth Systems and Environmental Sciences (2020)

Jupiter is the most massive and largest planet of the solar system, mainly composed of hydrogen. Its atmosphere is characterized by the presence of ammonia clouds that at mid/low latitudes are arranged in ... [more ▼]

Jupiter is the most massive and largest planet of the solar system, mainly composed of hydrogen. Its atmosphere is characterized by the presence of ammonia clouds that at mid/low latitudes are arranged in bands with alternating wind motions and storms of different size, highlighting very complex dynamics. Gradations of its distinctive ochre color are the result of the different thickness and altitude of the clouds and the presence of other minor gaseous species. Recently polar vortices systems have been discovered on both the north and south poles, with an unexpected geometry and stability. The weather layer extends much deeper into the planet than previously though. Polar regions are confirmed to be darker, with unique configurations of cyclones and several other amazing features. New results also show that the core is not homogenous, with heavy elements mixed within the hydrogen and helium envelope. Jupiter has the faintest ring system among the solar system outer planets. So far 79 satellites have been detected, the 4 largest moons (Io, Europa, Ganymede, Calisto) were observed in 1610 by Galileo Galilei and provided a clear proof that the Earth is not the center of the solar system, opening a new era in the astronomy studies. Jupiter's strong magnetic field interacts with the moons and rings, accelerating charged particles that in the polar regions of the planet give rise to intense auroral emissions. Europa, the smallest among the Galilean satellites, is one of the most exciting astrobiological targets in our solar system. [less ▲]

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See detailReconnection- and Dipolarization-Driven Auroral Dawn Storms and Injections
Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege; Clark, G. et al

in Journal of Geophysical Research: Space Physics (2020), 125(8),

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the ... [more ▼]

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the observations is a coincidence or part of an underlying physical connection. We show six clear examples from a recent Hubble Space Telescope campaign (GO-14634) that each display both auroral dawn storms and auroral injection signatures. We found that these conjugate phenomena could exist during intervals of either relatively low or high auroral activity, as evidenced by the varied levels of total auroral power. In situ observations of the magnetosphere by Juno show a strong magnetic reconnection event inside of 45 Jupiter radii (RJ) on the predawn sector, followed by two dipolarization events within the following 2 hr, coincident with the auroral dawn storm and auroral injection event. We therefore suggest that the auroral dawn storm is the manifestation of magnetic reconnection in the dawnside magnetosphere. The dipolarization region is mapped to the auroral injection, strongly suggesting that this was associated with the auroral injection. Since magnetic reconnection and dipolarization are physically connected, we therefore suggest that the often-conjugate auroral dawn storm and auroral injection events are also physically connected consequences. ©2020. The Authors. [less ▲]

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See detailA New Framework to Explain Changes in Io's Footprint Tail Electron Fluxes
Szalay, J. R.; Allegrini, F.; Bagenal, F. et al

in Geophysical Research Letters (2020), 47(18), 2020089267

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). The strength of precipitating electron fluxes is ... [more ▼]

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). The strength of precipitating electron fluxes is dominantly organized by “Io-Alfvén tail distance,” the angle along Io's orbit between Io and an Alfvén wave trajectory connected to the tail aurora. These fluxes best fit an exponential as a function of down-tail extent with an e-folding distance of 21°. The acceleration region altitude likely increases down-tail, and the majority of parallel electron acceleration sustaining the tail aurora occurs above 1 RJ in altitude. We do not find a correlation between the tail fluxes and the power of the initial Alfvén wave launched from Io. Finally, Juno has likely transited Io's Main Alfvén Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes 600 mW/m2 and an acceleration region extending as low as 0.4 RJ in altitude. [less ▲]

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See detailEnergy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission
Allegrini, Frédéric A.; Mauk, Barry H.; Clark, George B. et al

in Journal of Geophysical Research: Space Physics (2020), 125(4), 2019027693

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the ... [more ▼]

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies ( 100 eV to 1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (\textless10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of 51. A refined current sheet model will likely bring this boundary closer to the expected 20–30 RJ. Outside that region, the \textgreater100-keV electrons contribute to most (\textgreater 70–80\%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model. [less ▲]

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See detailEnergetic Particles and Acceleration Regions Over Jupiter's Polar Cap and Main Aurora: A Broad Overview
Mauk, Barry H.; Clark, George B.; Gladstone, G. Randall et al

in Journal of Geophysical Research: Space Physics (2020), 125(3), 2019027699

Previous Juno mission event studies revealed powerful electron and ion acceleration, to 100s of kiloelectron volts and higher, at low altitudes over Jupiter's main aurora and polar cap (PC; poleward of ... [more ▼]

Previous Juno mission event studies revealed powerful electron and ion acceleration, to 100s of kiloelectron volts and higher, at low altitudes over Jupiter's main aurora and polar cap (PC; poleward of the main aurora). Here we examine 30–1200 keV JEDI-instrument particle data from the first 16 Juno orbits to determine how common, persistent, repeatable, and ordered these processes are. For the PC regions, we find (1) upward electron angle beams, sometimes extending to megaelectron volt energies, are persistently present in essentially all portions of the polar cap but are generated by two distinct and spatially separable processes. (2) Particle evidence for megavolt downward electrostatic potentials are observable for 80 of the polar cap crossings and over substantial fractions of the PC area. For the main aurora, with the orbit favoring the duskside, we find that (1) three distinct zones are observed that are generally arranged from lower to higher latitudes but sometimes mixed. They are designated here as the diffuse aurora (DifA), Zone-I (ZI(D)) showing primarily downward electron acceleration, and Zone-II (ZII(B)) showing bidirectional acceleration with the upward intensities often greater than downward intensities. (2) ZI(D) and ZII(B) sometimes (but not always) contain, respectively, downward electron inverted Vs and downward proton inverted Vs, (potentials up to 400 kV) but, otherwise, have broadband distributions. (3) Surprisingly, both ZI(D) and ZII(B) can generate equally powerful auroral emissions. It is suggested but demonstrated for intense portions of only one auroral crossing, that ZI(D) and ZII(B) are associated, respectively, with upward and downward electric currents. [less ▲]

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See detailWave-particle interactions associated with Io’s auroral footprint: Evidence of Alfvén, ion cyclotron, and whistler modes
Sulaiman, A. H.; Hospodarsky, G. B.; Elliott, S. S. et al

in Geophysical Research Letters (2020), n/a(n/a), 2020088432

The electrodynamic coupling between Io and Jupiter gives rise to wave-particle interactions across multiple spatial scales. Here we report observations during Juno’s 12th perijove (PJ) high-latitude ... [more ▼]

The electrodynamic coupling between Io and Jupiter gives rise to wave-particle interactions across multiple spatial scales. Here we report observations during Juno’s 12th perijove (PJ) high-latitude northern crossing of the flux tube connected to Io’s auroral footprint. We focus on plasma wave measurements, clearly differentiating between MHD, ion, and electron scales. We find (i) evidence of Alfvén waves undergoing a turbulent cascade, suggesting Alfvénic acceleration processes together with observations of bi-directional, broadband electrons; (ii) intense ion cyclotron waves with an estimated heating rate that is consistent with the generation of ion conics reported by Clark et al. (in prep); and (iii) whistler-mode auroral hiss radiation excited by field-aligned electrons. Such high-resolution wave and particle measurements provide an insight into satellite interactions in unprecedented detail. We further anticipate that these spatially well-constrained results can be more broadly applied to better understand processes of Jupiter’s main auroral oval. [less ▲]

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See detailAlfvénic Acceleration Sustains Ganymede's Footprint Tail Aurora
Szalay, Jamey R.; Allegrini, Frederic; Bagenal, Fran et al

in Geophysical Research Letters (2020), 47(3), 2019086527

Integrating simultaneous in-situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvénic acceleration mechanisms are responsible for ... [more ▼]

Integrating simultaneous in-situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvénic acceleration mechanisms are responsible for Ganymede's auroral footprint tail. Magnetic field perturbations exhibit enhanced Alfvénic activity with Poynting fluxes of 100 mW/m2. These perturbations are capable of accelerating the observed broadband electrons with precipitating fluxes of 11 mW/m2, such that Alfvénic power is transferred to electron acceleration with 10 efficiency. The UV emissions are consistent with in-situ electron measurements, indicating 13 ± 3 mW/m2 of precipitating electron flux. Juno crosses flux tubes with both upward and downward currents connected to the auroral tail exhibiting small-scale structure. We identify an upward electron conic in the downward current region, possibly due to acceleration by inertial Alfvén waves near the Jovian ionosphere. In concert with in-situ observations at Io's footprint tail, these results suggest that Alfvénic acceleration processes are universally applicable to magnetosphere-satellite interactions. [less ▲]

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See detailProton Acceleration by Io's Alfvénic Interaction
Szalay, J. R.; Bagenal, F.; Allegrini, F. et al

in Journal of Geophysical Research: Space Physics (2020), 125(1), 2019027314

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked ... [more ▼]

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked with Io's auroral footprint tail aurora, we present new evidence for proton acceleration due to Io's Alfvénic interaction with Jupiter's magnetosphere. Separate populations were accelerated above the Io torus and at high latitudes near Jupiter. The timing suggests the acceleration is due to Alfvén waves associated with Io's Main Alfvén Wing. The inferred high-latitude proton acceleration region spans 0.92.5 Jovian radii in altitude, comparable to the expected location for electron acceleration, and suggests the associated Alfvén waves are able to accelerate electrons and protons in similar locations. The proton populations magnetically connected to Io's orbit are recently perturbed, equilibrating with the nominal torus plasma population on a timescale smaller than Io's System III orbital period of 13 h, likely due to wave-particle interactions. The tail populations are split into a wake-like structure with distinct inner and outer regions, where the inner region maps to an equatorial width nearly identical to the diameter of Io. The approximately symmetric surrounding outer regions are each slightly smaller than the central region and may be related to Io's atmospheric extent. The nominal, corotational torus proton population exhibits energization throughout all regions, peaking at the anti-Jovian flank of the inner core region mapping to Io's diameter. These proton observations suggest Alfvén waves are capable of accelerating protons in multiple locations and provide further evidence that Io's Alfvénic interaction is bifurcated. [less ▲]

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See detailComparing Electron Radiation Belts and New Lessons from Jupiter
Mauk, Barry; Becker, Heidi; Bonfond, Bertrand ULiege et al

Conference (2019, December 13)

We revisit comparisons between the electron radiation belts of all of the strongly magnetized planets of the solar system; specifically those of Earth, Jupiter, Saturn, Uranus, and Neptune. Many features ... [more ▼]

We revisit comparisons between the electron radiation belts of all of the strongly magnetized planets of the solar system; specifically those of Earth, Jupiter, Saturn, Uranus, and Neptune. Many features are worthy of reexamination in the light of new understandings achieved by such recent missions as the Van Allen Probes at Earth and Juno at Jupiter. One example is the unexpectedly intense radiation belts at the otherwise anemic magnetosphere of Uranus. At Jupiter a key mystery is how such robust high energy tails of the distributions are generated throughout the jovian radiation belt regions. One of the unexpected findings of the Juno mission is just how energetic are the auroral acceleration processes. Upward broadband acceleration commonly extends into the multi-MeV energy ranges (figure) and even > 10 MeV. We investigate here the hypothesis that such auroral acceleration plays a critical role in the seeding the generation of Jupiter’s uniquely energetic electron radiation belts. Time permitting, we also address challenges of applying lessons from planetary radiation belts to electron radiation regions outside of our solar system. [less ▲]

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See detailIn situ observation of decametric Jovian radio sources with Juno: comparison with simultaneous radio, electron and UV data
Louis, Corentin; Louarn, Philippe; Kurth, William et al

Poster (2019, December 12)

Since the discovery of the jovian auroral radio emissions, the position of the different radio source components (broadband kilometric (bKOM), hectometric (HOM) and decametric (DAM)) and their association ... [more ▼]

Since the discovery of the jovian auroral radio emissions, the position of the different radio source components (broadband kilometric (bKOM), hectometric (HOM) and decametric (DAM)) and their association with far ultraviolet (FUV) auroral emissions have been discussed extensively. We recently surveyed Juno’s first fifteen perijoves to track local radio sources from Juno/Waves in situ measurements (50 Hz–40 MHz). We conclude that the bKOM, HOM and DAM radio sources are located at different altitudes on the same magnetic field lines, with M-shell ranging from 10 to 62. Comparisons with the Jovian FUV auroral images simultaneously acquired by the Hubble Space Telescope (HST) reveals a partial spatial colocation between the FUV emission of the main oval and the radio sources studied here. These work focuses on Juno crossings of DAM sources for which FUV observations (HST/STIS, Juno/UVS), radio (Juno/Waves) and electron (Juno/JADE) measurements weer simultaneously acquired. These allow us to (i) better constrain the source locations, (ii) better understand the link between UV and DAM radio emissions, (iii) obtain the electron distribution function and the electron energy flux involved in the DAM radio emissions and (iv) compare with the theoretical radio emission process known as the Cyclotron Maser Instability. [less ▲]

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See detailAn Initial Survey of Juno-UVS Auroral Emission Spectra
Gladstone, Randy; Greathouse, Thomas; Versteeg, Maarten et al

Conference (2019, December 12)

We present an initial Juno-UVS survey of spectra of the major features of Jupiter’s ultraviolet auroras, which primarily include band emissions of H2 excited by electron impact, and the Lyman series of H ... [more ▼]

We present an initial Juno-UVS survey of spectra of the major features of Jupiter’s ultraviolet auroras, which primarily include band emissions of H2 excited by electron impact, and the Lyman series of H arising from electron impact dissociative excitation of H2. The primary difference found in most of the observed spectra is the column of hydrocarbons (mostly methane) overlying the aurora production layer in Jupiter’s atmosphere. This leads to the “color ratio” of the emissions, commonly defined as the ratio of auroral emissions at wavelengths 155-162 nm, where methane is transparent, to those at 125-130 nm, where methane is strongly absorbing. Over the course of the Juno mission, it has been found that the brightness of most auroral features known from previous observations from Earth orbit have a strong dependence on local time. The primary purpose of this survey is to examine if other details in the spectra of these features are likewise correlated with local time, and whether they are also sensitive to other changes, either in the precipitating particles (e.g., the mean electron energy) or in the auroral atmosphere (e.g., the ambient H2 vibrational distribution). [less ▲]

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See detailParticle Acceleration by Io’s Alfvénic Interaction (Invited)
Szalay, Jamey; Allegrini, Frederic; Bagenal, Fran et al

Conference (2019, December 12)

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at a range of latitudes and altitudes. The Jovian Auroral Distributions Experiment (JADE) instrument onboard Juno made ... [more ▼]

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at a range of latitudes and altitudes. The Jovian Auroral Distributions Experiment (JADE) instrument onboard Juno made observations of accelerated electrons and protons connected to the Io footprint tail aurora. JADE observed planetward electron energy fluxes of ~70 mW/m2 near the Io footprint, and ~10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased in amplitude down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel electric potential.Juno observed fine structure on scales of ~10s km, and confirmed independently with electron and wave measurements that a bifurcated tail can intermittently exist. Additionally, we report measurements that suggest proton acceleration is driven by Io’s Alfvénic interaction. While connected to Io’s footprint tail, JADE observed multiple proton populations accelerated in different magnetospheric locations, as well as a bifurcated proton tail structure. We will present these electron and proton observations and discuss how they fit into our evolving understanding of Io’s interaction with the Jovian magnetosphere. [less ▲]

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See detailMagnetosphere Mapping of Jupiter’s Polar Auroral Bright Spot
Haewsantati, Kamolporn ULiege; Wannawichian, Suwicha; Bonfond, Bertrand ULiege et al

Poster (2019, December 11)

This work presents the study of presents the study of polar bright spots, unstable and ambiguous features in Jupiter’s polar aurora. Images were taken by the Hubble Space Telescope (HST) using the ... [more ▼]

This work presents the study of presents the study of polar bright spots, unstable and ambiguous features in Jupiter’s polar aurora. Images were taken by the Hubble Space Telescope (HST) using the Advanced Camera for Surveys (ACS) instrument. We analyzed the brightness and locations of the bright spots to study their variability. Here we present eight bright spots which were clearly seen in Jupiter’s aurora images taking during May-June 2007. The latitude and longitude locations of bright spots were found to be colocated to within 10 degrees. In most cases, these features evolve from an undetermined shape into a well confined spots, before they eventually fade into the background emission. The counterpart of these bright spots in Jupiter's magnetosphere were determined using flux equivalent method proposed by Vogt et al. (2011 and 2015) and magnetic field tracing method, based on several magnetic models and direct observations. We find that the mapped locations in magnetosphere correspond to distances larger than ~70 Jovian radii from Jupiter with local time mostly near noon. The results suggest that the bright spots can be related with the polar cusp process, which remain poorly understood. [less ▲]

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See detailObservations of Auroral “Raindrops” in Jupiter’s Polar Region by Juno-UVS
Hue, Vincent; Greathouse, Thomas; Gladstone, Randy et al

Poster (2019, December 11)

Juno-UVS has observed Jupiter’s FUV auroral emissions during multiple close flybys following Juno’s orbital insertion on 5 July 2016. Each perijove provides a different snapshot of the Jovian auroral ... [more ▼]

Juno-UVS has observed Jupiter’s FUV auroral emissions during multiple close flybys following Juno’s orbital insertion on 5 July 2016. Each perijove provides a different snapshot of the Jovian auroral emissions recorded at different system III longitudes and local time conditions. We present the analysis of an auroral feature identified in Jupiter’s polar region by Juno-UVS, characterized by faint (~100 kR) concentric circles of UV emission expanding with time. The features were found within Jupiter’s polar auroral regions, i.e. inside of the main oval, both in the northern and southern hemispheres. These regions, connected to Jupiter’s outer magnetosphere, are the most dynamic part of Jupiter’s UV-aurora often exhibiting flares evolving over short timescales. As Juno spins at a rate of 2 rpm, UVS provides snapshots of regions smaller than the main auroral regions. Consecutive spins recorded over the same region allow identification and characterization of these auroral features. We characterize where the “raindrops”-like features occur within the auroral region and determine their expansion rates. We use the Vogt et al. (2011, 2015) magnetosphere-ionosphere mapping model coupled with the JRM09 magnetic field model to trace the origin of these emissions back to their origin in the magnetodisk. We discuss potential physical interpretations of such features. [less ▲]

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See detailA Keogram Analysis of Local Time Variations of Jupiter’s Ultraviolet Aurora using Juno UVS Observations
Greathouse, Thomas; Gladstone, Randy; Versteeg, Maarten et al

Poster (2019, December 11)

With 20 successfully completed Perijoves, Juno UVS has collected an enormous amount of data with unprecedented views of the northern and southern auroras spanning all local time geometries. Juno UVS, with ... [more ▼]

With 20 successfully completed Perijoves, Juno UVS has collected an enormous amount of data with unprecedented views of the northern and southern auroras spanning all local time geometries. Juno UVS, with its spectral and spatial mapping capabilities allows for the retrieval of both UV brightness as well as color ratio information. Maps of both the brightness and color ratio of the main ovals and polar emissions display strong local time variations, some suggestive of ionospheric local time control while others magnetosphere local time drivers. In an attempt to quantitatively track the evolution of the auroral emission morphology and intensity, we have developed a process to create keograms of Jupiter’s auroral emissions. The keograms display a complicated evolution of northern and southern auroral emissions that depend not only on local time, but also on the overall state of the magnetosphere which varies perijove to perijove. We will present our method of producing the keograms and discuss insights we have drawn from them. Additionally, we present an attempt to trace the origin within the magnetodisk of the observed emissions via magnetic flux mapping using the Vogt et al. 2015 model updated to include the JRM09 magnetic field model. [less ▲]

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