Comparing Electron Energetics and UV Brightness in Jupiter's Northern Polar Region During Juno Perijove 5

Ebert, R. W.; Greathouse, Thomas; Clark, G.; Allegrini, F.; Bagenal, F.; Bolton, S. J.; Connerney, J. E. P.; Gladstone, G. R.; Imai, Masafumi; Hue, V.; Kŭrth, W. S.; Levin, S. M.; Louarn, P.; Mauk, B. H.; McComas, D. J.; Paranicas, C.; Szalay, J. R.; Thomsen, M. F.; Valek, P. W.; Wilson, R. J.

doi:10.1029/2018gl081129

Cited by 22 publications

(36 citation statements)

References 34 publications

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“…PJ3‐N, PJ10‐N, and PJ11‐N show examples of electron flux‐auroral brightness structures where the peak of the JEDI energy flux is comparable to the corresponding UV flux but is significantly narrower and drops by more than an order of magnitude faster than the corresponding H 2 ‐derived energy flux. In contrast, the PJ5‐N ME crossing shows no excess H 2 auroral emission, in agreement with the comparison with the JADE measurements by Ebert et al (). PJ7‐S shows some excess JEDI flux at 2:34 when crossing the field lines threading the ME.…”

Section: Discussionsupporting

confidence: 92%

Contemporaneous Observations of Jovian Energetic Auroral Electrons and Ultraviolet Emissions by the Juno Spacecraft

et al. 2019

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We present comparisons of precipitating electron flux and auroral brightness measurements made during several Juno transits over Jupiter's auroral regions in both hemispheres. We extract from the ultraviolet spectrograph (UVS) spectral imager H 2 emission intensities at locations magnetically conjugate to the spacecraft using the JRM09 model. We use UVS images as close in time as possible to the electron measurements by the Jupiter Energetic Particle Detector Instrument (JEDI) instrument. The upward electron flux generally exceeds the downward component and shows a broadband energy distribution. Auroral intensity is related to total precipitated electron flux and compared with the energy-integrated JEDI flux inside the loss cone. The far ultraviolet color ratio along the spacecraft footprint maps variations of the mean energy of the auroral electron precipitation. A wide diversity of situations has been observed. The intensity of the diffuse emission equatorward of the main oval is generally in fair agreement with the JEDI downward energy flux. The intensity of the ME matches exceeds or remains below the value expected from the JEDI electron energy flux. The polar emission may be more than an order of magnitude brighter than associated with the JEDI electron flux in association with high values of the color ratio. We tentatively explain these observations by the location of the electron energization region relative to Juno's orbit as it transits the auroral region. Current models predict that the extent and the altitude of electron acceleration along the magnetic field lines are consistent with this assumption.The main auroral emission (ME) or "auroral oval" is a zone of emission encircling, sometimes only partially, Jupiter's magnetic poles. This "ring" of emission is rather stable on time scales of minutes to hours (Grodent,

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Section: Discussionsupporting

confidence: 92%

Contemporaneous Observations of Jovian Energetic Auroral Electrons and Ultraviolet Emissions by the Juno Spacecraft

et al. 2019

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“…Finally, note that other studies by Ebert et al (2019) and Gérard et al (2019) find times when the energy flux is correlated with the UV brightness at the magnetic foot point of Juno and also other times when it does not, probably for similar reasons.…”

Section: Resultsmentioning

confidence: 61%

Energy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission

et al. 2020

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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 (<10 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 R J . Outside that region, the >100-keV electrons contribute to most (>~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.

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“…JEDI is a complement to the lower energy Jupiter Auroral Distributions Experiment (JADE) instrument, which measures distributions of electrons from 100 eV to 100 keV, and of ions with composition up to 46 keV/q, where q is electric charge (McComas et al, 2017). Some initial results from the JADE instrument over auroral regions and the polar caps are provided by Allegrini et al (2017), Ebert et al (2017Ebert et al ( , 2019, and Szalay et al (2017). Of special importance to our investigation here is the magnetometer measurements (Connerney, Benn, et al, 2017), which allow particle measurements to be ordered by pitch angle (angle between the particle velocity vector and the magnetic field vector).…”

Section: Juno Measurementsmentioning

confidence: 99%

Energetic Particles and Acceleration Regions Over Jupiter's Polar Cap and Main Aurora: A Broad Overview

et al. 2020

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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. Plain Language Summary The science objectives of the Juno mission, with its spacecraft now orbiting Jupiter in a polar orbit, include understanding the space environments of Jupiter's polar regions and generation of Jupiter's uniquely powerful aurora. In Jupiter's polar cap regions (poleward of the main auroral oval encircling the northern and southern poles), we find here that (1) beams of electrons aligned with the upward magnetic field direction are ever-present with energies extended to the 100s to 1,000s of kilo electron volts and (2) downward magnetic field-aligned electrostatic potentials reaching greater than a million volts occur over broad regions for 80% of the polar cap crossings. For the main auroral oval, we find three distinct zones: designated here as diffuse aurora (DifA), Zone-I (ZI(D)) showing downward electron acceleration to 100s of kiloelectron volts, and Zone-II (ZII(B)) showing bidirectional acceleration with the upward intensities often greater than downward intensities. ZI(D) sometimes shows upward electrostatic potentials reaching 100s of kilovolts and is associated with upward magnetic field-aligned electric currents. ZII(B) sometimes shows downward electrostatic potentials reaching 100s of kilovolts and is associated with downward electric currents. Unexpectedly from Earth studies, ZI(D) and ZII(B) ar...

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Comparing Electron Energetics and UV Brightness in Jupiter's Northern Polar Region During Juno Perijove 5

Cited by 22 publications

References 34 publications

Contemporaneous Observations of Jovian Energetic Auroral Electrons and Ultraviolet Emissions by the Juno Spacecraft

Contemporaneous Observations of Jovian Energetic Auroral Electrons and Ultraviolet Emissions by the Juno Spacecraft

Energy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission

Energetic Particles and Acceleration Regions Over Jupiter's Polar Cap and Main Aurora: A Broad Overview

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