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

Abstract

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,

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

“…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.…”

“…JEDI has “witness” detectors that give a qualitative sense, but not a quantitative subtraction value, of the occurrence of penetrating electrons. Thus, it is likely that the energy flux in the first few minutes of this interval is overestimated due to penetrating radiation (see also Gérard et al, 2019). That would explain why the UV emissions stay dim while the total downward energy flux increases toward lower absolute latitudes.…”

First Report of Electron Measurements During a Europa Footprint Tail Crossing by Juno

“…The LC angle is about 35° at the time of the crossing. The green data points are estimates of the UV brightness at Juno's magnetic footprint measured between 155 and 162 nm and multiplied by 8.1 to reflect for the total brightness emitted in the total H2 Lyman and Werner band systems (~80 to ~170 nm; Gérard et al, 2019; Gustin et al, 2013). We calculate the average UV brightness in a 0.1° radius around Juno's magnetic footprint (which corresponds to a radius of ~55 km for this time), in a similar manner as in Allegrini et al (2020).…”

Alfvénic Acceleration Sustains Ganymede's Footprint Tail Aurora

“…Ganymede orbits Jupiter at 15 Jovian radii ( R J ), twice per orbit crossing Jupiter's current sheet that distends the magnetospheric magnetic field and makes it difficult to precisely trace magnetic field lines from its location to the Jovian atmosphere. Instead of correlating features in Juno plasma data to their equatorially mapped regions as done previously (e.g., Allegrini et al, ; Szalay et al, ), we link in situ measurements of particles and fields with near‐simultaneous UV images of the Jovian auroral emissions (e.g., Ebert et al, ; Gérard et al, ).…”