Plasma Sheet Boundary Layer in Jupiter's Magnetodisk as Observed by Juno

Abstract

The Juno spacecraft has been orbiting Jupiter for the past 3 years. During this interval, Juno has collected large datasets of plasma, magnetic field, and wave measurements in Jupiter's magnetosphere. In this study, we conduct statistics on the plasma and wave characteristics in Jupiter's magnetodisk (nightside magnetosphere beyond 20 Jupiter radii, RJ). Distributions of electron fluxes and waves in the magnetodisk exhibit different characteristics in two regions: the plasma sheet with dense plasma and weak wave intensity and the plasma sheet boundary layer (PSBL) occupied by strong waves and rarefied plasma. We discuss that these waves can be generated by field‐aligned high‐energy electrons in the PSBL. We further compare plasma and wave properties in the PSBL of Jupiter's magnetodisk with the PSBL in Earth's magnetotail. This comparison suggests that the PSBL in Jupiter's magnetodisk may be formed by transient magnetic reconnection in the Jovian magnetosphere. The dawn‐dusk asymmetry of the PSBL properties further supports this scenario: the PSBL is more pronounced in the dawn flank of Jupiter's magnetodisk, where magnetic reconnection is predicted to occur by models of the rotation‐dominated magnetosphere. We further discuss properties of the Jovian PSBL and implications on magnetic reconnection in Jupiter's magnetosphere.

Energetic Electron Distributions Near the Magnetic Equator in the Jovian Plasma Sheet and Outer Radiation Belt Using Juno Observations

“…The higher frequency (∼500 Hz– f ce ) whistler‐mode waves with electric field intensification are observed in the higher latitude lobe region during 13–15 UT and 22–24 UT as reported by Zhang et al. (2020).…”

“…Electrostatic waves are observed with larger electric field intensities at lower frequencies near the plasma sheet (Figure 1e), without clear wave magnetic field intensifications (Figure 1f). The higher frequency (∼500 Hz-f ce ) whistler-mode waves with electric field intensification are observed in the higher latitude lobe region during 13-15 UT and 22-24 UT as reported by Zhang et al (2020). Using the measured magnetic fields, we selected the periods when Juno was near the magnetic equator at 𝐴𝐴 𝐴𝐴 𝐴 20𝐴𝐴𝐽𝐽 indicated by the blue bars between Figures 1d and 1e, using the method described below.…”

Energetic Proton Distributions in the Inner and Middle Magnetosphere of Jupiter Using Juno Observations

“…These available bins show that the flux is symmetric about the equator. In the following sections, we mainly focus on the near-equatorial regions at Jupiter (see magenta flags between panels a and b in Figure 1), which are selected as |MLAT| < 10° at M < 20, and further required to be located within magnetic field dips at M > 20 (near the magnetodisc), since magnetic field lines are more stretched at high M-shells due to the current sheet and cannot always be well captured by the field model (Phipps & Bagenal, 2021;Zhang et al, 2020). The magnetic dips are selected by requiring the observed magnetic field magnitude to be less than 0.8 times of the 1.5 hr running-averaged magnetic field magnitude.…”

Loss of Energetic Ions Comprising the Ring Current Populations of Jupiter's Middle and Inner Magnetosphere

“…Following insertion, the line-of-apsides has been slowly precessing southward (∼1° per orbit) and toward the nightside (∼4° per orbit). Figure 2 in Zhang et al (2020) provides a good sense regarding how the orbit evolves over time. JEDI measures energy, angle, and composition distributions of electrons (∼25-∼1,200 keV) and ions (protons: ∼10 keV to >4 MeV; oxygen and sulfur from Figures 1 and 2 are representative of a number of other figures that we show in this paper.…”