Analysis of Whistler‐Mode and Z‐Mode Emission in the Juno Primary Mission

Abstract

At the end of the Juno primary mission, we report observations of whistler mode chorus and Z‐mode emission. The Juno orbits are evolving and much better coverage of the whistler mode chorus source region has resulted since the earlier surveys. Bursty chorus emission extending to ∼30° latitude and to frequencies less than the lower hybrid frequency near the source region imply high electron energies (>100 keV). Average chorus intensity levels peak at ∼10−3 nT2 near M‐shell of 8–9 and magnetic latitude of ∼5°. Z‐mode emission is identified at higher latitudes generally near and inward of the Io torus with intensity levels as much as two orders of magnitude higher than Z‐mode emissions observed at Saturn. Inferred source regions for the Z‐mode are consistent with the inner edge of the Io torus and with auroral field lines that may also support Jovian kilometric and decametric emission. Parametric fitting functions are evaluated for both whistler mode chorus and Z‐mode, describing wave intensity as a function of frequency, magnetic latitude, and M‐shell. Both whistler mode and Z‐mode waves may have significant impact on electron scattering and acceleration at Jupiter as recent models indicate.

Wave and Particle Analysis of Z‐Mode and O‐Mode Emission in the Jovian Inner Magnetosphere

“…Similar procedures for identifying emission signatures at Jupiter have been demonstrated by Menietti et al. (2021), Sulaiman et al. (2021), Elliot et al.…”

“…We believe this most intense (red color) emission is ordinary mode (O-mode), which has a low-frequency cutoff at the plasma frequency. Similar procedures for identifying emission signatures at Jupiter have been demonstrated by Menietti et al (2021), Sulaiman et al (2021), Elliot et al (2021. Note also that the intense red emission intensity fades and the lower frequency cutoff increases at times when f pe increases (such as 19:08 to 19:12), indicating that it is probably a mixture of O-mode and Z-mode, since the Z-mode does not cutoff at f pe and can extend to higher frequency.…”

“…(2020) and Menietti et al. (2021) reported a survey of Z‐mode emission at Jupiter at middle latitudes in the region near and inward of M ∼ 10, with intensities that are about 50 times the magnitude of those previously observed at Saturn. Z‐mode at Saturn is believed to potentially accelerate electrons to MeV energies in the region inside the orbit of Enceladus through a Doppler‐shifted cyclotron resonance (Woodfield et al., 2018).…”

“…At Jupiter, the Z-mode emission is generally less intense and is usually observed at higher frequencies than whistler mode. Z-mode emission is observed at mid latitudes near the inner edge of the Enceladus plasma torus at Saturn, and at mid latitudes and near the inner edge of the Io torus at Jupiter (Menietti et al, 2018(Menietti et al, , 2021. Z-mode waves can efficiently scatter electrons and thus induce a stochastic acceleration (Horne & Thorne, 1998;Woodfield et al, 2018;Yu et al, 2019).…”

Diffusive scattering of energetic electrons by intense whistler-mode waves in an inhomogeneous plasma

“…Resonant electron interactions with whistler-mode waves are one of the main drivers of electron pitch-angle scattering and acceleration in various space plasma systems, e.g. solar flares (Bespalov, Zaitsev & Stepanov 1991;Filatov & Melnikov 2017;Melnikov & Filatov 2020), solar wind (Tong et al 2019;Cattell et al 2020Cattell et al , 2021Mozer et al 2021), shock waves (Hull et al 2012;Wilson et al 2013;Oka et al 2017;Page et al 2021), planetary radiation belts (Li et al 2021;Menietti et al 2021;Thorne et al 2021) and magnetic reconnection regions (Le Contel et al 2009;Breuillard et al 2016;Zhang et al 2018a). The basic theoretical framework for description of such interactions is the quasi-linear model (Drummond & Pines 1962;Vedenov, Velikhov & Sagdeev 1962;Andronov & Trakhtengerts 1964;Kennel & Engelmann 1966) that is based on the assumption of weak perturbation of particle dynamics by each single resonance.…”