Yash Sarkango

In this study, we propose a new mechanism to explain the observed particle flux at discrete energies in the flux tubes connecting to the wakes of the Galilean moons, first reported by Sarkango et al. (2024, https://doi.org/10.1029/2023gl107431 ) and referred to as “banded flux.” We demonstrate the proposed mechanism using test particle simulations. Sarkango et al. (2024, https://doi.org/10.1029/2023gl107431 ) propose a bounce resonance mechanism for the formation of the banded flux. However, the mechanism has not been tested numerically or analytically. In contrast, Yang et al. (2025, https://doi.org/10.1029/2024gl112240 ) propose that absorption at the moons' surfaces is responsible for the banded flux observed in the wakes of the moons. In this study, the mechanism proposed by Yang et al. (2025, https://doi.org/10.1029/2024gl112240 ) is tested using test particle simulations for the first time, and the limitations of both mechanisms are discussed. According to our proposed mechanism, the observed banded flux could result from an oscillatory parallel electric field . This is generated by the electron inertial effect in the low density region at high latitudes. The oscillatory nature of arises from multiple secondary reflections at density gradients of the Io plasma torus and the ionosphere. These reflections produce an alternating pattern with longitude and opposite polarity on either side of the M‐shell of the moon's foot point, as seen from the moon's reference frame. At a fixed location in the corotating frame, exhibits a quasi‐periodic temporal pattern.

Thermal electrons in Jupiter's magnetodisc have been observed to be anisotropic with higher parallel temperature compared to perpendicular. In this work, we used previously‐derived electron properties (Sarkango et al., 2025, https://doi.org/10.1029/2025gl118209 ) to calculate electron and compared the observed anisotropy with electron temperature‐anisotropy‐driven instability thresholds. For cold electrons, the ratio of perpendicular to parallel temperatures decreased with M‐shell, reached a minimum near M = 20–25, beyond which it increased until the distribution was quasi‐isotropic. In space, this turnover was observed close to the oblique electron firehose instability threshold. Linear dispersion analysis using plasma parameters representative of different M‐shells predicts the onset of the oblique firehose instability arising primarily due to cold electron anisotropy, though growth rates differ based on the cold and hot electron abundances, anisotropies, and . On the basis of these observations, we argue that the cold electron anisotropy in Jupiter's magnetodisc is regulated by the oblique electron firehose instability, which may be a source of plasma waves and could contribute to cyclotron‐resonant heating of the Jovian plasma.

Jupiter displays the brightest auroras in the solar system, driven by intensely varying energetic electrons that accelerate into the atmosphere. Here, we provide a comprehensive formalism that accurately describes the bimodality of observed auroral electron acceleration regimes. We demonstrate that the occurrence of the two dominant auroral regimes—broadband and monoenergetic—is dictated by specific characteristic plasma length scales, namely, the relationship between the transverse length scale and the electron inertial length. Furthermore, in contrast to the long-standing acceptance that Alfvén waves responsible for auroral electron acceleration exclusively originate at distant equatorial regions, we demonstrate that they can be locally generated at Jupiter’s low altitudes. From this understanding, we find that locally generated, low-altitude Alfvén waves can be directly responsible for accelerating the most intense auroral electrons at Jupiter. These findings establish that the low-altitude acceleration region can itself become a source of Alfvén waves rather than merely a sink for wave energy, thus altering the standard picture of global magnetospheric energy transfer in strongly magnetized planets.

Thermal electrons in Jupiter's magnetodisc have been observed to be anisotropic with higher parallel temperature compared to perpendicular. In this work, we used previously-derived electron properties (Sarkango et al. 2025) to calculate electron β _∥ and compared the observed anisotropy with electron temperature-anisotropy-driven instability thresholds. For cold electrons, the ratio of perpendicular to parallel temperatures (T _⊥ /T _∥ ) decreased with M-shell, reached a minimum near M=20-25, beyond which it increased until the distribution was quasi-isotropic. In T _⊥ /T _∥ -β _∥ space, this turnover was observed close to the oblique electron firehose instability threshold. Linear dispersion analysis using plasma parameters representative of different M-shells predicts the onset of the oblique firehose instability arising primarily due to cold electron anisotropy, though growth rates differ based on the cold and hot electron abundances, anisotropies, and β _∥ . On the basis of these observations, we argue that the cold electron anisotropy in Jupiter's magnetodisc is regulated by the oblique electron firehose instability, which may be a source of plasma waves and could contribute to cyclotron-resonant heating of the Jovian plasma.

Thermal electrons in Jupiter's magnetodisc have been observed to be anisotropic with higher parallel temperature compared to perpendicular. In this work, we used previously-derived electron properties (Sarkango et al. 2025) to calculate electron β _∥ and compared the observed anisotropy with electron temperature-anisotropy-driven instability thresholds. For cold electrons, the ratio of perpendicular to parallel temperatures (T _⊥ /T _∥ ) decreased with M-shell, reached a minimum near M=20-25, beyond which it increased until the distribution was quasi-isotropic. In T _⊥ /T _∥ -β _∥ space, this turnover was observed close to the oblique electron firehose instability threshold. Linear dispersion analysis using plasma parameters representative of different M-shells predicts the onset of the oblique firehose instability arising primarily due to cold electron anisotropy, though growth rates differ based on the cold and hot electron abundances, anisotropies, and β _∥ . On the basis of these observations, we argue that the cold electron anisotropy in Jupiter's magnetodisc is regulated by the oblique electron firehose instability, which may be a source of plasma waves and could contribute to cyclotron-resonant heating of the Jovian plasma.

The mechanism driving ion outflow from Jupiter's auroras remains to be determined. outflow has been observed with highly field‐aligned pitch angles consistent with acceleration by high‐altitude electrostatic potential structures. However, the cold ionospheric ions require a pre‐acceleration mechanism to reach Jupiter's large escape speed and access the potential structures. Here we present case studies of outflow coincident with intense ion cyclotron waves (ICWs). We invoke resonant wave heating to suggest a causality between the two phenomena. We further investigate Landau resonance with auroral electron beams as a plausible source of free energy using cold plasma theory, finding that electron energies between 10 and 100 keV produce results consistent with ICW observations. and ICWs are likewise present, which we suggest indicates that Jovian ion outflow is a multi‐species process.

The mechanism driving ion outflow from Jupiter’s auroras remains to be determined. H+ outflow has been observed with highly field-aligned pitch angles consistent with acceleration by high altitude potential structures. However, the cold ionospheric ions require a pre-acceleration mechanism to reach Jupiter’s large escape speed and access the potential structures. Here we present a case study of H+ outflow coincident with intense upward propagating H+ ion cyclotron waves (ICWs). We invoke resonant wave heating to suggest a causality between the two phenomena. We further investigate Landau resonance with auroral electron beams as a plausible source of free energy using cold plasma theory, finding that electron energies between 10-100 keV produce results consistent with ICW observations. H2+ and H3+ ICWs are likewise present, which we suggest indicates that Jovian ion outflow is a multi-species process.

Previous observations in Jupiter's magnetosphere have revealed that the pitch‐angle distributions (PADs) of energetic ( keV) electrons transition from pancake to field‐aligned distributions from 10 to 20 Jupiter radii. Here, by analyzing Juno/JADE‐E data, we show that a similar transition also occurs for electrons at energy keV. This feature is persistent, observed over a span of 6 years and across all nightside local times. Further analysis reveals that the transition occurs at larger M‐shells for higher‐energy electrons and at greater distances from the equatorial plane, placing strong constraints on the underlying mechanisms. By developing a model based on Liouville's theorem and the conservation of adiabatic invariants, we show that adiabatic radial transport can reproduce these features, suggesting it as a mechanism driving the observed PAD transition. However, the noted discrepancies in absolute flux between observations and the modeling results suggest non‐adiabatic effects may still play a role in electron dynamics.

Despite their importance to a variety of plasma processes in Jupiter's magnetosphere, properties of the thermal and suprathermal electrons have been sparsely reported in past literature. To address this gap, we used data from Juno 's Jovian Auroral Distributions Experiment Electron sensors to survey electron properties in Jupiter's magnetodisc between M‐shells of M = 9–40 and magnetic latitudes less than 20° within years 2016–2023. We fit the electron measurements with a sum of two anisotropic kappa distributions and provide estimates of the electron density, temperature, anisotropy, and thermodynamic kappa for the cold and hot populations, separately. We find that the electron temperature increases non‐adiabatically with M‐shell and the cold electron temperature anisotropy is most extreme near M = 15. We also provide estimates of the ambient electron properties near the Galilean moons, which should be treated with caution considering the many caveats of the fitting process, which is often associated with large uncertainties.