Auroral Acceleration Generates Electron Beams in Jupiter's Middle Magnetosphere

TL;DR

This study analyzes electron beams in Jupiter's middle magnetosphere using Juno data, confirming their connection to auroral acceleration processes and providing insights into magnetospheric electron dynamics.

Contribution

It demonstrates the presence of narrow electron beams throughout Jupiter's middle magnetosphere and links them to auroral acceleration, using pitch angle distribution analysis and diffusion modeling.

Findings

Narrow electron beams are consistently observed across the magnetosphere.

Energy fluxes of these beams align with auroral electron acceleration.

Results support the hypothesis that middle magnetosphere beams originate from auroral regions.

Abstract

Observations made by the Juno spacecraft above Jupiter's polar regions have revealed that electrons accelerated toward Jupiter, which contribute to auroral emissions, are frequently accompanied by electrons accelerated away from Jupiter. These electrons should be observable as narrow electron beams in the middle magnetosphere, in accordance with the principles of adiabatic particle motion. The existence of such beams has been previously reported using data from the Galileo mission, and their relation to auroral processes has been hypothesized. In the present study, we analyze electrons measured by Juno's JEDI instrument in the middle magnetosphere between 13 RJ and 50.5 RJ radial distance and within energies of 30-1,200 keV. The pitch angle distributions of potential electron beams are fitted with an intensity 'beamness' function. The presence of narrow beams is demonstrated throughout the observation range. The energy fluxes of auroral and equatorial electron beams are compared by including pitch angle scattering processes along the magnetospheric field lines. This is achieved by solving the pitch angle diffusion equation for different sets of diffusion coefficients. The statistical occurrence distribution and the energy fluxes of the beams are consistent with auroral upward accelerated electrons observed in studies of the polar space environment. This finding provides further support for the hypothesis that the electron beams observed in the middle magnetosphere originate from the auroral acceleration region.