Discrete Energy Bands Beyond Galilean Moons: Bounce-Phase Structuring of Jovian Magnetospheric Particles

Discrete energy bands of ion fluxes, typically organized in velocity with equal separations, have been frequently observed in Jupiter’s magnetosphere either in association with Galilean moons or in regions far from their influence. Here, we focus on the latter and propose that these bands are manifestations of bounce-phase structuring, analogous to drift-phase structuring responsible for the well-known zebra-stripe patterns. In our proposed framework, latitude-dependent electric-field perturbations interact with ions at different bounce phases, producing phase-dependent energy modulations. As the ions continue to bounce at their respective bounce frequencies, which scale with ion velocity, these modulations naturally evolve into discrete, velocity-ordered banded structures. We examine several potential sources of latitude-dependent electric fields, including impulsive disturbances and wave-related processes. Test-particle simulations reproduce the key observational features. These results support bounce-phase structuring as a unifying interpretation of both non-moon and moon-associated discrete bands, and provide a new diagnostic perspective on Jovian magnetospheric dynamics.