Radial Evolution of Electron Pitch Angle Distributions in the Inner Part of Jovian Magnetosphere

Previous observations in Jupiter's magnetosphere have revealed that the pitch-angle distributions (PADs) of energetic ((Formula presented.) keV) electrons transition from pancake to field-aligned distributions from (Formula presented.) 10 to 20 Jupiter radii. Here, by analyzing Juno/JADE-E data, we show that a similar transition also occurs for electrons at energy (Formula presented.) 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.