On the energy source for diffuse Jovian auroral emissivity

Data from the Energetic Particle Detector on Galileo have been used to investigate whether the radiation belt population can act as a direct energy reservoir for Jovian auroral emissions. Energetic (E > 42 keV) ion distributions in the middle magnetosphere (9 < R J < 26) yield peak precipitation energy fluxes comparable to a few ergs‐cm −2 ‐s −1 , which are too weak to produce significant auroral emissivity. Detailed analysis of energetic electrons (15‐884 keV) indicates the presence of an enhanced population near the loss cone that may provide precipitation energy flux above 10 ergs‐cm −2 ‐s −1 over an extended region (10 ≤ R J ≤ 25) of the middle magnetosphere. The available precipitation electron energy flux decreases at higher radial distance, falling to values below 1 erg‐cm −2 ‐s −1 outside 30 R J . Additional acceleration mechanisms such as field‐aligned currents are required to account for observed auroral intensities at higher L. The precipitation flux values presented here have been calculated under the assumption of strong pitch‐angle scattering due to wave‐particle interactions in the essentially collisionless middle magnetosphere. Plasma waves with relatively modest amplitude (B w ≥ 25 pT or E w ≥ 5 mV/m) are sufficient to induce strong diffusion scattering outside 10 R J . Such scattering can account for energy deposition over a broad latitude range (Δ λ ≥5 °) associated with the diffuse Jovian aurora.