On the energy source for diffuse Jovian auroral emissivity

Abstract

42 ke V) ion distributions in the middle magnetosphere (9 < RJ < 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 ke V) 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 ≤ RJ ≤ 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 RJ. 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 (Bw ≥ 25 pT or Ew ≥ 5 mV/m) are sufficient to induce strong diffusion scattering outside 10 RJ. Such scattering can account for energy deposition over a broad latitude range (△λ≥5°) associated with the diffuse Jovian aurora.