Energetic ions observed by Ulysses in the Jovian magnetosheath

In this paper we present a survey of energetic (>∼50 keV) ion and (>∼40 keV) electron measurements made in the Jovian magnetosheath by the (Heliospheric Instrument for Spectra, Composition and Anisotropy at Low Energies) experiment onboard Ulysses, during its flyby of Jupiter in February 1992. The most common characteristics of the magnetosheath ion events observed by Ulysses were found to be the following: (1) intensity gradients in the general direction of the magnetopause, (2) an outward ion streaming toward the bow shock, (3) almost continuous presence of magnetospheric electrons during times of enhanced ion fluxes, (4) lower intensities and harder spectra of energetic (∼0.05–∼2 MeV) ions in the magnetosheath than those in the adjacent outer magnetosphere, (5) a variation in ion and electron intensities with almost the planet rotation period (∼10 h), (6) a quasi-periodic ∼40 (or ∼10–20) min modulation in ion and electron intensity and anisotropy data, as in the Jovian magnetosphere. The magnetosheath ion characteristics strongly suggest that leakage of energetic particles from the magnetosphere controlled in general the >∼60 keV magnetosheath ion observations made by Ulysses. In particular, the observations suggest a strong contribution in magnetosheath ion fluxes from magnetospheric particles originating from the recently identified high latitude particle layer. Evidence of electron and low-energy (<∼300 keV) ion temporal trapping was found downstream from the quasi-perpendicular bow shock outbound. No effects of a diffusive type acceleration were found near the quasi-parallel bow shock inbound, under a radial magnetic field.