Ulysses plasma electron observations in the Jovian magnetosphere

The electron analyzer of the solar wind plasma experiment aboard the Ulysses spacecraft measured the plasma properties of the Jovian magnetosphere and surrounding regions during the February 1992 encounter with Jupiter. In addition to sampling a new region of the Jovian magnetosphere, the Ulysses electron measurements were unique in that they included fine directional sampling over nearly 4π sr in look direction, for electron energies up to 862 eV. In this paper we present an overview of electron bulk parameters and a sampling of distribution shapes for the magnetosphere and adjacent plasma regions. The magnetopause was crossed 10 times, with each crossing characterized by a boundary layer with mixed magnetospheric and magnetosheath-like electron distributions. The spacecraft transited the dayside, prenoon, equatorial magnetosphere inbound, and the near-terminator, dusk magnetosphere at mid-latitudes outbound. The middle and inner magnetosphere contained a distinct plasma sheet, well-ordered in magnetic latitude, while the outer magnetosphere was less cleanly structured. Field-aligned electron anisotropies were observed throughout the magnetosphere. Unique electron spectra were seen in probable open-field line regions at the highest sampled magnetic latitudes in the inner magnetosphere. Azimuthal flow velocities indicated significant departures from rigid corotation, perhaps representing a combination of corotation and tailward flow. Radial plasma flows were slightly outward in the prenoon plasma sheet and strongly outward throughout the dusk terminator region, but were inward at higher latitudes on the dayside. Strong southward flows were observed in the outer magnetosphere on the dusk side.