ULYSSES PLASMA ELECTRON OBSERVATIONS IN THE JOVIAN MAGNETOSPHERE

The electron analyzer of the solar wind plasma experiment aboard the U lysses spacecraft measured the plasma properties of the Jovian magneto sphere and surrounding regions during the February 1992 encounter with Jupiter. In addition to sampling a new region of the Jovian magnetosp here, the Ulysses electron measurements were unique in that they inclu ded fine directional sampling over nearly 4pi sr in look direction, fo r 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 c rossed 10 times, with each crossing characterized by a boundary layer with mixed magnetospheric and magnetosheath-like electron distribution s. The spacecraft transited the dayside, prenoon, equatorial magnetosp here inbound, and the near-terminator, dusk magnetosphere at mid-latit udes outbound. The middle and inner magnetosphere contained a distinct plasma sheet, well-ordered in magnetic latitude, while the outer magn etosphere was less cleanly structured. Field-aligned electron anisotro pies were observed throughout the magnetosphere. Unique electron spect ra were seen in probable open-field line regions at the highest sample d magnetic latitudes in the inner magnetosphere. Azimuthal flow veloci ties indicated significant departures from rigid corotation, perhaps r epresenting a combination of corotation and tailward flow. Radial plas ma flows were slightly outward in the prenoon plasma sheet and strongl y outward throughout the dusk terminator region, but were inward at hi gher latitudes on the dayside. Strong southward flows were observed in the outer magnetosphere on the dusk side.