FIELD-ALIGNED CURRENTS IN THE JOVIAN MAGNETOSPHERE DURING THE ULYSSESFLYBY

The data recorded by the dual vector helium/fluxgate magnetometer flow n onboard the Ulysses spacecraft during the flyby of Jupiter in Februa ry 1992 are analysed with the aim of identifying the presence of field -aligned current signatures. Field-aligned current flow is expected wh erever stress is being transmitted electromagnetically along the magne tic field direction. Sources of such currents at Jupiter are departure s within the magnetosphere from corotation, momentum transfer from the solar wind, or centrifugally driven magnetospheric outflow. It is poi nted out that the azimuthal field component provides a simple first-or der means of monitoring the presence of currents, the currents occurri ng in regions where the azimuthal component changes significantly. The data from both inbound and outbound passes show evidence of ''leading '' and ''lagging'' azimuthal field signatures where the field bends ou t of the meridian, and which are signatures symptomatic of current sys tems associated with departures from corotation. On the outbound pass, the most intense signatures are found where the field switches from a configuration symptomatic of the field lagging corotation to a config uration representing the field leading. The latter configuration also corresponds to a tail-like displacement of the field and, indeed, the magnetometer data alone cannot distinguish the source of the current s ystem, which could be due to solar wind magnetosphere coupling or whic h may arise from internal stress imbalance.