MEASUREMENT OF DIRECT-CURRENT ELECTRIC-FIELDS AND PLASMA-FLOW SPEEDS IN JUPITER MAGNETOSPHERE

During the encounter of Ulysses with Jupiter, we have measured two components of the dc electric field and deduced from them the flow speed in the lo torus, as well as the presence of a polar cap region and what we interpret as a cleft region. Within the torus the flow speed is approximately equal to the speed of a plasma corotating with Jupiter but has significant deviations. The dominant deviations have an apparent period of the order of Jupiter's rotation period, but this might be a latitudinal effect. Other important periods are about 40 min arid less than 25 min.