Circulation and dynamics in the jovian magnetosphere Original Research Article

Io continually adds mass to the Io torus and this density builds up until centrifugal force is sufficient to overcome the line tying of the jovian ionosphere. The magnetic flux is carried outward with this slow radial convection. Under the assumption that 1 ton per second is added to the torus at Io and that the Voyager observed densities and average ion mass are pertinent for the Pioneer and Galileo epochs, a consistent flow pattern arises. The outward flow near Io is a few meters per second. Near Europa the velocity, based on the observations of a Europa plume, rises to about 400 m/s. Beyond 24 RJ in the magnetodisk it is possible to again estimate the velocity. It is about 20 km/s at 25 RJ and about 50 km/sec at 40 RJ consistent with the Voyager LECP measurements. This outflow of magnetic flux is replenished by reconnection of magnetic flux in the near tail and the subsequent inward convection of empty flux tubes into the inner magnetosphere. These flux tubes are seen in the middle magnetosphere and the Io torus. Their scarcity as judged by the fact that they constitute only about 0.4% of the observing time indicates that they are moving inward at a much higher rate than the mass-loaded magnetospheric plasma moves outward. In the neighborhood of the magnetodisk the outflow appears not to be steady as the magnetic flux crossing the current sheet varies greatly from orbit to orbit. This unsteadiness may lead the occasional auroral storms seen in the ionosphere at the feet of these field lines.