Plasma bulk flow in Jupiter's dayside middle magnetosphere

Abstract

Using the plasma data obtained during the Voyager 1 encounter and the full response function of the Plasma Science (PLS) experiment, convective plasma velocities have been determined in the dayside middle magnetosphere of Jupiter (10 R J < r < 25 R J ). We find that temperature anisotropies have very little effect on plasma velocity determination and that the plasma data are well approximated by converted, isotropic Maxwellian ion distribution functions. The insensitivity of the analysis to any thermal anisotropies which may exist allows a good determination of the bulk plasma flow velocity. In addition to the subcorotational azimuthal flow there exists a substantial nonazimuthal component of plasma flow. This nonazimuthal flow is mostly aligned (antialigned) with the local magnetic field but also exhibits a cross‐field component. The velocity pattern is inconsistent with enhanced plasma outflow in the active sector, as suggested by the corotating convection model of plasma transport. The contribution of field‐aligned flow along the curved magnetic field lines to the stress on the magnetic field is evaluated. In the region studied such flow contributes up to one half the stress produced by the azimuthal plasma flow.