Ulysses paper

J. Geophys. Res., 101, 15197, 1996

Abstract:
We discuss the large-scale flow in the Jovian magnetosphere based on recent observations during the flyby of the Ulysses spacecraft, combined with previous results from the Pioneer and Voyager encounters. A picture emerges in which rigid corotation (to within a few percent) is enforced by coupling to the ionosphere and atmosphere in the inner magnetosphere, out to 10-15R_J, follwed by a plateauing of the azimuthal flow at 150-250 km s^-1 in the middle magnetosphere plasma sheet at distances beyond ~20 R_J. Such conditions extend throughout the plasma sheet to distances of ~45 R_J on the dayside in the case of the compressed magnetosphere observed by the Voyagers and to ~70 R_J for the expanded system observed by Ulysses. Such flows may reasonably be accounted for on the basis of simple magnetosphere-ionosphere coupling models of planetary angular momentum transfer, though there is as yet no clear evidence for the transition region-outer magnetosphere, a different flow regime is observed which indicates the prescence of additional dynamical processes internal to the magnetosphere. The flows on both dawn and dusk flanks are directed antisunward at speeds of several hundred km s^-1 (say typically ~500 km s-1), while in the prenoon sector they appear to depend on the state of the magnetosphere , being in the sense of cortation at speeds 300-500 km s^-1 in the compressed state observed by the Voyagers, and at ~250 km s^-1 in the sense of anticorotation (and radially in) in the expanded state observed by Ulysses. These observations are briefly discussed in relation to ideas on rotationally-driven planetary winds. We also comment on the related azimuthal magnetic field perturbations which were observed by Ulysses in the various flow regimes and discuss them in relation to expectations based upon the transmission of angular momentum between the magnetosphere and ionosphere.

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