Ulysses paper

Planet. Space Sci., 45, 1143-1170, 1997

Abstract:
Field-perpendicular first order anisotropies of energetic ions may be due either to plasma flows transverse to the magnetic field (the ECB drift) or to spatial gradients in the ion flux. Here we present a technique which separates these sources of anisotropy by examining the dependence of the latter on ion energy. We apply this technique to data obtained by the Anisotropy Telescopes instrument on the Ulysses spacecraft during the Jupiter flyby in February 1992, using data from adjacent proton channels centred at 1.0 and 1.75 MeV. The results provide a continuous monitoring of both the field-transverse plasma flow and the spatial gradient of ~1 MeV protons along the flyby trajectory, which traversed the near-equatorial prenoon magnetosphere inbound and the dusk magnetosphere at moderate southerly latitudes outbound. We show that during the Ulysses flyby the flux gradient effect contributed significantly to the first order anisotropy of ~1 MeV protons in all the magnetospheric regions sampled, and was generally dominant in the middle magnetosphere plasma-current sheet (where the e-folding scale length was ~1 R_J), and on field lines inferred to be mapping thereto. Our results on plasma velocities may be summarised as indicating antisunward flow at ~200 kms-1 in the outer magnetosphere (a region ~30 R_J wide in the equatorial plane inside the magnetopause), while the plasma inside this in the middle magnetosphere plasma sheet flowed sunwards at similar speeds. The latter statement applies over a ~30 R_J-wide region of the equatorial plasma-current sheet from the outer edge at 70-80 R_J inwards to ~45 R_J, the latter being the minimum equatorial distance of observations of these field lines due to the off-equatorial nature of the spacecraft trajectory.

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