Bulk flows of hot plasma in the Jovian magnetosphere: A model of anisotropic fluxes of energetic ions.

摘要

Since the Ulysses flyby of Jupiter in February 1992, attempts to understand the bulk flows of hot plasma in the planet's magnetosphere have not given a consistent picture. The present study reports a comprehensive analysis of energetic particle anisotropies from the Ulysses mission. An empirical model has been developed which separates particle flow from particle gradient anisotropies. The model employs a multidimensional minimization routine to fit 13 free parameters simultaneously, using 98 measurements. The large number of independent measurements is possible because the Ulysses HI-SCALE instrument has nearly full angular coverage at high time resolution and moderately high angular resolution. The model uses the full energy-range ({dollar}sim{dollar}50-3000 keV/nuc) of the low energy magnetic spectrometers and also the pure proton channels of the composition aperture on the instrument. Flow results are presented for analysis periods which included both the inbound and outbound trajectories of the spacecraft. Results from the inbound pass, which occurred in the late morning sector, show a persistent radial flow away from Jupiter. The azimuthal velocity component is in the sense of planetary rotation but generally is belong rigid corotation. This corotational flow component is greater near the plasma current sheet than at higher magnetic latitudes. Outbound, the flows in the high latitude duskside magnetosphere as inferred from the particle anisotropies indicate, surprisingly, sunward flows opposite to planetary rotation. Evidence of gradient anisotropies have also been found; these gradient anisotropies are present throughout the Jovian magnetosphere, but the convected anisotropies dominate any density gradients. A picture is presented, consistent with the model results, in which the global magnetic field configuration and flows of hot plasma are dominated by subcorotation at low latitudes but by sunward flow at high latitudes.