4.2.2 Equatorial profiles

Figure 6 shows the plasma parameters at the centrifugal equator extrapolated from data measured along the spacecraft trajectory using equations (10) and (12), with $\kappa=2$ and $A_0=3$ for the ions, and $\kappa_e=2.4$ (measured by Ulysses) and $A_{0e}=1.2$ (after [ Sittler and Strobel, 1987]) for the electrons. These radial profiles along the centrifugal equator derived using our bi-kappa model are significantly different from those obtained by Bagenal [1994] [see her Figures 5& 6 ] at radial distances greater than 8${\rm R_J}$ where the Voyager 1 spacecraft was well below the centrifugal equator. Indeed because the bi-kappa distribution produces a stronger confinement of the plasma to the centrifugal equator than Maxwellian distributions, the equatorial densities are substantially enhanced beyond 8${\rm R_J}$.

Figure 6: Densities and temperatures extrapolated from Voyager 1 to the centrifugal equator, using a bi-kappa function velocity distributions for the particles. ( $\kappa \equiv 2, A_0\equiv 3$ for all the ions, $\kappa _e=2.4, A_{0e}=1.2$ for the electrons). We show here the total densities (top) and the perpendicular temperatures (bottom); electrons are in black, sulfur in red, oxygen in blue and protons are in green. We have superposed the former core+halo ion temperature(pink dotted line) and adiabatic gradients (orange dashed lines) decreasing as $L^{-4}$ or as $L^{-3}$ for the densities and as $L^{-8/3}$ or as $L^{-3}$ for the temperatures.

The flatter radial profile of density has important implications for the radial diffusion of plasma in the torus [ Siscoe and Summers, 1981]. Of even greater significance, perhaps, is the difference in radial temperature profiles produced by the two models illustrated by the bottom panels of Figures 4 and 6.