HR: 08:00h
AN: P51D-01    [Abstracts]
TI: A Diffusive Equilibrium Density Model for a Two-Species Plasma in Saturn's Magnetosphere
AU: * Persoon, A M
EM: ann-persoon@uiowa.edu
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Gurnett, D A
EM: donald-gurnett@uiowa.edu
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Santolik, O
EM: os@ufa.cas.cz
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Santolik, O
EM: os@ufa.cas.cz
AF: Inst. Atmospheric Physics, Charles University, Prague, CZ-18000, Czech Republic
AU: Kurth, W S
EM: william-kurth@uiowa.edu
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Groene, J B
EM: joseph-groene@uiowa.edu
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Faden, J B
EM: jeremy-faden@uiowa.edu
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AB: Measurements of the upper hybrid resonance frequency by the Radio and Plasma Wave Science (RPWS) instrument have been used to derive electron densities for more than 50 Cassini passes through Saturn's inner magnetosphere between July 1, 2004 and September 1, 2007. As the latitudinal and radial distributions of these density measurements have expanded, increasingly more complex density models have been developed to describe the distribution of plasma inside L=9. The early radial outflow model [Persoon et al., Geophys. Res. Lett., 32, L23105, 2005] found that the electron density has a radial dependence of R^{- 3.63}, but the model was restricted to density measurements in the equatorial plane. As density measurements at higher latitudes became available, a simple centrifugal potential model [Persoon et al., Geophys. Res. Lett., 33, L18106, 2006] was developed for the plasma distribution along the planetary magnetic field lines. This early centrifugal potential model, however, had a limited latitudinal distribution and was able to resolve only one ion species in the plasma distribution. Recent plasma density measurements acquired at higher latitudes have made it possible to resolve two distinct plasma components, assumed to be the water group ions (W+) and the hydrogen ions (H+). When compared to the centrifugal potential model, the density measurements for 5<L<9 yield a good fit to an equatorial density profile that varies as L^-4 R_S for the water group ions and as L^-5 R_S for the hydrogen ions and plasma scale heights that vary as (0.1)L^1.3 R_S for the water group ions and (0.3)L^1.3 R_S for the hydrogen ions, where R_S is the radius of Saturn. Although centrifugal force is the dominant force acting on the co-rotating plasma at these radial distances, the ambipolar electric field force becomes increasingly significant at higher latitudes and must be considered in a credible plasma density model for Saturn's magnetosphere. Plasma densities and anisotropies are determined from the comparison of the RPWS densities to a diffusive equilibrium model, derived from a solution to the full force balance equation for a plasma distribution along Saturn's magnetic field lines, originally presented by Richardson and Sittler [ J. Geophys. Res., 95, 12019, 1990] using the Voyager data. A contour plot of the plasma density in Saturn's inner magnetosphere is constructed from the fit of the electron density measurements to the diffusive equilibrium model.
DE: 2756 Planetary magnetospheres (5443, 5737, 6033)
DE: 5737 Magnetospheres (2756)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting