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AGU: Journal of Geophysical Research, Space Physics

 

Keywords

  • Saturn
  • magnetosphere
  • ions

Index Terms

  • Magnetospheric Physics: Planetary magnetospheres
  • Magnetospheric Physics: Magnetosphere: inner
  • Planetary Sciences: Fluid Planets: Magnetospheres
  • Magnetospheric Physics: Magnetospheric configuration and dynamics
Abstract
Cited By (31)
 

Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, A12218, 11 PP., 2008
doi:10.1029/2008JA013486

Cassini plasma spectrometer thermal ion measurements in Saturn's inner magnetosphere

R. J. Wilson

Space and Atmospheric Sciences Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

R. L. Tokar

Space and Atmospheric Sciences Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

M. G. Henderson

Space and Atmospheric Sciences Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

T. W. Hill

Department of Physics and Astronomy, Rice University, Houston, Texas, USA

M. F. Thomsen

Space and Atmospheric Sciences Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA

D. H. Pontius Jr.

Physics Department, Birmingham-Southern College, Birmingham, Alabama, USA

Plasma data from the Cassini Plasma Spectrometer experiment are analyzed using a robust forward modeling technique for dayside equatorial orbits within the range 5.5 to 11 Saturn radii (1 RS = 60,268 km). It is assumed the measured ion data may be represented by two anisotropic Maxwellian distributed species, H+ and a water group ion, W+. Saturn's magnetospheric plasma is shown to subcorotate by 15–30% below rigid corotation within this region, with a minimum in fractional lag between 7 and 9 RS. There is a suggestion of a small radial outflow, but the selection of data for this study precluded the inclusion of interchange injection events. Ion densities are in excellent agreement with the Cassini plasma wave instrument, giving confidence in the forward modeling technique. Plasma moments including density, temperatures, and velocities are presented, along with empirical models for density and azimuthal velocity. Water group temperature anisotropies T ⊥ /T ∥ have values between 3 and 8 near 5.5 RS, becoming less anisotropic as distance increases, but are still not isotropic by 10 RS. The implications of these results for mass loading in the Saturnian magnetosphere are discussed, with the conclusion that an important fraction of the plasma source is located inside of the 5.5 RS boundary of this study.

Received 12 June 2008; accepted 17 September 2008; published 31 December 2008.

Citation: Wilson, R. J., R. L. Tokar, M. G. Henderson, T. W. Hill, M. F. Thomsen, and D. H. Pontius Jr. (2008), Cassini plasma spectrometer thermal ion measurements in Saturn's inner magnetosphere, J. Geophys. Res., 113, A12218, doi:10.1029/2008JA013486.

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