Abstract
Abstract. Plasma waves observed in the Saturn magnetosphere provide an indication of the plasma population present in the rotationally dominated inner magnetosphere. Electrostatic cyclotron emissions often with harmonics and whistler mode emission are a common feature of Saturn's inner magnetosphere. The electron observations for a region near 5 RS outside and near a plasma injection region indicate a cooler low-energy (<100 eV), nearly isotropic plasma, and a much warmer (E>1000 eV) more pancake or butterfly distribution. We model the electron plasma distributions to conduct a linear dispersion analysis of the wave modes. The results suggest that the electrostatic electron cyclotron emissions can be generated by phase space density gradients associated with a loss cone that may be up to 20° wide. This loss cone is sometimes, but not always, observed because the field of view of the electron detectors does not include the magnetic field line at the time of the observations. The whistler mode emission can be generated by the pancake-like distribution and temperature anisotropy (T⊥/T||>1) of the warmer plasma population.
Highlights
Plasma waves in Saturn’s inner magnetosphere commonly include whistler mode emission and chorus emission as well as electron cyclotron emission with often one or more harmonics. Menietti et al (2008) have recently reported plasma waves within plasma injection regions that are frequently observed within 15 RS of Saturn
The electron distribution observed within these regions as observed in the inner magnetosphere consists of a tenuous warm plasma with T⊥/T||>1 and electron phase space density peaked near a pitch angle of 90◦ and a much cooler and more isotropic distribution
We model the electron distribution function to show that electron cyclotron (EC) emissions similar to those observed can be generated by a loss cone that is implicated in the data
Summary
Plasma waves in Saturn’s inner magnetosphere commonly include whistler mode emission and chorus emission as well as electron cyclotron emission with often one or more harmonics (cf. Gurnett et al, 2005; Hospodarsky et al, 2008). Menietti et al (2008) have recently reported plasma waves within plasma injection regions that are frequently observed within 15 RS of Saturn. Menietti et al.: Plasma waves observed in the inner Saturn magnetosphere and temperature anisotropies (T⊥/T||>1) in exciting whistler mode and chorus emission at Earth; and of narrow (only a few degrees) loss cones in generating ECH emissions. These latter authors argue that, for the terrestrial case, ECH waves scatter electrons into the loss cone to form the observed pancake distributions. Whistler-mode chorus at Earth consist of electromagnetic waves in the frequency range from a few hundred hertz to greater than 10 kHz observed in the lower density region outside the plasmapause These emissions are most often characterized as narrow-banded at f fce/2 with an emission gap near fce/2. Whistler mode emissions at frequencies similar to the observed emissions can be excited by the observed pancake distribution with a temperature anisotropy
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