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Electromagnetic ion‐cyclotron instability in the multi‐ion Jovian magnetosphere
Author(s) -
Thorne Richard M.,
Moses Julie
Publication year - 1983
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl010i008p00631
Subject(s) - magnetosphere , physics , jovian , atomic physics , instability , ion , cyclotron , geophysics , plasma , computational physics , astrophysics , saturn , nuclear physics , planet , quantum mechanics , mechanics
Propagation characteristics of electromagnetic ion‐cyclotron waves are extremely sensitive to the relative composition of thermal ions: this can consequently control the instability properties of resonant energetic ions in the Jovian magnetosphere. The dominance of heavy ions in the Io plasma torus will suppress ion‐cyclotron instability near the equatorial plane. Wave growth, however, can still occur away from the equator in the region where thermal hydrogen is expected to predominate. A theoretical assessment of the convective L‐mode gain indicates that Voyager 1 did not enter the preferred region of instability. Evidence for instability may nevertheless be available since oblique ion‐cyclotron waves are expected to experience a natural polarization reversal to the R‐mode which is able to propagate from high latitudes to the equator. If the amplitude of the unstable L‐mode waves exceed a gamma the concomitant scattering rate of resonant energetic ions should approach the strong diffusion limit. In the absence of significant Landau damping the power spectral density of fluctuating (≳10 Hz) R‐mode electric fields detectable near the equatorial plane by the Voyager plasma wave instrument could then exceed 10 −7 (V/m)²Hz −1 in the inner torus. Such intense ion‐cyclotron waves could account for the observed decrease in ion phase space density and the excitation of auroral emissions on field lines mapping from the Io torus.