Kazue Takahashi, Space Physics Group (SRP), The Johns Hopkins University Applied Physics Laboratory
Title: "Externally Driven Plasmaspheric ULF Waves Observed by the Van Allen
Abstract: The Van Allen Probes, with their low-inclination elliptical orbits with
apogee at 5.8 Re, are ideal for studying ULF waves in the plasmasphere. We
analyze data acquired by these spacecraft on 8 November 2012 to gain new
insight into quiet-time ULF waves in the plasmasphere. The waves exhibit
strong spectral power in the 5-40 mHz band outside L = 3 and include
muliharmonic toroidal waves visible up to the 11th harmonic, which is
unprecedented in the plasmasphere. During this wave activity, the IMF cone
angle was small, suggesting that the plasmaspheric waves were driven by
broadband compressional ULF waves originating in the foreshock region.
This scenario is supported by the tailward propagation of the
compressional magnetic field perturbations that is determined using
two-spacecraft phase delay analysis. The phase delay analysis, when
applied to the azimuthal component of the magnetic field, also reveals
signatures of field line resonance that have not been reported in space.
Finally, using the observed toroidal wave frequencies, we estimate the
plasma mass density for 2.4-5.8. By comparing the mass density with the
electron number density that is estimated from the spectrum of plasma
waves, we find that the ion composition is dominated by H+.
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