Magnetospheric electron densities inferred from upper-hybrid band emissions

R. F. Benson, P. A. Webb, J. L. Green, L. Garcia, B. W. Reinisch


The magnetospheric electron density Ne can often be obtained to within a few
percent from passive radio-wave dynamic spectra when the electron plasma
frequency fpe (~Ne^1/2) is greater than the electron cyclotron frequency fce.
This conclusion is based on interleaved active and passive observations from the
Radio Plasma Imager (RPI) on the IMAGE satellite in the vicinity of the
plasmapause. The Ne determinations are based on the frequency limits of an
intense narrowband emission identified as the upper-hybrid band. The lower limit
is identified with fpe and the upper limit with the upper-hybrid frequency fuh =
(fpe^2 + fce^2)^1/2. These frequency limits and the large amplitude of the
emission, typically 20 dB or more above background, suggest strong Z-mode waves,
rather than quasi-thermal fluctuations, as the emission source.

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Geophysical Research Letters, 31, L20803, doi:10.1029/2004GL020847, 2004