Upper-hybrid resonance or plasma line on magnetospheric passive dynamic spectra? 
Discrimination based on RPI active sounding on IMAGE

R. F. Benson and J. L. Green
NASA/Goddard Space Flight Center

B. W. Reinisch
University of Massachusetts Lowell

The electron density is often derived from an intense emission line on passive 
radio-wave dynamic spectra.  This line, which is either identified as the electron 
plasma frequency fpe or the upper-hybrid frequency fuh, has been attributed to 
electrostatic thermal fluctuations.  The corresponding theory has only been 
developed for the case when fpe >> fce where fce is the electron cyclotron 
frequency.  Under these conditions, appropriate to the solar wind, the intense 
emission corresponds to fpe and is called the plasma line.  In planetary 
magnetospheres, where fpe and fce can be comparable, it is most often attributed to 
fuh (and thus designated as the upper-hybrid resonance line) based on early 
magnetospheric satellite observations.  We here use plasma resonances and wave 
cutoffs stimulated by the Radio Plasma Imager (RPI) on the IMAGE satellite to make 
accurate (within a few %) determinations of fpe and fce in order to relate passive 
RPI dynamic spectral peaks to fpe and fuh as a function of the ambient fpe/fce value.

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To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, CA, Feb. 5-8, 2002.