Dispersion Characteristics for Plasma Resonances of Maxwellian and Kappa
Distribution Plasmas and their Comparisons to the IMAGE/RPI Observations

Adolfo F.-Vinas, R. F. Benson, and R. L. Mace 


The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora
Global Exploration (IMAGE) satellite stimulates short-range plasma wave
echoes and plasma emissions, known as plasma resonances, detected on
plasmagrams. These resonances are used to provide measurements of the local
electron density ne and magnetic field strength |B|. The RPI-stimulated
resonances are the magnetospheric analog of plasma resonances stimulated by
topside ionospheric sounders. These resonances are stimulated at the
harmonic of the electron cyclotron frequency fce, the electron plasma
frequency fpe and the upper-hybrid frequency fuh (where fuh2 = fpe2 + fce2).
They are also observed between the harmonics of fce (i.e. n fce) both above
and below fpe, and are known as the Qn and Dn resonances, respectively. In
this work we solely focus on the Qn resonances. Calculations of these
resonances in the ionospheric environment, based upon a thermal Maxwellian
plasma model provided confidence in the resonance identification. There is
an apparent difference however, between the observed Qn resonances and
calculations based on a Maxwellian plasma model in the magnetosphere
environment. For example, the QnÕs are often (and perhaps consistently)
observed at frequencies slightly lower than expected for a Maxwellian
plasma. We present a new set of resonance calculations based upon the
non-thermal kappa distribution that provides dispersion characteristics of
these resonances. Comparisons of these calculations to the IMAGE/RPI
observations seems to resolve the frequency discrepancy. The results also
provide insight into the nature of the electron distribution function in 
the magnetosphere.

_______________
Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004