Inferring Magnetospheric Heavy Ion Density Using EMIC Waves
Authors: Eun-Hwa Kim, Jay R. Johnson, Hyomin Kim and Dong-Hun Lee
Abstract: We present a method to infer heavy ion concentration
ratios from EMIC wave observations that result from ionion
hybrid (IIH) resonance. A key feature of the ion-ion
hybrid resonance is the concentration of wave energy in a
field-aligned resonant mode that exhibits linear polarization.
This mode converted wave is localized at the location where
the frequency of a compressional wave driver matches the
IIH resonance condition, which depends sensitively on the
heavy ion concentration. This dependence makes it possible
to estimate the heavy ion concentration ratio. In this
letter, we evaluate the absorption coefficients at the IIH
resonance at Earth's geosynchronous orbit for variable concentrations
of He+ and field-aligned wave numbers using a
dipole magnetic field. Although wave absorption occurs for
a wide range of heavy ion concentrations, it only occurs for
a limited range of field-aligned wave numbers such that the
IIH resonance frequency is close to, but not exactly the same
as the crossover frequency. Using the wave absorption and
observed EMIC waves from GOES-12 satellite, we demonstrate
how this technique can be used to estimate that the
He+ concentration is around 4% near L = 6.6.
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PPPL Report is pending