Comment on "Mode Conversion of Waves In The Ion-Cyclotron Frequency Range in Magnetospheric Plasmas"
Authors: Eun Kim and Jay R. Johnson
Abstract: Recently, Kazakov and Fulop [1] studied
mode conversion (MC) at the ion-ion hybrid
(IIH) resonance in planetary magnetospheric
plasmas by simplifying the dispersion relation
of the fast wave (FW) modes to describe
a cutoff-resonance (CR) pair near the
IIH resonance, which can be reduced to a
Budden problem. They suggested that when
the IIH resonance frequency (ωS) approaches
the crossover frequency (ωcr), and the parallel
wavenumber (k∥) is close to the critical
wavenumber k∗
∥(ωS = ωcr), MC can be
efficient for arbitrary heavy ion density ratios.
In this Comment, we argue that (a)
the FW dispersion relation cannot be simplified
to the CR pair especially near ωcr because
in many parameter regimes there is
a cutoff-resonance-cutoff (CRC) triplet that
completely changes the wave absorption; and
(b) the maximum MC efficiency does not always
occur near k∥ ≈ k∗∥∥.
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Submitted to: Physics Review Letters (February 2013)
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