Comment on 'Mode Conversion of Waves in the Ion-Cyclotron Frequency Range in Magnetospheric Plasmas'

摘要

Recently, Kazakov and Fueloep 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 (ω_S) approaches the crossover frequency (ω_(cr)), and the parallel wave number (k_‖) is close to the critical wave number k_‖~* ≡ (ω/c)[ε_S(ω=ω_(cr))]~(1/2), 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 ω_(cr) 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 ω_S≈ω_(cr).