Comment on Khazanov et al. [2002] and Khazanov et al. [2006]

摘要

[1] Electromagnetic ion cyclotron (EMIC) waves are an important magnetospheric emission, which strongly affects the dynamics of resonant radiation belt particles, leading to either nonadiabatic heating or pitch-angle scattering and loss to the atmosphere. EMIC waves are excited near the magnetic equator in bands below the proton gyrofrequency. The source of free energy for wave growth is provided by natural gradients in the phase space density of ring current ions, which develop during inward convection from the plasmasheet [e.g., Jordanova, 2005]. Waves are preferentially excited with wave normals aligned with the ambient magnetic field, but during unducted propagation in the heterogeneous magnetosphere the wave normal tends to become highly oblique, and the waves are subsequently subject to severe Landau damping by thermal electrons [Cornwall et al., 1971; Thorne and Horne, 1992]. During propagation away from the equatorial source region, EMIC waves also move into spatial regions where their frequency becomes comparable to the gyrofrequency (or multiples thereof) of heavy ions (such as He+ or O+). At such locations, the EMIC wave energy can suffer significant cyclotron resonant damping by the thermal heavy ion population [Horne and Thorne, 1990, 1997; Thorne and Horne, 1993, 1994].