Preferential Heating of Particles by H-Cyclotron Waves Generated by a Global Magnetohydrodynamic Mode in Solar Coronal Holes

Abstract

Preferential heating of particles by H-cyclotron waves is investigated to explain the recent measurements of anisotropic heating of ions in solar coronal holes. First, the dispersion relation of H-cyclotron waves generated by a global MHD mode in the solar coronal hole is numerically studied. Then, heating of H, O+5, and Mg+9 due to the resonant and nonresonant dissipations of H-cyclotron waves is quantitatively studied. It is shown that H-cyclotron waves can be excited at a frequency ωRe, H ≃ (2.3-2.4)Ω, which corresponds to ~(3.68-3.84)Ω or ~(3.10-3.24)Ω, and thus can heat O+5 through the fourth harmonic resonance and Mg+9 through the third harmonic resonance. Here Ωσ is the cyclotron frequency of particle species σ. The H-cyclotron waves are efficient at heating O+5 if ωRe, H ≃ 2.4Ω and Mg+9 if ωRe, H ≃ 2.3Ω. Protons can only be weakly heated by the H-cyclotron waves through the nonresonant dissipation. The amount of heating for H, O+5, and Mg+9 can reach the order of measurements. Furthermore, the harmonic resonances of O and Mg with other charge states and of other heavy ions with proper charge states are discussed.