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 ω_Re,H~=(2.3-2.4)Ω_⁴He, which corresponds to ~(3.68-3.84)Ω_O⁺⁵ or ~(3.10-3.24)Ω_Mg⁺⁹, and thus can heat O⁺⁵ through the fourth harmonic resonance and Mg⁺⁹ through the third harmonic resonance. Here Ω_σ is the cyclotron frequency of particle species σ. The H-cyclotron waves are efficient at heating O⁺⁵ if ω_Re,H~=2.4Ω_⁴He and Mg⁺⁹ if ω_Re,H~=2.3Ω_⁴He. 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.