Three-Fluid 2.5-dimensional Magnetohydrodynamic Model of the Effective Temperature in Coronal Holes

Abstract

Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations show that protons and minor ions are hot (T_p>10⁶ K, T_i>10⁷ K) and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfvénic fluctuations in the solar wind. Using the three-fluid 2.5-dimensional MHD model, we have shown that the unresolved Alfvénic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. However, Alfvén waves with realistic amplitudes cannot reproduce the O⁵⁺ perpendicular temperature and anisotropy deduced from UVCS observations. This suggests that the minor ions are heated by a different mechanism than protons.