Thermal coupling of protons and neutral hydrogen with anisotropic temperatures in the fast solar wind

The thermal coupling between the neutral hydrogen and protons in the inner corona is explored by extending the study of Alien ct al. [1998] to include anisotropic proton temperature to determine what the neutral hydrogen Ly a lpha spectral line measurements reveal about the proton temperature, temper ature anisotropy, and outflow Velocity in the fast solar wind. The anisotro pic proton temperature is produced by ion cyclotron resonant interaction of protons with high-frequency waves, produced by a nonlinear cascade at the Kolmogorov dissipation rate from dominant lower-frequency Alfven waves. As a result of the coupling between the respective parallel and perpendicular components of the neutral hydrogen and proton temperatures, a greater tempe rature anisotropy in the neutral hydrogen develops as compared to the case when the proton temperature is isotropic. The neutral hydrogen and proton e ffective temperatures (T-e (f) (f) ), incorporating: both random and wave m otions of the particles, and outflow velocities: are comparable below simil ar to 3 R-s. Neutral hydrogen and anisotropy ratios, T-H (e f f )/T-paralle l to, similar to 4 below 3 R-s are readily attained, in agreement with obse rvations. Below similar to 3 R-s, these reflect the proton anisotropy ratio . For plasma conditions typical of the fast solar wind, these results imply that the measured Ly alpha spectral line profiles, from which the neutral hydrogen temperature, anisotropy ratio, and outflow velocity are inferred, are equivalent to measurements of protons below similar to 3 R-s. Beyond th is distance the width of the measured Ly alpha spectral lines provides a lo wer limit to the proton effective temperature and temperature anisotropy in the inner corona.