Back to Volume
Paper: The Impact of UVCS/SOHO Observations on Models of Ion-Cyclotron Resonance Heating of the Solar Corona
Volume: 154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop
Page: 592
Authors: Cranmer, Steven R.; Field, George B.; Kohl, John L.
Abstract: We examine the compatibility between theoretical models and observations of the temperatures and anisotropic velocity distributions of hydrogen and minor ions in the solar corona. The UVCS instrument on board SOHO has measured hydrogen kinetic temperatures along lines of sight in coronal holes in excess of 3 x 106 K, and O^{+5} ion kinetic temperatures of at least 2 x 108 K. In addition, the velocity distributions in the radial direction (mainly perpendicular to the line of sight) are smaller, possibly implying temperature anisotropies of order Tperp / Tparallel ~ 100 for the oxygen ions. These properties can be understood only in terms of a mechanism which heats and/or accelerates heavier ions more than lighter ones (possibly proportionally to mionalpha, where alpha >~ 1), and preferentially in directions perpendicular to the magnetic field. We examine various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfven waves, which may be the most natural physical mechanism to produce such plasma conditions. We show that a quantitative model should predict the spectrum of waves required to reproduce the observations.
Back to Volume