Test for Alfven Wave Signatures in a Solar Coronal Hole

Abstract

Using spectral line observations to study minor ion motions in a solar coronal hole, a test was made for the presence of Alfven waves. From this we conclude that the Alfven wave flux into the upper portion of the hole is not significant. The SOHO/SUMER ultraviolet spectrograph was used to observe 22 coronal ions with masses ranging from 14mH to 56mH and charge states ranging from +4 to +11. The line widths of 33 vacuum ultraviolet (VUV) lines radiated by these ions were measured off-limb in a coronal hole at heights between 1.02 and 1.3 solar radii (R☉), and the height dependencies of sufficiently intense lines were measured to test for the increase of width with height expected for undamped Alfven wave propagation. Line widths from ions formed at coronal hole temperatures were found to increase with height to 1.1 R☉ and were constant for greater heights. If this line broadening is a manifestation of Alfven wave propagation, the waves are strongly damped above 1.1 R☉. Consequently, another mechanism must transport energy to the solar wind acceleration region. In addition, the observed dependence of line-of-sight ion speed squared on the reciprocal of the mass indicates that there is not a common nonthermal velocity if there is a common ion temperature. This suggests that Alfven waves do not cause the anomalously large effective temperatures measured.