UVCS/SOHO Observations of H I Lyman Alpha Line Profiles in Coronal Holes at Heliocentric Heights Above 3.0 Solar Radius

摘要

The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) has been used to measure spectral line profiles for H I Ly#alpha# in the south polar coronal hole at projected heliocentric heights from 3.5 to 6.0 solar radius during 1998 January 5-11. Observations from 1.5 to 2.5 solar radius were made for comparison. The H I Ly#alpha# profile is the only one observable with UVCS above 3.5 solar radius in coronal holes. Within this region the outflowing coronal plasma becomes nearly collisionless and the ionization balance is believed to become frozen. In this paper, the 1/e half widths of the coronal velocity distributions are provided for the observed heights. The velocity distributions include all motions contributing to the velocities along the line of sight (LOS). The observations have been corrected for instrumental effects and interplanetary H I Ly#alpha#. The half widths were found to increase with projected heliographic height from 1.5 to 2.5 solar radius and decrease with height from 3.5 to 5 solar radius.