UVCS/SOHO Observations of H I Lyman Alpha Line Profiles in Coronal Holes at Heliocentric Heights Above 3.0 R⊙
Cranmer, S. R.; Ciaravella, A.; Noci, G.; Kohl, J. L.; Panasyuk, A. V.; Gardner, L. D.; Smith, P. L.; Suleiman, R. M.; Frazin, R.; Hauck, R.
United States, Italy
Abstract
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) has been used to measure spectral line profiles for H I Lyα in the south polar coronal hole at projected heliocentric heights from 3.5 to 6.0 R⊙ during 1998 January 5 11. Observations from 1.5 to 2.5 R⊙ were made for comparison. The H I Lyα profile is the only one observable with UVCS above 3.5 R⊙ in coronal holes. Within this region the outflowing coronal plasma becomes nearly collisionless and the ionization balance is believed to become frozen.