UVCS/SOHO observations of spectral line profiles in polar coronal holes

Ultraviolet emission line profiles have been measured on 15-29 September 19 97 for H I 1216 Angstrom, O VI 1032, 1037 Angstrom and Mg X 625 Angstrom in a polar coronal hole, at heliographic heights rho (in solar radii) between 1.34 and 2.0. Observations of H I 1216 Angstrom and the O VI doublet from January 1997 for rho = 1.5 to 3.0 are provided for comparison. Mg X 625 Ang strom is observed to have a narrow component at rho = 1.34 which accounts f or only a small fraction of the observed spectral radiance, and a broad com ponent that exists at all observed heights. The widths of O VI broad compon ents are only slightly larger than those for H I at rho = 1.34, but are sig nificantly larger at rho = 1.5 and much larger for rho > 1.75. In contrast, the Mg X values are less than those of H I up to 1.75 and then increase ra pidly up to at least rho = 2.0, but never reach the values of O VI.