Properties of solar polar coronal hole plasmas observed above the limb

We determine the line-of-sight emission measure distribution and nonthermal motions as a function of height above the limb in the north and south pola r coronal holes. These quantities are derived from extreme-ultraviolet (EUV ) spectra obtained from the Solar Ultraviolet Measurements of Emitted Radia tion (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The SUMER slit was oriented along the north-south direction for all the observations, and the spatial resolution is about 1 ". The spectra were obtained from a number of different types of observations in 1996. We select a group of emission lines for analysis for which, under the usual a ssumption of ionization equilibrium, the maximum emissivities span the temp erature range from about 3 x 10(5) K up to about 1.1 x 10(6) K. We compare our results with recently published similar observations of a west limb qui et-Sun streamer region, with other coronal hole results based on SUMER spec tra, and with earlier observations of the quiet Sun and coronal holes obtai ned from Skylab and rocket spectra. We find that the electron temperature i n the polar holes increases with height above the limb, that the emission m easure distribution of plasma located at line-of-sight heights less than ab out 60 " peaks at a temperature of about 9 x 10(5) K, and that nonthermal m otions sometimes, but not always, increase slightly with height above the l imb. When observed, these increases level off above the limb at about 120 " . We speculate that the increases with height above the limb may be a manif estation of the fast solar wind. They may also be due to the reduction in t ransition region structures with increasing limb height. We also discuss wa ve heating as a cause of the line width increases.