The physical conditions in a polar coronal hole and nearby regions from Norikura and SOHO observations

The distribution of emission-line intensities, Doppler velocities, and line widths in a polar coronal hole and nearby regions are obtained from the sp ectroscopic observations carried out on 1998 November 3 at the Norikura Sol ar Observatory, Japan. The coronal red line [Fe x] lambda 6374 that is prom inent at coronal hole temperatures is used for the study. The coronal image s in Fe nr and Fe x 171 Angstrom and Fe XII 195 A from the Extreme-Ultravio let Imaging Telescope (EIT) on the Solar and Heliospheric Obsevatory (SOHO) are used to get the temperature map of the corona at the time of observati on. Combining both, we have obtained the nonthermal velocities in the regio n without the usual assumption of a uniform ion temperature. Several plume structures are identified within the coronal hole, and it is found that lin e widths are smaller in plumes than in the interplume regions, which is als o reported from recent SOHO observations. The line-of-sight Doppler velocit ies in the coronal hole are larger than those in the quiet region, probably because of the excess outflow in the coronal hole. A rough negative correl ation between intensity and Doppler velocity, similar to that between inten sity and line width, is observed in the coronal hole. The typical nontherma l velocity in coronal holes is 24 km s(-1) while that in quiet regions is 1 5 km s(-1). The enhanced nonthermal velocity in the coronal hole is suggest ive of the important role of the nonthermal broadening mechanism in the acc eleration of fast solar wind. Also, the nonthermal velocities are larger (u p to 27%) at the interplume regions as compared to plumes. The findings gen erally support the prevailing view that the interplume regions are the sour ce regions of the fast solar wind.