Coronal hole properties observed with SUMER

We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained on both sides of the boundary of polar coronal holes as well as at other locations along the limb. We compare line intensities, shifts and widths in coronal holes with values obtained in the quiet Sun. We find that with increasing f ormation temperature, spectral lines show an increasingly stronger blueshif t in coronal holes relative to the quiet Sun at an equal heliospheric angle . The width of the lines is generally larger (by a few km/s) inside the cor onal hole. Intensity measurements show the presence of the coronal hole in Ne VIII lines as well as in Fe XII with evidence for a slightly enhanced em ission in polar coronal holes for lines formed below 10(5) K.