Solar EUV and UV emission line observations above a polar coronal hole

The roll manoeuvre of SOHO on September 3, 1997 provided the opportunity to study the northern coronal hole with SUMER slits in east-west orientation, so that polar plumes and interplume lanes could be observed simultaneously . A preliminary analysis of the observations shows that lines emitted by io ns with the lowest formation temperatures (with the exceptions of Ne7+ and Ar7+) have the largest ratios of plume to lane radiances at heights between 35 000 km and 70 000 km above the photosphere. All lines have narrower wid ths inside plumes than outside. Electron densities have been deduced in plu mes and lanes from Si VIII and Mg VIII line radiance ratios. The Mg Ix pair was used to determine the corresponding electron temperatures. Neon (with a high first-ionization potential) is found to be less abundant relative to magnesium (with low FIP) in a plume compared to an inter-plume lane, but t he variation is smaller than previously determined Ne/Mg abundance ratios i n a plume relative to the photosphere.