Measurements of outflow from the base of solar coronal holes

New evidence is presented that EUV emission lines formed at the levels of the base of the corona and the transition region are systematically shifted to shorter wavelengths within coronal holes relative to the rest of the solar disk, and that moreover this shift increases with height in the atmosphere. This evidence is contained in measurements made with a rocket-borne EUV spectrometer having high spectroscopic resolution and stability flown on 1980 July 15. Repeated measurements were made along a chord of the solar disk that crossed a compact coronal hole near Sun center identified on lambda10830 He I spectroheliograms. The maximum measured shift corresponded to a velocity of 12 km s-1 in lambda625 Mg x (Tapprox.10/sup 6.15/ K) and 7 km s-1 in lambda629 O V (Tapprox.10/sup 5.40/ K). If these velocities correspond to a true mass flux, they provide important data on the acceleration of coronal plasma in open magnetic field regions. But whether or not these observed Doppler displacements measure a true systematic flow, they are certainly a strong and significant signature of coronal holes, now measured on three rocket flights. The combined evidence for this is reviewed and the implications considered