  To study the dynamics of coronal holes and the role of waves in the
acceleration of the solar wind, spectral observations were performed over polar
coronal hole regions with the SUMER spectrometer on SoHO and the EIS
spectrometer on Hinode. Using these observations, we aim to detect the presence
of propagating waves in the corona and to study their properties. The
observations analysed here consist of SUMER spectra of the Ne VIII 770 A line
(T = 0.6 MK) and EIS slot images in the Fe XII 195 A line (T = 1.3 MK). Using
the wavelet technique, we study line radiance oscillations at different heights
from the limb in the polar coronal hole regions. We detect the presence of long
period oscillations with periods of 10 to 30 min in polar coronal holes. The
oscillations have an amplitude of a few percent in radiance and are not
detectable in line-of-sight velocity. From the time distance maps we find
evidence for propagating velocities from 75 km/s (Ne VIII) to 125 km/s (Fe
XII). These velocities are subsonic and roughly in the same ratio as the
respective sound speeds. We interpret the observed propagating oscillations in
terms of slow magneto-acoustic waves. These waves can be important for the
acceleration of the fast solar wind.

Solar and Stellar Astrophysics