Long-period oscillations in polar plumes as observed by CDS on SOHO

We examine spectral time series of the transition region line O v 629 Angst rom, observed with the Coronal Diagnostic Spectrometer (CDS) on the SOHO sp acecraft in July 1997. Both Fourier and wavelet transforms have been applie d independently to the analysis of plume oscillations in order to find the most reliable periods. The wavelet analysis allows us to derive the duratio n as well as the periods of the oscillations. Our observations indicate the presence of compressional waves with periods of 10-25 min. We have also de tected a 11 +/-1 min periodicity in the network regions of the north polar coronal hole. The waves are produced in short bursts with coherence times o f about 30 min. We interpret these oscillations as outward propagating slow magneto-acoustic waves, which may contribute significantly to the heating of the lower corona by compressive dissipation and which may also provide e nough energy flux for the acceleration of the fast solar wind. The data sup port the idea that the same driver is responsible for the network and plume oscillations with the network providing the magnetic channel through which the waves propagate upwards from the lower atmosphere to the plumes.