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

In this work we examine spectral time series of two lines; a transition region line due to 0 V 629Angstrom and the chromospheric line He I 584Angstrom, which were observed simultaneously in a coronal hole with the Coronal Diagnostic Spectrometer (CDS) onboard the SOHO spacecraft. Using wavelet methods, we perform a time series analysis on several small individual regions which allow us to derive the duration as well as the period of the oscillations. The statistical significance of the oscillations was estimated by using a randomisation method. In this short contribution we will present results from one dataset, s18778r00, taken on Maxch 7, 2000. Our observations indicate the presence of compressional waves with periods of 20-30 minutes or longer. These slow magneto-acoustic waves may provide enough energy flux for the acceleration of the fast solar wind.