Long Period Oscillations in Polar Plumes as Observed by CDS on SoHO

Abstract

We examine time series of the transition region spectral line O v 629 Å, observed with the Coronal Diagnostic Spectrometer (CDS) onboard the SoHO spacecraft. Primarily we were looking for intensity and velocity oscillations in polar plumes, however by chance we detected a giant macro-spicule at the limb and were able to follow its dynamical structure. We have reported the dynamics of the giant macro-spicule in Banerjee et al. (2000a) and have also reported the existence of long period oscillations in the polar plumes as observed in the O v 629 Å line in Banerjee et al. (2000a,b). In this short contribution we revisit one of these dataset, namely s16834r01 to test the reliability of the observed periods. The statistical significance of the oscillations is estimated by using a randomisation method. Our analysis re-confirms the presence of compressional waves with periods of 20-25 minutes.