Long period oscillations in the inter-plume regions of the Sun

Abstract

We examine long spectral time series of inter-plume lanes observed on the 14th and 15th March 2000 with the Coronal Diagnostic Spectrometer (CDS) on-board SoHO. The observations were obtained in lines over a wide temperature range, from the chromosphere to the corona. The statistical significance of the oscillations was estimated by using a randomisation method. Our observations indicate the presence of compressional waves with periods of 20-50 min or longer, both off-limb and on-disk and up to 70 min further out to at least 25 arcsec off-limb. To our knowledge this is the first time that long period oscillations in the inter-plume regions close to the limb of the Sun have been detected. 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 some of the enough energy flux required for the acceleration of the fast solar wind. These slow waves may have been produced at the network boundaries in the coronal hole.