Coronal oscillations in the vicinity of a sunspot as observed by GIS/CDS

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland e-mail: chl@arm.ac.uk
² Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
³ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK

Received: 11 October 2004
Accepted: 5 January 2005

Abstract

In this paper, we present results from a time series analysis of data from the Grazing Incidence Spectrometer (GIS), onboard SoHO. Our observations were concentrated at the boundary between the quiet Sun and an active region, close to a sunspot plume. The dominant oscillations in all the lines studied are of periods longer than 5 min. Although our observations were not taken directly above the sunspot, the 3-min oscillations, which are normally associated with the umbra, are seen in several spectral lines, suggesting some leakage perhaps via plume structures. The oscillations of coronal lines form wavepackets, and are intermittent with no obvious decay. The average time scale of the intermittence is of the order of 20 min, which would correspond to a source size of 2 arcsec.