A&A 387, L13-L16 (2002)
DOI: 10.1051/0004-6361:20020436

Letter

The detection of 3 & 5 min period oscillations in coronal loops

I. De Moortel¹, J. Ireland², A. W. Hood¹ and R. W. Walsh<sup>3

1</sup>  School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland
²  L3Com Analytics Corp., NASA GSFC, Code 682.3, Bldg. 26, Greenbelt, MD 20771, USA
³  Department of Physics, Astronomy and Maths, University of Central Lancashire, Preston, PR1 2HE, UK

(Received 8 March 2002 / Accepted 21 March 2002)

Abstract
High cadence, 171 Å, TRACE observations show that outward propagating intensity disturbances are a common feature in large, quiescent coronal loops. These oscillations are interpreted as propagating slow magneto-acoustic waves. Using a wavelet analysis, we found periods of the order of  s. However, a careful study of the location of the footpoints revealed a distinct separation between those loops that support oscillations with periods smaller than 200 s and periods larger than 200 s. It was found that loops that are situated above sunspot regions display intensity oscillations with a period of the order of  s, whereas oscillations in "non-sunspot" loops show periods of the order of  s. We conclude that the observed longitudinal oscillations are not flare-driven but are most likely caused by an underlying driver exciting the loop footpoints. This result suggests that the underlying oscillations can propagate through the transition region and into the corona.

Key words: MHD -- Sun: oscillations -- corona -- sunspots

Offprint request: I. De Moortel, ineke@mcs.st-and.ac.uk

© ESO 2002

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