EDP Sciences
Free access
Volume 391, Number 1, August III 2002
Page(s) 339 - 351
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20020643

A&A 391, 339-351 (2002)
DOI: 10.1051/0004-6361:20020643

Application of wavelet analysis to transversal coronal loop oscillations

J. Ireland1 and I. De Moortel2

1  L3 Communications Analytics Corporation, NASA Goddard Spaceflight Center, Code 682.3, Building 26, Room G-1, Greenbelt, Maryland 20771, USA
    e-mail: ireland@cdso8.nascom.nasa.gov
2  School of Mathematical and Computational Sciences, University of St. Andrews, St. Andrews, KY16 9SS, Scotland, UK
    e-mail: ineke@mcs.st-and.ac.uk

(Received 24 January 2002 / Accepted 29 April 2002 )

There as yet remain few examples of well observed, transversal oscillations in coronal loops. Such oscillations have the potential to yield much information on the nature of the solar corona, as demonstrated by the analysis of Nakariakov et al. (1999) of a transversely oscillating loop observed in the TRACE 171 Å passband on 14th July, 1998. Their analysis extracts a decaying loop oscillation signal from the data which is then considered in the light of the substantial body of theoretically and computationally derived knowledge of the dynamics of coronal loops. The analysis presented in this paper approaches the reduction of the same dataset using wavelet techniques described by De Moortel & Hood (2000) and De Moortel et al. (2002). The authors show that the value of the decay exponent N in a decaying oscillating time series of the form $\exp(-kt^{N})$ is measurable from a wavelet transform of the time series (for some decay constant k and time t). The application of these techniques shows that the value of the decay exponent in the 14th July, 1998 event is not well determined by the data, i.e., the associated error is very large. Since the value of the decay exponent implies the presence of particular decay mechanisms and not others, the large error associated with the exponent value implies that a wide range of mechanisms should be considered when discussing the physics behind this event. Comments are also made on the time dependence of the oscillation wavelet scale. Two additional examples of transversal coronal loop oscillations are also analysed.

Key words: Sun: activity -- Sun: corona -- Methods: data analysis

Offprint request: J. Ireland, ireland@cdso8.nascom.nasa.gov

© ESO 2002