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Magnetoacoustic wave propagation in off-limb polar regions

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dc.contributor.author O'Shea, E
dc.contributor.author Banerjee, D
dc.contributor.author Doyle, J. G
dc.date.accessioned 2007-09-17T10:06:23Z
dc.date.available 2007-09-17T10:06:23Z
dc.date.issued 2006-02
dc.identifier.citation Astronomy & Astrophysics, Vol. 452, No. 3, pp 1059 - 1068 en
dc.identifier.uri http://hdl.handle.net/2248/1797
dc.description.abstract Aims.To find evidence of magnetoacoustic waves in off-limb polar regions. Methods.Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we study oscillations found in radiant flux and velocity measurements from transition region and coronal spectral lines. We use Fourier techniques to measure phase delays between flux ("intensity") oscillations and between velocity oscillations of different transition region-corona and corona-corona line pairs. We also measure the phase delays between flux and velocity oscillations (I-V). Results.The phase delays measured between different line pairs, when plotted over a -180$\degr$ to +180$\degr$ range, line up along diagonal lines corresponding to measurable and fixed time delays. The slopes of these diagonal lines suggest the outward propagation of waves. Using the measured time delays, we estimate propagation speeds for the different line pairs that indicate that the waves producing the observed phase delays are magnetoacoustic waves propagating at speeds close to the sound speed. In addition, we find that the phases occur at fixed integer frequencies of f/4 (90$\degr$) and 3f/16 (67.5$\degr$), instead of the expected interval of f (360$\degr$), indicating that a "Doppler effect" is acting on the waves. Conclusions.From I-V measurements, we find evidence for fast magnetoacoustic waves to be predominantly present at coronal temperatures, while at transition region temperatures slow magnetoacoustic waves are more common. We find strong evidence for outwardly propagating slow magnetoacostic waves in off-limb polar regions and an indication that these propagating waves are influenced by some form of resonant cavity through which they pass. en
dc.format.extent 1907432 bytes
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher EDP Sciences en
dc.relation.uri http://dx.doi.org/10.1051/0004-6361:20053687 en
dc.subject Sun: oscillations en
dc.subject Sun: transition region en
dc.subject Sun: atmosphere en
dc.subject Sun: corona en
dc.title Magnetoacoustic wave propagation in off-limb polar regions en
dc.type Article en

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