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Astronomy & Astrophysics manuscript no. eos5592 c ESO 2006 October 2, 2006

Summary: Astronomy & Astrophysics manuscript no. eos5592 c ESO 2006
October 2, 2006
A statistical study of wave propagation in coronal holes
E. O'Shea1, D. Banerjee2, and J.G.Doyle1
Armagh Observatory, College Hill, Armagh BT61 9DG, N.Ireland
e-mail: eos@arm.ac.uk, e-mail: jgd@arm.ac.uk
Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560 034, India
e-mail: dipu@iiap.res.in
Aims. To find evidence for propagating magnetoacoustic waves in equatorial and polar coronal hole locations
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 (O V 629) and coronal lines (Mg X 624, Si XII 520). We use Fourier techniques to measure
phase delays between flux (`intensity') oscillations and between velocity oscillations of different transition region­corona and corona­corona
line pairs. We also measure the phase delays between flux and velocity oscillations (I­V) in the three spectral lines investigated.
Results. We find outwardly propagating slow magnetoacoustic waves in both of the coronal hole regions studied. The propagation speeds are
found to be lower than those found in off-limb locations. We find evidence for a resonant cavity or `Doppler' effect, whereby the measured
phases are present at fixed integer intervals of f/4 (90
of phase) and 3f/8 (135


Source: Armagh Observatory


Collections: Physics