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Astronomy & Astrophysics manuscript no. (will be inserted by hand later)

Summary: Astronomy & Astrophysics manuscript no.
(will be inserted by hand later)
On the theory of MAG waves and a comparison with sunspot
observations from CDS/SoHO
D. Banerjee 1 , E. O'Shea 2 , M. Goossens 1 , J.G.Doyle 3 , and S. Poedts 1
1 Centre for Plasma Astrophysics, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001, Leuven, Belgium
2 Instituto de Astro sica de Canarias, C/ V  ia Lactea s/n, 38200 La Laguna, Tenerife, The Canary Islands, Spain
3 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
Received date, accepted date
Abstract. We examine the in uence of non-adiabatic e ects on the modes of an isothermal strati ed magnetic
atmosphere. We present new solutions for magneto-acoustic-gravity(or mag) waves in the presence of a radiative
heat exchange based on Newton's law of cooling. An analytic expression for the dispersion relation is derived,
which allows the e ect of a weak magnetic eld on the modes to be studied. The insight so gained proves useful
in extending the computations to the moderate{high eld case. In the second part we present observations of
two sunspots obtained in the euv wavelength range with the Coronal Diagnostic Spectrometer (cds) on SoHO.
We examine the time series for the line intensities and relative velocities and calculate their power spectra using
wavelet transforms. We nd oscillations in the chromosphere and transition region above the sunspots in the
temperature range log T = 4.6-5.4 K. Most of the spectral power above the umbra is contained in the 5-7 mHz
frequency range. When the cds slit crosses the sunspot umbra a clear 3 min oscillation is observed. The observed
oscillation frequencies are compared with the computed frequencies and the observations are interpreted in terms


Source: Armagh Observatory


Collections: Physics