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Astron. Astrophys. 325, 1199-1212 (1997)

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Influence of kink waves in solar magnetic flux tubes on spectral lines

S.R.O. Ploner and S.K. Solanki

Institut für Astronomie, ETH-Zentrum, CH-8092 Zürich, Switzerland

Received 18 November 1996 / Accepted 25 April 1997

Abstract

The kink-mode waves in solar magnetic flux tubes have been proposed as the carriers of significant amounts of energy into the upper atmosphere. Their observational signature, i.e. their influence on polarized spectral lines, is investigated theoretically using a simple MHD model and radiative transfer calculations. The results of a large model grid are presented. The wave is found to periodically shift, broaden, strengthen and change the asymmetry of circularly and linearly polarized profiles (Stokes V and Q, respectively). For most, but not all line parameters it exhibits its largest influence close to the limb. The time fluctuations of all quantities are in phase for Stokes Q and V, except for their amplitudes, which are in antiphase. The signal of the wave in time-averaged profiles depends on the wave frequency. Stokes Q and V exhibit opposite senses of the blue-red asymmetry and wavelength shift. This behaviour is found to be a result of the dependence on frequency of the phase relation between velocity and flux tube inclination. As the wave frequency approaches the cutoff frequency the phase relation changes and the time-averaged line asymmetry and shift decrease rapidly. High frequency kink waves are found to be an extremely efficient source of Stokes Q and V asymmetry, while maintaining a small line shift.

Key words: Sun: magnetic field – Sun: activity – Sun: flux tubes – Stokes radiative transfer – kink waves

Send offprint requests to: S.R.O. Ploner

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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