Astron. Astrophys. 325, 1199-1212
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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
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
© European Southern Observatory (ESO) 1997
Online publication: September 9, 1997
Last change: April 28, 1998