Issue |
A&A
Volume 526, February 2011
|
|
---|---|---|
Article Number | A80 | |
Number of page(s) | 4 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361/201016063 | |
Published online | 24 December 2010 |
Nonlinear long-wavelength torsional Alfvén waves
1
Centre for Fusion, Space and Astrophysics, Physics DepartmentUniversity of
Warwick, Coventry
CV4 7AL, UK
e-mail: s.vasheghani-farahani@warwick.ac.uk
2
Central Astronomical Observatory of the Russian Academy of
Sciences at Pulkovo, 196140
St Petersburg,
Russia
3
Centrum voor Plasma-Astrofysica, Mathematics
Department, Celestijnenlaan 200B
bus 2400, 3001
Leuven,
Belgium
Received:
3
November
2010
Accepted:
23
November
2010
Aims. We investigate the nonlinear phenomena accompanying long-wavelength torsional waves in solar and stellar coronae.
Methods. The second order thin flux-tube approximation is used to determine perturbations of a straight untwisted and non-rotating magnetic flux-tube, nonlinearly induced by long-wavelength axisymmetric magnetohydrodynamic waves of small, but finite amplitude.
Results. Propagating torsional waves induce compressible perturbations oscillating with double the frequency of the torsional waves. In contrast with plane shear Alfvén waves, the amplitude of compressible perturbations is independent of the plasma-β and is proportional to the torsional wave amplitude squared. Standing torsional waves induce compressible perturbations of two kinds, that grow with the characteristic time inversely proportional to the sound speed, and that oscillate at double the frequency of the inducing torsional wave. The growing density perturbation saturates at the level, inversely proportional to the sound speed.
Key words: magnetohydrodynamics (MHD) / waves / Sun: corona / Sun: activity / magnetic fields
© ESO, 2010
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