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Cut-off period for slow magnetoacoustic waves in coronal plasma structures
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Afanasyev, A. N. and Nakariakov, V. M. (Valery M.) (2015) Cut-off period for slow magnetoacoustic waves in coronal plasma structures. Astronomy & Astrophysics, 582 . A57. doi:10.1051/0004-6361/201526530 ISSN 0004-6361.
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WRAP_9877890-px-140416-tube_cutoff-1.pdf - Accepted Version - Requires a PDF viewer. Download (437Kb) | Preview |
Official URL: http://dx.doi.org/10.1051/0004-6361/201526530
Abstract
Context. There is abundant observational evidence of longitudinal compressive waves in plasma structures of the solar corona, which are confidently interpreted in terms of slow magnetoacoustic waves. The uses of coronal slow waves in plasma diagnostics, as well as analysis of their possible contribution to coronal heating and the solar wind acceleration, require detailed theoretical modelling.
Aims. We investigate the effects of obliqueness, magnetic field, and non-uniformity of the medium on the evolution of long-wavelength slow magnetoacoustic waves guided by field-aligned plasma non-uniformities, also called tube waves. Special attention is paid to the cut-off effect due to the gravity stratification of the coronal plasma.
Methods. We study the behaviour of linear tube waves in a vertical untwisted straight field-aligned isothermal plasma cylinder. We apply the thin flux tube approximation, taking into account effects of stratification caused by gravity. The dispersion due to the finite radius of the flux tube is neglected. We analyse the behaviour of the cut-off period for an exponentially divergent magnetic flux tube filled in with a stratified plasma. The results obtained are compared with the known cases of the constant Alfven speed and the pure acoustic wave.
Results. We derive the wave equation for tube waves and reduce it to the form of the Klein–Gordon equation with varying coefficients, which explicitly contains the cut-off frequency. The cut-off period is found to vary with height, decreasing significantly in the low-beta plasma and in the plasma with the beta of the order of unity. The depressions in the cut-off period profiles can affect the propagation of longitudinal waves along coronal plasma structures towards the higher corona and can form coronal resonators.
| Item Type: | Journal Article | ||||||||
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| Subjects: | Q Science > QB Astronomy | ||||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||
| Library of Congress Subject Headings (LCSH): | Sun -- Corona, Magnetohydrodynamics, Solar activity, Solar magnetic fields, Astrophysics | ||||||||
| Journal or Publication Title: | Astronomy & Astrophysics | ||||||||
| Publisher: | EDP Sciences | ||||||||
| ISSN: | 0004-6361 | ||||||||
| Official Date: | 7 October 2015 | ||||||||
| Dates: |
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| Volume: | 582 | ||||||||
| Article Number: | A57 | ||||||||
| DOI: | 10.1051/0004-6361/201526530 | ||||||||
| Status: | Peer Reviewed | ||||||||
| Publication Status: | Published | ||||||||
| Date of first compliant deposit: | 22 April 2016 | ||||||||
| Date of first compliant Open Access: | 22 April 2016 | ||||||||
| Funder: | Russian Foundation for Basic Research (RFBR), European Research Council (ERC), Science and Technology Facilities Council (STFC) | ||||||||
| Grant number: | 15–32–20504 mol_a_ved, 15–02–01077, ST/L000733/1 |
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