Jess, D.B., Doorsselaere, T.V., Verth, G. et al. (7 more authors) (2017) An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers. The Astrophysical Journal, 842 (1). ISSN 0004-637X
Abstract
Solar chromospheric observations of sunspot umbrae offer an exceptional view of magneto-hydrodynamic wave phenomena. In recent years, a wealth of wave signatures related to propagating magneto-acoustic modes have been presented, which demonstrate complex spatial and temporal structuring of the wave components. Theoretical modelling has demonstrated how these ubiquitous waves are consistent with an m=0 slow magneto-acoustic mode, which are excited by trapped sub-photospheric acoustic (p-mode) waves. However, the spectrum of umbral waves is broad, suggesting that the observed signatures represent the superposition of numerous frequencies and/or modes. We apply Fourier filtering, in both spatial and temporal domains, to extract chromospheric umbral wave characteristics consistent with an m=1 slow magneto-acoustic mode. This identification has not been described before. Angular frequencies of 0.037 +/- 0.007 rad/s (2.1 +/- 0.4 deg/s), corresponding to a period approximately 170 s for the m=1 mode are uncovered for spatial wavenumbers in the range of 0.45<k<0.90 arcsec^-1 (5000-9000 km). Theoretical dispersion relations are solved, with corresponding eigenfunctions computed, which allows the density perturbations to be investigated and compared with our observations. Such magnetohydrodynamic modelling confirms our interpretation that the identified wave signatures are the first direct observations of an m=1 slow magneto-acoustic mode in the chromospheric umbra of a sunspot.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2017. The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. |
Keywords: | astro-ph.SR; astro-ph.SR |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > School of Mathematics and Statistics (Sheffield) |
Funding Information: | Funder Grant number LEVERHULME TRUST (THE) ECF-2011-331 ROYAL SOCIETY IE141493 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 25 May 2017 13:36 |
Last Modified: | 13 Jul 2017 14:40 |
Published Version: | http://doi.org/10.3847/1538-4357/aa73d6 |
Status: | Published |
Publisher: | American Astronomical Society |
Refereed: | Yes |
Identification Number: | 10.3847/1538-4357/aa73d6 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:116911 |