An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers
- Astrophysics Research Centre, Queen’s University Belfast, Belfast Northern Ireland, BT7 1NN (United Kingdom)
- Centre for mathematical Plasma Astrophysics Department of Mathematics, KU Leuven, Celestijnenlaan 200B bus 2400, B-3001 Heverlee (Belgium)
- School of Mathematics and Statistics, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH (United Kingdom)
- Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, S1 3JD (United Kingdom)
- Solar Physics and Space Plasma Research Centre (SP2RC), The University of Sheffield, Hicks Building, Hounsfield Road Sheffield, S3 7RH (United Kingdom)
- National Solar Observatory, University of Colorado Boulder, 3665 Discovery Drive, Boulder, CO 80303 (United States)
Solar chromospheric observations of sunspot umbrae offer an exceptional view of magnetohydrodynamic 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 modeling has demonstrated how these ubiquitous waves are consistent with an m = 0 slow magneto-acoustic mode, which is 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{sup −1} (2.1±0.4 deg s{sup −1}, corresponding to a period ≈170 s) for the m = 1 mode are uncovered for spatial wavenumbers in the range of 0.45<0.90 arcsec{sup −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 modeling 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.
- OSTI ID:
- 22872623
- Journal Information:
- Astrophysical Journal, Vol. 842, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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