Journal
ASTROPHYSICAL JOURNAL
Volume 842, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/1538-4357/aa73d6
Keywords
Sun: chromosphere; Sun: magnetic fields; Sun: oscillations; Sun: photosphere; sunspots
Categories
Funding
- UK Science and Technology Facilities Council (STFC)
- Randox Laboratories Ltd. [059RDEN-1]
- Odysseus grant of the FWO Vlaanderen
- Belspo [IAP P7/08 CHARM]
- KU Leuven [GOA-2015-014]
- Chinese Academy of Sciences President's International Fellowship Initiative [2016VMA045]
- Royal Society (UK)
- Leverhulme Trust
- CSUN
- Invest NI
- Science and Technology Facilities Council [ST/M000826/1, ST/J001430/1] Funding Source: researchfish
- STFC [ST/J001430/1, ST/L002744/1, ST/M000826/1, ST/P000304/1, ST/K004220/1] Funding Source: UKRI
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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(-1) (2.1 +/- 0.4 deg s(-1), corresponding to a period approximate to 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 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.
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