An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers

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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 (2.1 ± 0.4 deg/s, corresponding to a period ~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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      • An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers

        Rights statement: © 2017 The Authors. This is an open access article published under a Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

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      DOI

      Original languageEnglish
      Article number59
      Number of pages9
      JournalThe Astrophysical Journal
      Journal publication date10 Jun 2017
      Issue number1
      Volume842
      DOIs
      StatePublished - 10 Jun 2017

        Research areas

      • Sun: chromosphere, Sun: magnetic fields, Sun: oscillations, Sun: photosphere, sunspots

      ID: 130795944