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Bright rings around sunspots

Nature volume 401, pages 678–679 (1999)Cite this article

Abstract

There are two possible explanations for why sunspots are dark: the partial suppression by the sunspot magnetic fields of convective energy transport from the underlying layers1, or the removal of energy from the sunspot by enhanced hydromagnetic wave radiation2. Both processes would reduce the energy emitted radiatively. The first explanation is currently favoured3, and predicts that the blocked energy should show up as a bright ring around the spot2, with the actual brightness of the ring sensitive to details of solar convective transport and sunspot structure4. Previous searches5 for these bright rings were inconclusive because of the presence of bright, vertical magnetic flux tubes near the spots, and a lack of sufficient precision in the observations. Here we report high-photometric-precision observations of bright rings around eight sunspots. The rings are about 10 K warmer than the surrounding photosphere and extend at least one sunspot radius out from the penumbra. About 10% of the radiative energy missing from the sunspots is emitted through the bright rings. We also report observations of a second set of sunspots, for which simultaneous magnetic field measurements demonstrate that the rings are not associated with vertical flux tubes.

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Figure 1: Bright rings are seen in all wavelength bands measured.
Figure 2: Ring temperature enhancements are of the order of 10 K and scale with sunspot size.
Figure 3: The enhanced brightness in the ring originates mainly in regions of very weak magnetic field.

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Acknowledgements

We thank J. Kuhn, K. MacGregor, C. Rice, P. Seagraves, A. Skumanich, K. Streader and M. Woodard. The National Center for Atmospheric Research and the National Solar Observatory are sponsored by the National Science Foundation.

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Authors and Affiliations

  1. High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder, 80307, Colorado, USA

    M. P. Rast, P. A. Fox, B. W. Lites, R. W. Meisner & O. R. White

  2. National Solar Observatory, Sunspot, 88349, New Mexico, USA

    H. Lin

Authors
  1. M. P. Rast
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  2. P. A. Fox
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  3. H. Lin
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  4. B. W. Lites
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  5. R. W. Meisner
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  6. O. R. White
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Correspondence to M. P. Rast.

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Rast, M., Fox, P., Lin, H. et al. Bright rings around sunspots. Nature 401, 678–679 (1999). https://doi.org/10.1038/44343

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