Bright rings around sunspots

M. P. Rast (), P. A. Fox, H. Lin, B. W. Lites, R. W. Meisner and O. R. White
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M. P. Rast: High Altitude Observatory, National Center for Atmospheric Research
P. A. Fox: High Altitude Observatory, National Center for Atmospheric Research
H. Lin: National Solar Observatory
B. W. Lites: High Altitude Observatory, National Center for Atmospheric Research
R. W. Meisner: High Altitude Observatory, National Center for Atmospheric Research
O. R. White: High Altitude Observatory, National Center for Atmospheric Research

Nature, 1999, vol. 401, issue 6754, 678-679

Abstract: 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.

Date: 1999
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DOI: 10.1038/44343

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