Abstract
Using a magnetograph, we examine four sunspots for evidence of a magnetic canopy at the penumbra/photosphere boundary. The penumbral edge is determined from the photometric intensity and is defined to correspond to the value of the average intensity minus twice the standard deviation from the average. From a comparison of the location of this boundary with the location of contours of the vertical and horizontal components of the magnetic field, we conclude that the data are best represented by canopy-type fields close to all four sunspots. There is some evidence that the magnetic inclination in the canopies is 5°–15° with respect to the horizontal and that the canopy base height lies in the middle/upper photosphere. The observations further suggest that the magnetic canopy of a sunspot begins at its outer penumbral boundary.
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Adams, M., Solanki, S.K., Hagyard, M. et al. A search for sunspot canopies using a vector magnetograph. Sol Phys 148, 201–218 (1993). https://doi.org/10.1007/BF00645086
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DOI: https://doi.org/10.1007/BF00645086