Are sunspot penumbrae deep or shallow?

Details Are sunspot penumbrae deep or shallow? Are sunspot penumbrae deep or shallow?

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...267..287s&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 267, no. 1, p. 287-291.

Astronomy and Astrophysics

Astrophysics

52

Penumbras, Solar Magnetic Field, Sunspots, Magnetic Flux, Solar Activity

Scientific paper

From the strength and inclination of the magnetic field measured across large symmetric sunspots, we estimate the fraction of the total magnetic flux of the sunspot passing through the solar surface in the penumbra. It is found that on average approximately 1/2-2/3 of the total magnetic flux of the spot emerges in its penumbra. Sunspot penumbrae are therefore deep, i.e. the tau = 1 level does not correspond to the lower magnetic boundary of the spot in its penumbra (except perhaps near its outer edge). Furthermore, the analyzed data do not support the passage of any significant amount of magnetic flux through the solar surface (in either direction) at or beyond the edge of the sunspot. The observations support models of the sunspot magnetic field which are bounded by a relatively sharp current sheet. Evidence for a substantial deviation from a potential field in the penumbra is found in the analyzed symmetric sunspots. Finally, at the height of line formation the field strength averaged over the whole umbra of all the analyzed sunspots is approximately 2250 G, while the field strength averaged over the whole sunspot is roughly 1350 G. The latter value is similar to the field strength measured in small-scale magnetic features.

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