A distinct magnetic property of the inner penumbral boundary. II. Formation of a penumbra at the expense of a pore

Jurčák, J.; Bello González, N.; Schlichenmaier, R.; Rezaei, R.
Bibliographical reference

Astronomy & Astrophysics, Volume 597, id.A60, 4 pp.

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Context. We recently presented evidence that stable umbra-penumbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, Bstablever. In order to trigger the formation of a penumbra, large inclinations in the magnetic field are necessary. In sunspots, the penumbra develops and establishes by colonising both umbral areas and granulation, that is, penumbral magneto-convection takes over in umbral regions with Bver