The magnetic nature of umbra-penumbra boundary in sunspots

0495019 - ASÚ 2019 RIV FR eng J - Journal Article
Jurčák, Jan - Rezaei, R. - Bello González, N. - Schlichenmaier, R. - Vomlel, Jiří
The magnetic nature of umbra-penumbra boundary in sunspots.
Astronomy & Astrophysics. Roč. 611, March (2018), č. článku L4. ISSN 0004-6361. E-ISSN 1432-0746
Institutional support: RVO:67985815 ; RVO:67985556
Keywords : Sun * magnetic fields * photosphere
OECD category: Astronomy (including astrophysics,space science); Computer sciences, information science, bioinformathics (hardware development to be 2.2, social aspect to be 5.8) (UTIA-B)
Impact factor: 6.209, year: 2018

We aim at studying the magnetic nature of umbra-penumbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. We statistically prove that the umbra-penumbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849-1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the umbral size: the larger the umbra, the stronger and more horizontal the magnetic field at its boundary.
Permanent Link: http://hdl.handle.net/11104/0288058