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

0479157 - ASÚ 2018 RIV FR eng J - Journal Article
Jurčák, Jan - Gonzalez, N.B. - Schlichenmaier, R. - Rezaei, R.
A distinct magnetic property of the inner penumbral boundary II. Formation of a penumbra at the expense of a pore.
Astronomy & Astrophysics. Roč. 597, January (2017), A60/1-A60/4. ISSN 0004-6361. E-ISSN 1432-0746
R&D Projects: GA ČR(CZ) GA14-04338S
Institutional support: RVO:67985815
Keywords : Sun * magnetic fields * photosphere
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 5.565, year: 2017
Method of publishing: Open access

Here, we aim to study the development of a penumbra initiated at the boundary of a pore, where the penumbra colonises the entire pore ultimately. We have used Hinode/SOT G-band images to study the evolution of the penumbra. Hinode /SOT spectropolarimetric data were used to infer the magnetic field properties in the studied region. The penumbra forms at the boundary of a pore located close to the polarity inversion line of NOAA10960. As the penumbral bright grains protrude into the pore, the magnetic flux in the forming penumbra increases at the expense of the pore magnetic flux. Consequently, the pore disappears completely giving rise to an orphan penumbra. At all times, the vertical component of the magnetic field (B-ver) in the pore is smaller than B-ver found on stable umbra-penumbra boundaries (B-ver-stable), which is around 1.8 kG. Our findings are in an agreement with the need of B-ver-stable for establishing a stable umbra-penumbra boundary: while B-ver in the pore is smaller than B-ver-stable, the protrusion of penumbral grains into the pore area is not blocked, a stable pore-penumbra boundary does not establish, and the pore is fully overtaken by the penumbral magneto-convective mode. This scenario could also be one of the mechanisms giving rise to orphan penumbrae.
Permanent Link: http://hdl.handle.net/11104/0275153