Related papers: A distinct magnetic property of the inner penumbra…
We recently presented evidence that stable umbra-penumbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, $B^{\rm stable}_{\rm ver}$. In order to trigger the formation of a…
Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto…
It was empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. We analyzed the evolution of the photospheric magnetic field properties of a decaying…
The magnetic properties of the umbra-penumbra (UP) boundary of sunspots and the boundary of pores at various evolutionary stages have been characterised using datasets from different instruments. We aim to study the differences between the…
The analyses of sunspot observations revealed a fundamental magnetic property of the umbral boundary, the invariance of the vertical component of the magnetic field. We aim to analyse the magnetic properties of the umbra-penumbra boundary…
Context. In a recent statistical study of sunspots in 79 active regions, the vertical magnetic field component $B_\text{ver}$ averaged along the umbral boundary is found to be independent of sunspot size. The authors of that study conclude…
The vertical component of the magnetic field ($B_\perp$) was found to reach a constant value at the umbra-penumbra boundary of stable sunspots in a recent statistical study of Hinode/SP data. The objective of this work is to verify the…
Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength…
We study the formation of a sunspot penumbra in the active region NOAA11024. We simultaneously observed the Stokes parameters of the photospheric iron lines at 1089.6 nm with the TIP and 617.3 nm with the GFPI spectropolarimeters along with…
Penumbrae are known to be area of mainly horizontal magnetic field surrounding umbrae of relatively large and mature sunspots. In this paper, we observationally studied the formation of penumbrae in NOAA10978, where several penumbral…
Context. Analyses of magnetic properties on umbrae boundaries led to the Jurcak criterion, which states that umbra-penumbra boundaries in stable sunspots are equally defined by a constant value of the vertical magnetic field, Bver_crit, and…
The generation of magnetic flux in the solar interior and its transport to the outer solar atmosphere will be in the focus of solar physics research for the next decades. One key-ingredient is the process of magnetic flux emergence into the…
12 stable single sunspots were investigated in two aspects. The outer boundaries of the sunspots umbra were determined by an independent mathematical method and the vertical component of the magnetic field at these boundaries was found. We…
Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, manifesting in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims.…
Context. Fully fledged penumbrae have been widely studied both observationally and theoretically. Yet the relatively fast process of penumbra formation has not been studied closely with high spatial resolution. Aims. We investigate the…
Solar magnetic fields are generated in the solar interior and pop up at the solar surface to form active regions. As the magnetic field appears on the surface, it forms various structures like small magnetic elements, pores, and sunspots.…
Jurcak et al (2018) have reported that, in a sample of more than 100 umbral cores in sunspots, the umbral-penumbral boundary (UPB) is characterized by a remarkably narrowly-defined numerical value (1867 G) of the vertical component of the…
Penumbrae are the manifestation of magnetoconvection in highly inclined (to the vertical direction) magnetic field. The penumbra of a sunspot tends to form, initially, along the arc of the umbra antipodal to the main region of flux…
Sunspot penumbrae show a fine structure in continuum intensity that displays considerable dynamics. The magnetic field, in contrast, although also highly structured, has appeared to be relatively static. Here we report the discovery of…
Context : Penumbrae are an important characteristic of sunspots, whose formation is intricately related to the nature of sub-photospheric magnetic fields. Aims : We study the formation of a penumbra in a decaying sunspot and compare its…