No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

Löptien, Björn; Lagg, A.; Noort, M. van; Solanki, S. K.

doi:10.1051/0004-6361/202037974

Cited by 11 publications

(14 citation statements)

References 55 publications

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“…This result could be consistent with the work done by Lindner et al (2020), who studied the Jurčák criterion (Jurčák et al 2018). This is probably a stability criterion for the UM (though this is still an open discussion, see Löptien et al 2020). For this particular sunspot, they found that the Jurčák criterion applies to part of the LB, meaning it could be related to the part of the LB that has higher inclinations, while the tip would be ascribed to the fact that it is 'under evolution/formation'.…”

Section: Papersupporting

confidence: 90%

Long-term evolution of three light bridges developed on the same sunspot

Griñón-Marín

Yabar

Centeno

et al. 2021

A&A

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One important feature of sunspots is the presence of light bridges. These structures are elongated and bright (as compared to the umbra) features that seem to be related to the formation and evolution of sunspots. In this work, we studied the long-term evolution and the stratification of different atmospheric parameters of three light bridges formed in the same host sunspot by different mechanisms. To accomplish this, we used data taken with the GREGOR Infrared Spectrograph installed at the GREGOR telescope. These data were inverted to infer the physical parameters of the atmosphere where the observed spectral profiles were formed of the three light bridges. We find that, in general, the behaviour of the three light bridges is typical of this kind of structure with the magnetic field strength, inclination, and temperature values between the values at the umbra and the penumbra. We also find that they are of a significantly non-magnetic character (particularly at the axis of the light bridges) as it is deduced from the filling factor. In addition, within the common behaviour of the physical properties of light bridges, we observe that each one exhibits a particular behaviour. Another interesting result is that the light bridge cools down, the magnetic field decreases, and the magnetic field lines get more inclined higher in the atmosphere. Finally, we studied the magnetic and non-magnetic line-of-sight velocities of the light bridges. The former shows that the magnetic component is at rest and, interestingly, its variation with optical depth shows a bi-modal behaviour. For the line-of-sight velocity of the non-magnetic component, we see that the core of the light bridge is at rest or with shallow upflows and clear downflows sinking through the edges.

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Section: Papersupporting

confidence: 90%

Long-term evolution of three light bridges developed on the same sunspot

Griñón-Marín

Yabar

Centeno

et al. 2021

A&A

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“…The penumbral filaments and umbral dots in the small spot are brighter than the ones in the large spot, even though their size is comparable. This decrease of the brightness of penumbral filaments was already reported by Löptien et al (2020).…”

Section: Discussionsupporting

confidence: 85%

“…They interpreted this constant value of B z to be the threshold for the transition from umbra to penumbra. However, their interpretation was later challenged by Löptien et al (2020), who attributed this constant B z to be caused by the decrease of the brightness of penumbral filaments with increasing spot size (see also Fig. 5).…”

Section: Discussionmentioning

confidence: 99%

“…Jurčák et al (2018) suggested that the UP boundary occurs where the strength of the vertical magnetic field falls below a fixed threshold. However, this criterion (often called the Jurčák criterion) does not take into account that the penumbra consists of both filaments and spines, whose properties vary between spots of different sizes (Löptien et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Similarities of magnetoconvection in the umbra and in the penumbra of sunspots

Löptien,

Lagg,

van Noort

et al. 2021

Preprint

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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. Here we compare the physical properties of umbral dots and penumbral filaments. Our goal is to understand how the properties of these convective features change across the boundary between the umbra and the penumbra and how this is related to the rapid increase in brightness at the umbra-penumbra boundary. Methods. We derived ensemble averages of the physical properties of different types of convective features based on observations of two sunspots with Hinode. Results. There are strong similarities between the convective features in the outer parts of the umbra and the ones in the penumbra, with most physical parameters being smooth and continuous functions of the length of the features. Conclusions. Our results indicate that the transition in brightness from the umbra to the penumbra is solely caused by an increased effectiveness of magnetoconvection within individual convective cells. There is no significant difference in the number density of convective elements between the outer umbra and the inner penumbra. Penumbral filaments exhibit a larger area and a higher brightness compared to umbral dots. It is still unclear, how exactly the underlying magnetic field causes the increase in size and brightness of convective features in the penumbra.

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“…Jurčák et al (2018) suggested that the UP boundary occurs where the strength of the vertical magnetic field falls below a fixed threshold. However, this criterion (often called the Jurčák criterion) does not take into account the fact that the penumbra consists of both filaments and spines, the properties of which vary between spots of different sizes (Löptien et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Similarities of magnetoconvection in the umbra and in the penumbra of sunspots

Löptien

Lagg

Noort

et al. 2021

A&A

Self Cite

View full text Add to dashboard Cite

Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, which manifests in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims. Here we compare the physical properties of umbral dots and penumbral filaments. Our goal is to understand how the properties of these convective features change across the boundary between the umbra and the penumbra and how this is related to the rapid increase in brightness at the umbra-penumbra boundary. Methods. We derived ensemble averages of the physical properties of different types of convective features based on observations of two sunspots with Hinode. Results. There are strong similarities between the convective features in the outer parts of the umbra and the ones in the penumbra, with most physical parameters being smooth and continuous functions of the length of the features. Conclusions. Our results indicate that the transition in brightness from the umbra to the penumbra is solely caused by an increased effectiveness of magnetoconvection within individual convective cells. There is no significant difference in the number density of convective elements between the outer umbra and the inner penumbra. Penumbral filaments exhibit a larger area and a higher brightness compared to umbral dots. It is still unclear how exactly the underlying magnetic field causes the increase in the size and brightness of convective features in the penumbra.

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No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

Cited by 11 publications

References 55 publications

Long-term evolution of three light bridges developed on the same sunspot

Long-term evolution of three light bridges developed on the same sunspot

Similarities of magnetoconvection in the umbra and in the penumbra of sunspots

Similarities of magnetoconvection in the umbra and in the penumbra of sunspots

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