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Context.Light bridges are bright, long, and narrow features that are typically connected to the formation or decay processes of sunspots and pores. Aims.The interaction of magnetic fields and plasma flows is investigated in the trailing part of an active region, where pores and magnetic knots evolve into a complex sunspot. The goal is to identify the photospheric and chromospheric processes, which transform the mainly vertical magnetic fields of pores into a sunspot with multiple umbral cores, light bridges, and rudimentary penumbrae. Methods.Conducting observations with a broad variety of telescopes and instruments provides access to different atmospheric layers and the changing morphology of features connected to strong magnetic fields. While the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) provides full-disk continuum images and line-of-sight magnetograms, the fine structure and flows around a pore can be deduced from high-resolution observations in various wavelengths as provided by theGoodeSolar Telescope (GST) at the Big Bear Solar Observatory (BBSO). Horizontal proper motions are evaluated applying local correlation tracking (LCT) to the available time series, whereas the connectivity of sunspot features can be established using the background-subtracted activity maps (BaSAMs). Results.Photospheric flow maps indicate radial outflows, where the light bridge connects to the surrounding granulation, whereas inflows are present at the border of the pores. In contrast, the chromospheric flow maps show strong radial outflows at superpenumbral scales, even in the absence of a penumbra in the photosphere. The region in between the two polarities is characterized by expanding granules creating strong divergence centers. Variations in BaSAMs follow locations of significant and persistent changes in and around pores. The resulting maps indicate low variations along the light bridge, as well as thin hairlines connecting the light bridge to the pores and strong variations at the border of pores. Various BaSAMs demonstrate the interaction of pores with the surrounding supergranular cell. The Hαline-of-sight velocity maps provide further insights into the flow structure, with twisted motions along some of the radial filaments around the pore with the light bridge. Furthermore, flows along filaments connecting the two polarities of the active region are pronounced in the line-of-sight velocity maps. Conclusions.The present observations reveal that even small-scale changes of plasma motions in and around pores are conducive to transform pores into sunspots. In addition, chromospheric counterparts of penumbral filaments appear much earlier than the penumbral filaments in the photosphere. Penumbra formation is aided by a stable magnetic feature that anchors the advection of magnetic flux and provides a connection to the surrounding supergranular cell, whereas continuously emerging flux and strong light bridges are counteragents that affect the appearance and complexity of sunspots and their penumbrae.
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Automatic segmentation of the fine structures of sunspots in high-resolution solar images
Context. With the development of large-aperture ground-based solar telescopes and the adaptive optics system, the resolution of the obtained solar images has become increasingly higher. In the high-resolution photospheric images, the fine structures (umbra, penumbra, and light bridge) of sunspots can be observed clearly. The research of the fine structures of sunspots can help us to understand the evolution of solar magnetic fields and to predict eruption phenomena that have significant impacts on the Earth, such as solar flares. Therefore, algorithms for automatically segmenting the fine structures of sunspots in high-resolution solar image will greatly facilitate the study of solar physics. Aims. This study is aimed at proposing an automatic fine-structure segmentation method for sunspots that is accurate and requires little time. Methods. We used the superpixel segmentation to preprocess a solar image. Next, the intensity information, texture information, and spatial location information were used as features. Based on these features, the Gaussian mixture model was used to cluster different superpixels. According to different intensity levels of the umbra, penumbra, and quiet photosphere, the clusters were classified into umbra, penumbra, and quiet-photosphere areas. Finally, the morphological method was used to extract the light-bridge area. Results. The experimental results show that the method we propose can segment the fine structures of sunspots quickly and accurately. In addition, the method can process high-resolution solar images from different solar telescopes and generates a satisfactory segmentation performance.
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- Award ID(s):
- 1821294
- PAR ID:
- 10408427
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 670
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A132
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1051/0004-6361/202244224
