Dark Structures in Sunspot Light Bridges

Jingwen Zhang, Hui Tian, Sami K. Solanki, Haimin Wang, Hardi Peter, Kwangsu Ahn, Yan Xu, Yingjie Zhu, Wenda Cao, Jiansen He, Linghua Wang

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11 Scopus citations


We present unprecedented high-resolution TiO images and Fe i 1565 nm spectropolarimetric data of two light bridges taken by the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory. In the first light bridge (LB1), we find striking knot-like dark structures within the central dark lane. Many dark knots show migration away from the penumbra along the light bridge. The sizes, intensity depressions, and apparent speeds of their proper motion along the light bridges of 33 dark knots identified from the TiO images are mainly in the ranges of 80 ∼ 200 km, 30% ∼ 50%, and 0.3 ∼ 1.2 km s-1, respectively. In the second light bridge (LB2), a faint central dark lane and striking transverse intergranular lanes were observed. These intergranular lanes have sizes and intensity depressions comparable to those of the dark knots in LB1 and also migrate away from the penumbra at similar speeds. Our observations reveal that LB2 is made up of a chain of evolving convection cells, as indicated by patches of blueshift surrounded by narrow lanes of redshift. The central dark lane generally corresponds to blueshifts, supporting the previous suggestion of central dark lanes being the top parts of convection upflows. In contrast, the intergranular lanes are associated with redshifts and located at two sides of each convection cell. The magnetic fields are stronger in intergranular lanes than in the central dark lane. These results suggest that these intergranular lanes are manifestations of convergent convective downflows in the light bridge. We also provide evidence that the dark knots observed in LB1 may have a similar origin.

Original languageEnglish (US)
Article number29
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 20 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Sun: granulation
  • Sun: magnetic fields
  • Sun: photosphere
  • sunspots


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