Dark Structures in Sunspot Light Bridges

Abstract

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 blue shift surrounded by narrow lanes of red shift. 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.

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

“…9. Within the light bridge (see the orange rectangle), low-lying magnetic structures (see the green curves) continuously emerge through long-lasting convection upflows from the solar interior to the solar atmosphere (Lites et al 1991;Rueedi et al 1995;Leka 1997;Jurčák et al 2006;Rouppe van der Voort et al 2010;Toriumi et al 2015a,b;Zhang et al 2018b). They are then restricted in the lower solar atmosphere by the above strong umbral fields (see the blue curves), which form a magnetic canopy covering the light bridge (Jurčák et al 2006).…”

Light Bridges Can Suppress the Formation of Coronal Loops

“…This configuration is driven by magnetoconvection process as demonstrated with radiative MHD simulation by Rempel (2011) andSiu-Tapia et al (2018). Within the nearly horizontal magnetic field of a light bridge, the gas pressure of restored convection could become dominate and drags the magnetic field downward, and even results in reversed polarities at a light bridge at extreme cases (Lagg et al 2014;Felipe et al 2016;Zhang et al 2018;Guglielmino et al 2017). Due to the strong discontinuity between the magnetic field of the light bridge and umbra, a strong electric current layer could be detected at the edges of a light bridge (Toriumi et al 2015b).…”

Recent research progress of solar physics in China

“…(a) 太阳黑子及其本影中的亮桥; (b) 亮桥上的暗结 [49] ; (c) 亮桥上的倒Y型喷流 [50] Figure 1 (Color online) Observations of sunspot light bridges by Goode Solar Telescope (GST). (a) A sunspot with a light bridge (marked by a rectangle) spanning across the umbra; (b) dark knots on the light bridge in (a) [49] ; (c) inverted Y-shaped jets on a light bridge [50] 通过研究这些波动和振荡来诊断日冕磁场, 被称为"冕 震学". 与太阳爆发活动相关的大尺度波动穿越活动区 和冕洞或作用于暗条等结构表现出的观测特征与快模 磁声波相符 [51~54] .…”

“…Yang等人 [48] 发现太阳黑子亮桥(图1(a))上存在由许多 喷流组成的振荡的亮墙结构. Zhang等人 [49] 发现窄亮桥 上存在很多暗结(图1(b)), 由此提出亮桥磁对流的新图 像. Tian等人 [50] 指出亮桥上的喷流有两个分量: 一个是 整个亮桥上由激波驱动的重现性慢速喷流(约15 km/s),…”