Region of interest A: (a) The time evolution of the continuum at 4000 Å, LOS magnetic field (B_LOS), and images at wavelength offsets of −108.2 mÅ, +22.6 mÅ, and +153.3 mÅ from the core of the Ca II K line are shown column-wise. Panels b and c display λ–t diagrams for the pixel marked with a “+” in panel a in the Ca II K and Ca II 8542 Å lines, respectively. A gamma correction with γ = 0.85 was applied on the Ca II K narrowband images in panel a, and γ = 0.1 on panels b and c. A few selected profiles marked in panels b and c are shown in panels d and e. The outer contour (cyan) is made with pixels belonging to RPs 85, 36, 18, and 78, while the middle contour (azure blue) is made with RPs 18 and 78 in panel a. The inner contour (navy blue) shows the region belonging to RP 78, the strongest CBG RP. The dashed vertical lines in panel d show the position of the narrowband images in panel a.