HMI intensity maps (top row) and magnetic field strength (middle row) and magnetic field inclination (bottom row) of the AR 12757 on January 26, 2020. Magnetic field inclination is shown only in pixels with B > 150 G. Maps corresponding to the start and end times of our analysis are shown in the left and right panels, respectively. The middle panels show the active region in the middle of the analysed time period. The green and magenta contours show the umbra/penumbra and penumbra/quiet Sun boundaries, respectively. The black oval contours show the distance from the ellipse centre at r/r₀ = 1, 2, 3, where r₀ is the “radius” of the ellipse fitted to the penumbra/quiet Sun boundary at the end time of the analysed time period. The red dashed contours show our region of interest (ROI). The temporal evolution of a close-up of the are under study is available online.