Extended Data Fig. 2: MFR buildup during the flare precursor phase.
From: Complete replacement of magnetic flux in a flux rope during a coronal mass ejection
From the top to bottom are SDO/AIA 131 Å base-difference images, ratio of SDO/AIA 1600 Å and 1700 Å images, SDO/AIA 131 Å images zooming in on the eastern foot of the sigmoid, and simultaneous IRIS SJI 1400 Å images (Methods). The white dotted rectangle in panel (b) indicates the FOV of panels (c & d). Three white lines in panels (a & d) indicate the virtual slits S1-S3 for the stack plots in Fig. 4(c–e) (Methods), whose starting points are labeled as ‘0’. The yellow arrow in the IRIS image indicates the extending direction of the ribbon. Yellow dotted lines in the AIA 131 Å image at 17:12 UT denote the location of the trapezoidal ribbon observed in IRIS 1400 Å at the same time (see also Fig. 5a & d).
