Time sequence of prominence PC in Hα images, AIA 171 Å images in logarithmic scale, and LOS magnetograms on November 15 (a–c), November 17 (d–f), November 18 (g–i), and November 19 (j–l) in 2011. The small circles in different colors show the locations of the footpoints of prominence legs. The diameter of these circles is 8 arcsec (about 5800 km). The magnetograms in gray are Gaussian smoothed and saturated at ±30 G. Supergranular boundaries are indicated by dashed lines in different colors connecting strong magnetic elements in the HMI magnetograms.