The spatial correlation between the penumbra disappearance and the filament peeling. (a) GST Hα image taken at 18:21 UT. The box marks a region of interest for the close-up views shown in panels (b)–(f). (b)–(f) The GST images of the Hα center line, Hα+0.6 Å, TiO, Dopplergram, and horizontal field strength ∣B_h∣, all obtained approximately at 18:21 UT. The arrows in these panels point to a strand peeling off from the main body of the filament, and the ovals highlight the area where the penumbra disappears significantly.