Formation of δ sunspot. Panels a1–h1 display the photospheric B_z magnetograms, with B_z saturating at ±1200 G, while panels a2–h2 are the continuum images. Label P_A denotes a pre-existent positive polarity. N₁ and P₁ indicate the negative and positive polarities of bipole1, respectively, while N₂ and P₂ are for bipole2. and denote two patches of P₁. The newly formed , which is located at the north of N₂, is further indicated by a cyan arrow in panels f1–h1. The labels , , , and in panel h1 are discrete patches of P2, corresponding to different field lines in Fig. 5. The green rectangle in panel h1 indicates the FOV of Fig. 3. The red circle in (h2) marks the δ sunspot configuration. An associated animation is available online.