Snapshots of field lines traced from points on a slit crossing through the sunspot scar in the positive polarity during 66 ≤ t ≤ 68 in “Simulation 2”. The bottom plane in each sub-panel exhibits the vertical magnetic field strength on the plane z = 0.1. In panels a–c, the thin yellow, green and blue tubes represent the field lines traced from points on a slit which is along the slit in Fig. 10; the thick purple tube represents the field line which is traced from a fixed point at the bottom plane (z = 0.015) and crosses through the plane z = 0.1 with the intersection in the sunspot scar and on the slit. The red filled contours show the QSLs footprints on the plane z = 0.1. Panels d–f show the top view of panels a–c, with only the plane z = 0.1 and the thick tube (same as the purple tube in panels a–c) exhibited. The color of the tube shows the temperature along the field line.