Three-dimensional (3D) magnetic fields above F1 and F2 revealed by NLFFF extrapolation at 22:00 UT on November 15. (a): Overlying loops of F1 and F2, forming a quadrupole magnetic field configuration. (b)–(c): Top view and side view of 3D distribution of magnetic field strength with values between 5 and 25 Gauss in the selected cube. (d)–(e): Distributions of magnetic field strength and decay index in the vertical plane based on the dark blue cut denoted in (a). The null point of the quadrupole magnetic configuration is distinctly depicted at a height of ∼90 Mm. (f): Height profiles of decay index averaged within two regions defined by two blue lines and two red lines in the vertical plane of (e), respectively.