Distributions of force-free parameter (α_z), vertical electric current density, proxy of heilicty flux density (G_θ); panels a1–a4: force-free parameter (α_z); panels b1–b4: vertical electric current density (J_z). The pink and black contours denote the positive and negative magnetic field with the levels of 500 G, 1500 G, respectively; panels c1–c4: proxy of helicity flux density (G_θ). It only plots the pixels with the total magnetic field strength bigger than 300 G.