Time-averaged absolute magnetic field strength, , at the optical depth levels a) τ₁ = 1; b) τ₂ = 0.0008; and c) τ₃ = 6.7  ×  10^-5. The average is taken over the entire time series of 1250 s. The horizontally averaged position of the considered optical depth levels corresponds to the geometrical heights,  ⟨ z(τ₁) ⟩  = 0 km,  ⟨ z(τ₂) ⟩  ≈ 400 km, and  ⟨ z(τ₃) ⟩  ≈ 600 km. The white contour represents the time-averaged position of the equipartition level where c_A = c_s.