Illustrations of the field lines above the polarity inversion line for the simulation where ζ = −175 km² s⁻¹ at 10:58 UT on 5 April 2017. The field lines are shown at low (top) and high (middle and bottom) heights above the PIL. The colour coding represents the strength of the electric current, defined as J = ∇ × B along the field lines as given in the right-hand side (Log(J) ranging from 1 to 3). The background image represents the photospheric magnetogram where red represents positive flux and blue negative flux in the range ±50 G, left-hand sub-panel.