Initial distribution of the magnetic field strength in the original (top) and our Bifrost (bottom) simulation. The magnetic field is shown at two horizontal cuts of the computational domain: at the base (z = 0 Mm, solid lines) and top (z = 1.26 Mm, dashed lines). The black and red lines indicate the vertical (B_z) and horizontal (B_x) magnetic field strengths, respectively. The vertical dotted lines indicate the three different segments of B_z where the flux is either positive (∼2 Mm wide) or negative (∼750 km wide). The shaded area indicates the location of the 400 km wide piston. This plot is for the strong field case. For the weak field, the field strengths are divided by 4 everywhere.