Magnetic flux distribution and surface rotation flow at the bottom end (i.e., z = 0). The background is color-coded by the vertical magnetic component B_z, and the vectors show the rotation flow. The four panelsA, B, C, and D refer to magnetogram with σ_y = 0.5, 1.0, 1.5, and 2.0 respectively, while σ_x = 2.0 and y_c = 0.8 are fixed. We note that the values of σ_x, σ_y, and y_c are normalized by a unit length of 14.4 Mm.