Maps of the in-plane magnetic field, $B_{\mathrm{pl}}=\sqrt{{B_x}^2+{B_y}^2}$ (left panels, colour coded) and of the two components of the velocity field, u_x and u_y (central and right panels, colour coded), at t = 16. The pinch tracer edge is drawn as a solid black line. Top and bottom panels represent runs Y3k and Y3 respectively, which differ in the excited scales of initial random fluctuations: run Y3k has k≥4k_FR and run Y3 has k≥k_FR.