Time sequence of the absolute magnetic field strength at z = 0 (gray scale) in the same field of view as shown in Fig. B.1. Plotted on top of the field strength is the vertical component of the swirling vector λ_z in regions where λ > 10⁻³ Hz and λ^B > 10⁻⁶ G cm⁻¹. Red indicates counterclockwise and blue clockwise rotation, that is, positive and negative values of λ_z, respectively.