Evolution of the flow in a longitudinal band of 6° width for each polarity. Left (right) column: leading (trailing) polarity. First (second) row: latitudinal (longitudinal) flow component, and the third row shows the absolute value of the radial magnetic field. The fourth row shows the normalized continuum intensity. All data are time-averaged over six hours. The flows are smoothed with a Gaussian of σ = 0.8°. The curves represent different time steps (see legend).