Left: close-ups on the flow at the sites of the events E1 till E6 shown in Fig. 4. The flows are averaged over 1 h and smoothed over 4 Mm. The coloured background is the magnitude of the horizontal flow velocity. The black lines are the streamlines and the arrows indicate the flow direction. Right: same FOVs with the supergranular boundaries displayed as blue lanes; the green and red contours (respectively) are the magnetic field at −5 G and + 5 G from the 4 h-averaged MDI magnetogram. The blue lanes are darker when they surround bigger, more persistent supergranules, and lighter for smaller, noisier supergranular boundaries.