Separation velocity of the polarities in the east-west direction, , (top panel) and the north-south direction, , (bottom panel) at the emergence time, TI+00, as a function of latitude, λ. The size of the circle is proportional to the maximum flux of the active region. The thick black points with error bars show the averages over different ranges of latitude (between 0 and 15° (sin λ = 0.26) and 15° to 40° (sin λ = 0.64) in the northern hemisphere, and the equivalent in the southern hemisphere). The dashed lines are the mean values.