Median of the standard error against averaging time. The lines in the top panel show the cases of no smoothing (yellow) and of Gaussian smoothing of 0.4, 0.8, 1.2, 1.6, 2.0, and 4.0° (green to purple). All lines are from an ensemble average over all 182 ARs. The dotted line shows the least-squares fit to the case of Gaussian smoothing of σ = 1.6°. Bottom: Same as in the top panel for averages over 5, 10, 20, 45, 60, 91, and 182 control regions (yellow to purple). All lines are with a Gaussian smoothing of σ = 0.8°. Both panels show the case of the latitudinal flow component. The scale of the y-axis is different in the two panels.