a) Evolution of the velocity of small granules in the simulation at the τ₁-iso-surface (blue line) and the log τ_-1-iso-surface (red line). b) Small granules in observations. c) Evolution of the velocity of large (>1700 km; blue) and medium-sized (800 km <d< 1700 km; red) granules in the simulation at the τ₁-iso-surface (solid line) and the log τ_-1-iso-surface (dashed line) with time. d) Evolution of the vertical velocity of large granules (>1700 km; blue line) and medium-sized (800 km <d< 1700 km; red) granules with time in observations. The error bars of the curves represent the standard deviation with a confidence interval of 1-σ.