Simulated vertical velocity and the response of the Ca II 8542 Å line to velocity changes. Top panel: vertical velocity as a function of height (vertical axis) and time (horizontal axis) at a randomly chosen spatial position. Red lines have the same meaning as those in the bottom panel of Fig. 5. Bottom panel: vertical stratification of the velocity at some selected time steps. The color of the line indicates the corresponding time step, as given by the dashed vertical lines in the top panel.