Analysis of σ_nt/v_rms. (a) σ_nt/v_rms as a function of height (z) for the v_y : H simulation in the Alfvén wave model. The orange line has an exposure time equal to the period of the driver, and the blue line has an ‘infinite’ exposure time (full length of the simulation). The dashed horizontal line is at . The asterisks are evaluated at (x′,z) = (0.1, −28.6) Mm during a time frame before (green and red) and after (purple) wave reflection off the top boundary, with exposure times equal to one period (15 s: green and purple) and one and a half periods (22.5 s: red) of the velocity driver. (b) Time frames for the asterisks described in (a), depicted by the vertical bars (corresponding colours) on top of v_y at the point (x′,y′,z) = (0.1, 0.1, −28.6) Mm as a function of the time (black line). Left and right-hand panels: are from approximately 0−120 s and 605−725 s, respectively.