Properties of the convective flows. Left: ratio of rms values of horizontal and vertical flow velocity on surfaces of constant geometrical depth. Right: estimated horizontal scale of the vertical velocity patterns as derived from Eq. (1) on surfaces of constant geometrical depth. The horizontal scale is given in units of the horizontal box size, X_tot, for an easier comparison with Figs. 3 and 4. The solid curves refer to the four simulations shown in these figures, the dashed curves to the remaining two simulations.