Skewness of vertical velocity S_w in 3D RHD simulations of solar granulation. Top: Open vertical boundary conditions at top and bottom (using the code of Muthsam et al. 2010). Bottom: Closed vertical boundary conditions (using the code of Robinson et al. 2003). Data directly computed from the 3D RHD numerical simulations (purple line with crosses) are compared with the new TOM model and the DGA. For the new TOM model, the green line with x-shaped points shows the no damping case (c₆ = 0). The full, new model (c₆ = 0.1) is indicated by a dark blue line with circles. The light brown line with asterisks denotes the DGA (d₃ = −0.1). The light blue line with squares shows the DGA with ten times larger turbulent diffusivity (d₃ = −1).