Forces that enter in the x-momentum equations at z = 0 for neutrals only (solid lines): pressure gradient (dark blue) and viscous force ∇ ⋅ τ_nx (black), where with ξ_n defined by Eq. (A.9) in Popescu Braileanu et al. (2019); for charges only (dashed lines): the pressure gradient (light blue) and the Lorentz force (green); and the ion-neutral collisional coupling between neutrals and charges R_n = αρ_nρ_c(v_nx−v_xc) (dotted line), with the collisional parameter α defined by Eq. (A.8) from Popescu Braileanu et al. (2019) for the two simulations: P (left panel) and L2 (right panel).