Left panel: sedimenting particles with a k_z = π/ 2-mode in the particle density. Represented is a snapshot of runRT at t = 5t_f. No instabilities develop, suggesting that the drafting instability is not directly related to the Rayleigh-Taylor instabilities that should occur in this set up. Right panel: evolution of the sedimenting particle wave at an arbitrary placed slice at x = −0.23. Different curves represent different times (t = 0,1,2,...,6t_f), that for clarity are offset by 0.2. The particle density ρ_p(z) is given in black, while the red dashed line gives the gas velocity u_z(z). Particle ridges do not approach each other, as indicated by the blue line that tracks the position of a point advected with velocity v_f. The pressure that is supporting the mass-loaded stratification adapts to compensate for small changes in the particle density. This allows u_z(z) to remain zero while the particles sediment.