Panel a: contour plot of the horizontal mean of the density for B1. Panel b: same for B8. Panel c: same for W4. The dashed white and black lines signify α = −0.047 and α = 0.047, respectively, for panel a, α = −0.055 and α = 0.0354 for panel b, and α = −0.044 and α = 0.038 for panel c. Panel d: mean density distribution plotted against z/Agt² for the final 200 snapshots of the simulation for B1. Panel e: same but for B8. Panel f: same but for W4. Note that the values that would be calculated for α from this figure are over estimates due to the initial expansion of the system.