Snapshots of the vertical velocity ﹩{\tilde{u}}_{z}﹩ at ﹩\tilde{y}=0﹩ in the saturated state for simulations with Pr = 10⁻⁶, τ = Pr/2, and (a) ﹩{ \mathcal R }=1.1﹩, (b) ﹩{ \mathcal R }=11﹩, and (c) ﹩{ \mathcal R }=301﹩ (or ε = 0.1, 10, and 300). As ﹩{ \mathcal R }﹩ increases, velocity fluctuations increase and develop finer structures.