Case of ϵ = 0.2 and St = 0.01 (model E0v02S0v01c), showing the time evolution of the dimensionless diffusion coefficients, α_g,i, in each direction (top). The lower panel shows the expected linear growth rates for the same model in the inviscid case (left) and for α_g,i = 5 × 10⁻⁶ (right). These have been obtained from linear theory (see Appendix A) using D = ν = α_g,ic_sH_g. Here, ${\tilde{K}}_{x,z}=k_{x,z}\eta R_0$ are the dimensionless wavenumbers.