Instability growth rate for the 2D Kelvin-Helmholtz instability test shown in Fig. 1. This growth rate is estimated from the evolution of the quantity ∂ ln $u_z^{max}/\mathrm{\partial }t$ and for three different grid choices, corresponding to “Low” (blue), “Med” (red), and “High” (green) resolution (i.e., [n_x, n_z] = [512, 256], [1024, 512], and [2048, 1024]). The dashed line corresponds to the best-fitting exponential to the growth rate in the linear regime, which breaks down at t ~ 2.6.