Exemplary amplitude evolution of selected modes of the fast wave model (showing m = 1, m = 2, as well as the superposition m = 1, 2). The time is normalized to the light crossing time of the computational domain (τ). Left: field amplitude at the point y = 0 for a superposition of modes m = 1,  2 (top panel), m = 2 (middle), and m = 1 (bottom). The analytic solution is indicated in the background (thick magenta lines). Different resolutions are visualized by solid (N_y = 12) and dotted (N_y = 24) lines. Right: evolution of the energy contained in the perturbations, given by Eq. (8), scaled to (squares) and theoretical model (solid lines for N_y = 12 and dashed lines for N_y = 24) employing the fit parameters from Table 1. Mixed modes evolve according to a superposition of two exponentially damped plasma waves with the appropriately scaled damping rates inferred from Fig. 1.