Spectrum evolution for the 2D simulation of Alfvén interactions initialized according to Eq. (78). We show the spectral energy distribution for wavenumbers k_⊥ (perpendicular to the guide field) in analogy to Fig. 6, Li et al. (2019). Top: spectral energy distribution at different times for the resolution 512². Bottom: spectral energy distribution for selected times and wavenumbers (color code as in top panel) and different resolutions, indicated by dashed (128²), dotted (256²) and solid (512²) lines. No visible convergence is reached.