Time evolution of the volume-averaged variables in the 3D (solid lines) and 1D settings (dashed lines). The horizontal axis (time) is normalized by the period of the parent wave τ₀. Panels indicate the (a) normalized rms density fluctuation ﹩\delta {\rho }_{\mathrm{rms}}/{\rho }_{0}﹩, (b) angle between current density and magnetic field ϕ_j,B, (c) normalized Elsässer energies (red: E⁺/E₀, blue: E⁻/E₀), and (d) normalized cross-helicity σ_c, respectively. The blue lines in panel (a) are the exponential fitting ﹩\delta {\rho }_{\mathrm{rms}}\propto \exp (\gamma t)﹩ in the linear growth stage.