Runs D and H (weak and strong χ₀): frequency energy spectra E⁺(f),   E⁻(f), computed by taking the Fourier transform of the at each plane and then space averaging separately in the chromosphere (bottom black and red lines) and corona (top black line). The E⁻ (not plotted) and E⁺ coronal spectra are indistinguishable. The vertical lines mark some relevant timescales: dotted lines for the resonances at n ≥ 1; dot-dashed lines for the (round-trip) chromospheric crossing time, ; and long-dashed lines for the leakage time, t_L.