Vertical mechanical flux spectra at (a) a height of z = 560 km and at (b) the Rosseland mean optical depth layer of τ_R = 1 × 10⁻⁴. Also shown are the vertical energy flux spectra estimated from phase difference measurements of (c) velocities at two layers of constant optical depth: τ_R = 5 × 10⁻⁶ and τ_R = 1 × 10⁻³ and from (d) the line-minima shifts of the Fe I λ 5434 Å and Fe I λ 5576 Å lines. The plot is masked to show only the IGW region. The grey curve marks the dispersion relation of the surface gravity waves. The black dashed curves mark the propagation boundary of acoustic-gravity waves corresponding to approximately the middle region of the two layers.