Real and imaginary part of the vertical wavenumber as functions of the tidal (σ) and critical (σ_c;n) frequencies. Left: , with defined in Eq. (104), as a function of f⁽σ/σ₀⁾ (horizontal axis) and (vertical axis), where f is the function defined by . The colour of the map, denoted c, is defined by . Hence, the purple region stands for slowly oscillating waves. The luminous (dark) regions correspond to strongly oscillating waves propagating downwards (upwards).Right: as a function of the same parameters. The luminous (dark) regions correspond to strongly (weakly) evanescent waves. The positions of the planets (Earth _⊕, Venus _♀) on the map are determined by the gravity mode of degree 0 in the case of the semidiurnal tide (Λ_⊕;0 = 11.1596, Λ_♀;0 = 7.1485). The tidal frequencies of the planets are given by σ_⊕/σ₀ ≈ 194 and σ_♀/σ₀ = 0.43, with σ₀ = 7.5 × 10^-7 s^-1.