Power spectrum ℓ(ℓ + 1/2) C_ℓ/(2π) of a turbulent component of index α_M = −2.5, as a function of the multipole ℓ. The differential energy lost by smoothing the maps from an initial resolution ω₁ = 80′ to ω₂ = 160′ is filled in orange, representing a fraction of the original power in the turbulent component (see text in Appendix F.8 and Eq. (F.54)). Shown as hatched is the turbulent energy implied in the calculation of 𝒮 at a resolution of ω = 80′ (with δ = ω/2 = 40′), which is a fraction of the original power in the turbulent component (see text in Appendix F.7 and Eq. (F.51)). Both coloured and hatched regions scale with the resolution ω as ω^{−2 − α_M}.