Results of the Hilbert-Huang analysis. Left panel: second-order Hilbert spectrum ℒ₂(f) (blue circles), the classical Fourier PSD (Welch 1967) E(f) (red line), and the second-order structure function S₂(ℓ_t) (green squares, plotted as a function of the inverse timescale ℓ_t), for sample 1. Power scaling is present in the same frequency range for all methods. The dashed line represents the classical Kolmogorov scaling ℒ₂(f)∼f^−5/3, while the dotted line represent the expected scaling for the second-order structure function (ζ(2) = β₂ − 1). Central panel: generalized Hilbert spectra ℒ_q(f) for q ∈ [1, 5], obtained for sample 1. The curves have been vertically shifted for clarity. The shaded area represents the frequency range of the bootstrapping least-square fit. Right panel: same as in the central panel but for sample 9. The power behavior is still present, but the power law exponents are considerably different.