TDs of high-frequencies. Top panel: eight frequencies displaying a similar long-term change: f₃₉ = 13.0064 d⁻¹ (f_parent), f₈₅ = 10.3107 d⁻¹ (f_comb), f₁₀₇ = 15.4706 d⁻¹ (f_parent), f₁₂₃ = 14.8528 d⁻¹ (f_parent), f₁₂₆ = 12.7318 d⁻¹ (f_parent), f₁₄₆ = 12.5150 d⁻¹ (f_parent), and f₁₇₈ = 13.7274 d⁻¹, f₄₃ = 14.3778 d⁻¹. Their mean values are plotted in black. Bottom panel: three frequencies whose behaviour is incompatible with the general trend: f₃₁ = 13.9651 d⁻¹ (f_pmax, in blue), f₅₉ = 14.9697 d⁻¹ (f_parent, in orange) and f₄₄ = 15.9634 d⁻¹ (f_parent, in green), and f₁₇₈ = 13.7274 d⁻¹, f₄₃ = 14.3778 d⁻¹. We re-plotted f₄₃ = 14.3778 d⁻¹ (f_parent, in red) in the lower panel for means of comparison with the frequencies that have incompatible trends in top panel. See Table 6 for the used terminology.