a) v_r at z = 0 (solid line in arbitrary units) as a function of time in a prominence fine structure with L_p/L = 0.1, v₀/v_Ap = 0.05, and z₀ = 0. The initial excitation is the fundamental kink mode eigenfunction for v₀ = 0. The dashed line is the amplitude in the WKB approximation (Eq. (22)), while the dotted line corresponds to the fit proposed in Eq. (26) with n = 1. b) Wavelet power spectrum for the dimensionless period, P/τ_Ap, corresponding to the signal displayed in panel a). The white dashed line is the period in the WKB approximation (Eq. (23)), whereas the horizontal dotted line is the period at t = 0. The red solid line denotes 99% of confidence level. c) Same as panel a) but for L_p/L = 0.2, v₀/v_Ap = 0.1, and z₀/L =  −0.25. d) Same as panel b) but for the signal of panel c), and with the horizontal dotted line denoting the maximum of the period.