Power spectra of south-north travel-time shifts for modes in the range 3 ≤ m ≤ 14 (black curves, with the frequency resolution 1/T = 4.5 nHz). The travel times are measured in the frame rotating at equatorial rotation rate Ω_eq/2π = 453.1 nHz. The red lines are the fits F_m(ω) given by Eq. (8). The green vertical lines indicate the mode frequencies from Löptien et al. (2018). The orange arrows mark the excess low-frequency power at low m that might be caused by active regions or large-scale convection. The purple arrows mark the leaks from the m − 1 r-mode power and the low-frequency power at m − 1. Each power spectrum is accompanied by a plot of the ratio in gray in the lower panel, which is expected to have a mean of unity (dashed line) and a constant variance if the fit is not biased.