Solar cycle variations in the seismic average mode frequency shift from Howe et al. (2017) (A), the seismic average travel time (B) and photometric variability (C). The orange curve connects the data points. The data analyzed here was divided into overlapping time segments of T = 1 yr in length and mid-points separated by Δt = 91.25 d. (D, E) Power spectra of the activity observables shown in panels A–C. All power spectra are normalized to the power at frequency 1/(9 yr). The abscissa shows the period in the left panel and the frequency in the right panel.