Fourier power spectrum of the fractional area of the plages and enhanced network in the case of an inclination i = 0° (equator-on view). The upper and middle panels correspond to the power spectrum of the original data, while the lower panel gives the power spectrum of the time series detrended for the long-term cycle. The dashed blue lines in each panel illustrate the 99% significance level for the original time series, while the dashed red line in the bottom panel corresponds to the 99% significance level of the detrended time series. The magenta vertical lines in the top and bottom panels indicate the Carrington rotation frequency.