Fourier power spectrum of the resampled USET time series, assuming 206 observations spread over 10 years for an equator-on view. The top panel illustrates the logarithm of the power spectrum for frequencies below 0.05 d⁻¹. The long-dashed blue line marks the 99% significance level. The bottom panel provides a zoom-in on the power spectrum around ν_Car (given by the short-dashed magenta vertical line) after removing the long-term trend from the data. The long-dashed red line indicates the 99% significance level for the detrended time series. The magenta vertical lines in the top and bottom panels indicate the Carrington rotation frequency.