Panel a): normalized global power (NGP) of the existing periodicities in a typical time series as obtained from the wavelet-based analysis (dot-dashed line), and the Lomb-Normalized periodogram (continuous line). P_i indicates the value in minutes of the most significant periods. All labeled peaks have less than 0.01% probability of being due to white noise. Panels b) through f): NGP from the wavelet-based analysis to show how the determination of the background affects the relative intensity of a given period. The number of iterations [n] performed to obtain the different background trends is indicated on each panel along with the value of the dominant period P_D. The dashed line in all panels indicates the 95% confidence level for the wavelet-based method. For details see Sect. 3.3. The example shown corresponds to a time series obtained for the slit at the location depicted as A in Fig. 4 at a distance from the slit origin of 36 000 km (on 2008/03/25).