Wavelet decomposition of the time series for one pixel. The background is the same for the four panels and the colour scale is the wavelet power normalised by the calibrated wavelet power (five times the estimated noise level of the magnetic field inclination). The x-axis corresponds to the time sequence and the y-axis is the period. The horizontal line, dashed line, solid contours, and red gridded area reflect the different criteria for the event selection explained in Sect. 2.