Example of the data analysed in this study. Top: photospheric circular polarization map saturated between −3% and 3%. Centre: chromospheric broadband image of the same region. The 35 longest-lived magnetic elements used in the analysis are highlighted with yellow circles. The red crosses mark the six elements whose power spectra are shown in Fig. 3 (see text for more details). Bottom: continuum image taken at 395.3 nm with 1 Å bandpass.