Snapshots of the ROI (first column) taken by SDO/AIA at approximately 00:00 UT for 1700 Å, 1600 Å, 304 Å, and 171 Å (from top to bottom). Maps (from second to fourth column) showing the power distribution obtained from the periodograms calculated for each pixel of the ROI over three one-minute intervals between 2 and 5 min. The second column corresponds to the main powers obtained in the interval [2–3] min, the third to [3–4] min, and the last one to [4–5] min. The colour scales in the different columns are normalised to the same value for comparison.