2D power maps at the 4 and 5 min period bands (top and bottom row, respectively) in the Hα ± 1.03 Å, Hα ± 0.77 Å, Hα ± 0.26 Å, Hα line centre, Hα Doppler velocity, and FWHM for the second observing period (08:28 UT–09:16 UT). The two period bands of 1 min width are centred around the respective periods, while the greyscaling in each panel is within ±2σ from the respective mean power value of the whole image, with σ corresponding to the respective standard deviation. The overplotted yellow, red, green, and cyan circles indicate the location of the analysed conspicuous vortex flow and of the smaller swirls indicated in Fig. 1.