Phase differences between the Hα ± 0.26 Å and Hα LC pair within (a) the vortex flow area, the areas of swirls within the red, cyan, and green circles and the QSR and FSR areas depicted in Fig. 1 during the second observing time interval, i.e. 08:28 UT–09:16 UT (panels a–f) and (b) for the two swirls within the red and cyan circles for specific time intervals (denoted in the respective panels) when these swirls are clearly visible (panels g and h). Both wavelengths are mainly of chromospheric origin and their formation heights are separated by a few hundred kilometers (see Sect. 3). Filled contours represent the cross-power distribution, while white lines denote the position of maximum cross-power, normalised to unity for each frequency element as shown by the vertical bar. The black dashed contour indicates the 50% level from maximum cross-power, and provides a measure of the scatter as it represents the FWHM of the cross-power distribution at each frequency. Cross-power below 10% has been disregarded while all curves have been smoothed with a running average of seven frequency points to remove spurious spikes. The corresponding phase difference of the normalised-to-unity maximum-cross power as a function of frequency, within all considered areas and for the entire considered observing interval only, is also shown in a separate panel (panel i) for an easier and direct comparison.