Rotation periods (below 500 s) derived for the Hα Doppler velocity time-series (panel a) and intensity time-series at Hα line centre (panel b), Hα − 0.26 Å (panel c), Ca II 8542 Å line centre (panel d), and Ca II − 0.055 Å (panel e) for the second observing period (08:28 UT–09:16 UT) as a function of angle and for different values of radius r from the approximate centre of the vortex flow (the respective colours are indicated in the top panel). Radii extend only up to 2″ for Hα, and for Ca II 8542 Å are limited up to 1″ because only the central swirl and within this radius is visible in this line (see Sect. 3). Angles are measured in a clockwise direction starting from position 0, which is clearly marked in Fig. 1 to the right of the vortex flow. All curves have been smoothed with a running average corresponding to ∼20° to remove spurious spikes. Grey-shaded areas indicate angles where the vortex flow is mostly affected by the dynamics of nearby fibril-like flows.