Indicative images of the Doppler velocities derived from the Hα profiles as explained in Sect. 2. Negative and positive Doppler velocities indicate respectively upwards and downwards LOS motions. The yellow circle denotes the conspicuous vortex flow while red, green, cyan, and orange circles (see also Fig. 4) denote smaller observed swirls (see Sect. 3.2). The temporal evolution of Doppler velocity is shown in the right panel of the movie attached to Fig. 4.