Indicative images of the ROI, almost co-temporal with respective Hα images of Fig. 4, at different wavelengths of the Ca II 8542 Å line. The yellow circle denotes the area of the conspicuous Hα vortex flow (e.g. Fig. 4g) while red, green, and orange circles denote smaller observed swirls also seen in Hα (see panels of Fig. 4) and discussed in Sect. 3.2. The white rectangle in panel f encloses the upflow event also seen in the extreme Hα blue wing (Fig. 4v).