G. Tsiropoula, I. Kontogiannis, E. Scullion

Vortex flows have been extensively observed over a large range of spatial and temporal scales in different lines and hence layers of the solar atmosphere and widely found in numerical simulations. However, they have never been reported so far in observations in the Hα line centre. High spatial and temporal resolution observations obtained with the CRISP instrument at the Swedish 1-m Solar Telescope in several wavelengths along the Ηα and Ca II 8542 Å line profiles reveal the existence of a persistent 1.7-hours small-scale vortex flow in contrast to short-lived such structures reported so far in literature. We discuss the appearance, characteristics, structure and dynamics of this vortex flow in these two lines as well as in simultaneous UV and EUV SDO/AIA channels and HMI magnetograms. Our analysis includes visual inspection and comparison of simultaneous or near-simultaneous observations in the different spectral lines and channels, study of Doppler velocities derived from the Ηα line profiles and detailed investigation of the vortex appearance, characteristics and dynamics using time slices along linear and circular slits. It reveals the existence of a funnel-like expanding structure with height that is possibly rotating rigidly or quasi-rigidly and exhibits significant substructure within it, manifested as several individual intermittent chromospheric swirls with typical sizes and durations. We further investigate oscillations within the vortex area using a wavelet analysis, phase differences using a cross-wavelet analysis and search for signatures of waves. We also discuss the possible generating physical mechanisms behind this unusual persistent vortex flow and try to understand its relation to previously reported short-duration small-scale magnetic swirls.