Example of the detected magnetic swirls. The black-and-white background in panel a is the photospheric vertical magnetic field at frame 63. Blue (red) dots and curves are the centres and edges of the detected magnetic swirls with a anticlockwise (clockwise) rotation. The black-and-white background in panel b denotes the Γ₂ distribution obtained from the photospheric horizontal velocity field at frame 63. The red and blue contours in panel b represent the Γ₂ distribution obtained from the photospheric vertical magnetic field at levels of −2/π and 2/π, respectively.