Axial cut through the loop at y = 4 Mm. From left to right: Velocity transverse to the guide field (color, the red arrows illustrate the velocity field projected onto the plane of the axial cut), swirling strength computed after smoothing the velocity field with a Gaussian with an FWHM of 500 km, and axial component of the Poynting flux averaged over a slab between y = 3.5 Mm and y = 5 Mm centered on the swirling structure. An arclength of s = 15 Mm corresponds to a height above the optical surface of roughly h = 12.9 Mm. See Sect. 3.1 for a discussion.