Time–distance diagram of (a) the swirling strength λ and of the vertical component of the following quantities: (b) swirling vector λ_z, (c) magnetic swirling vector , (d) partial derivative of the swirling vector ∂λ_z/∂t, (e) advection term , (f) stretching term , (g) hydrodynamical baroclinic term , (h) magnetic baroclinic term , (i) sum of baroclinic terms , and (j) magnetic tension term . The black dashed contours correspond to the λ_z = −0.1 Hz contours, which highlight the propagation of the Alfvén pulse. All plots are relative to the swirl event shown in Fig. 4 and are derived from a fixed, one pixel wide vertical slit through the center of that swirl.