Development of Kelvin-Helmholtz vortices near the oscillating loops. Top: v_z velocity component and the corresponding velocity field streamlines in cuts parallel to the y − z plane at x = 13 Mm shown before the oscillation onset (left), during the oscillation (middle), and at the end of the oscillation (right). Bottom: same as above, but for oscillation 2. The red crosses correspond to the positions at which the individual loops in the bundle intersect the cut. The locations of the enhanced shear in the v_z velocity component correspond to strong counter-directional flows. In both cases, several vortices develop in the vicinity of oscillating structures.