Time slice diagrams in two slices marked in the H_α blue wing image at −0.8 Å (left panel). The right panels, from top to bottom, show the plasma trajectories moving along the S1 and S2 slices, respectively. S1 indicates the sweeping motion of the front of the jet and S2 the slipping motion of the bright footpoint of the jet, which ultimately invades the sunspot umbra. The footpoint of the jet moves by about 2.1 km s⁻¹ which is around 12° min⁻¹. The top of the jet moves with a speed of 6.9 km s⁻¹.