Evolution of the Θ (latitude, solid line) and Φ (longitude, dashed line) components of the field lines n° 16 (cyan) and 20 (yellow) at 2 R_⊙ (top). Tangential velocity of the field lines n° 16 (cyan) and 20 (yellow) calculated at 2 R_⊙ between t = 17.75 τ and t = 29.25 τ (bottom). The cyan and yellow dashed lines display the tangential plasma velocities at 2 R_⊙ at the location of the footpoints of the associated field lines. The vertical dashed back line indicates the end of the large, rather straight slipping motion for the cyan field line (n° 16) and the beginning of the oscillations.