Temporal evolution of the vertical velocity v_z along the field line followed in Fig. 5 at the position of highest C iv (1548 Å) intensity. (1) and (2) indicate the two different field line configurations shown in Fig. 5, associated with different flow patterns along the field line. (1): Material is flowing upwards along the field line at the site of highest C iv (1548 Å) corresponding to an observed blueshift. (2): Material is flowing downwards along the field line at the site of highest C iv intensity corresponding to an observed redshift.