Mean line profiles of a) Mg II k 2796 Å and b) subordinate Mg II 2798.8 Å lines in a subregion of the ROI, indicated with the strip in Fig. 6, at some specific times including the observations of the vortex edges by the IRIS slit (i.e., 08:12:42 UT and 08:14:23 UT for the first and second upflow event, respectively). The mean line profile (black dashed line) in the full FOV of the IRIS spectrograph excluding the vortex region is also shown at each panel as a reference.