Observations from a quiet Sun region including network fields. The left panel shows the HMI magnetogram that was aligned with the IRIS observation. The gray scale in the HMI magnetogram is saturated at ±100 G but values up to ±1000 G are reached. Panels b–d show the observed intensity as brightness temperature T_b at the k₂ and k₃ features of the Mg II k line. The limits of the colorscale are not the same as in Fig. 2 in order to increase the contrast. The size bar in panel a indicates the size of the simulation domain. Green colored pixels indicate where no features could be found or no measurements are available.