Illustration of mechanism causing strong asymmetries in the incident radiation Mg II K line profiles received by moving plasma. This example is for a radial velocity of 50 km s⁻¹ and altitude of 10 000 km. In the left panel are ten profiles corresponding to the solar-disc illumination from ten concentric-ring zones of Gunár et al. (2021). The profile with the largest shift from the static case (dashed lines) corresponds to the zone at the disc centre. The profile with the least Doppler shift corresponds to the zone at the limb. In the right panel is the averaged profile from all zones.