Schematic drawing of a magnetic Ω loop (shaded area) emerging above the solar photosphere. Upper panel: initial phase producing the linear polarization signature. Lower panel: the following phase, with the loop standing above the photosphere, producing the two circular polarization signatures. The location of the photospheric layer is marked by the average τ ₅₀₀ = 1 level. The upper photosphere layers are marked by the average τ ₅₀₀ = 0.1 and 0.01 levels (dotted horizontal lines). The dashed vertical lines show three LOS examples crossing the loop structure at different instants and locations. The arrows crossing the LOS represent the direction of the magnetic field vector.