Intensity distribution of the parhelic circle and embedded parhelia at low solar elevations: theory and experiments

We describe the intensity distribution of the parhelic circle for plate-oriented hexagonal ice crystals at very low solar elevations using geometrical optics. An experimental as well as theoretical study of in-plane ray-paths provides details on the mechanism for several halos, including the parhelia, the $120^{\circ}$ parhelia, the blue spot and the Liljequist parhelia. Azimuthal coordinates for associated characteristic features in the intensity distribution are compared to data obtained using a rotating hexagonal glass prism.