Parhelic Circle ray paths Atmospheric Halos, description and simulation. TOP Ex ternal and internal reflections make the parhelic circle. External reflections contribute most near to the sun. Rays reflected once inside the crystals produce much of the halo intensity. Opposite the sun, rays internally reflected twice or even more add their brightness.
Relative contributions depend on solar altitude and the crystal thickness.
Horizontal plate crystals, singly oriented columns and Parry oriented columns can all form parhelic circles. The simplest way is by a single external reflection but there are many others, some with the most intricate of ray paths. External reflection Rays reflect off any near-vertical face. Most effective when rays graze the surface. A route through side faces only.