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Ice Crystals > Halos > Parhelic Circle > Parhelic Circle

Parhelic Circle

The parhelic circle belongs to the less common halos and is very rarely complete. It crosses the Sun (or the Moon), the 120° parhelia, and the anthelion. All these halos are white since they are caused by reflection (strictly speaking, refraction does occur because many ray paths are inside the crystals - however, there is no net refraction because the entrance and exit ray paths counter each other).

Both plate crystals and columnar crystals can form the parhelic circle. There may be a bluish or greenish tone about 10° - 15° behind the 120° parhelia  (‘blue spot’) where internal reflection is no longer total.

The parhelic circle very often shows reddish or deep violet fringes due to diffraction which have nothing to do with the halo itself. They should be present in every halo but are washed out by the brighter colours. The fringes are similar to a corona and are produced by very small ice crystals too small to produce clean halos - or supercooled water droplets. These crystals or droplets are not always present

Simulation of the parhelic circle (fisheye view) at a solar elevation of 22° with an extremely high crystal concentration. The simulation also shows the 120° parhelia, the circumzenithal arc, the 22° halo with its parhelia and the 46° halo.
Simulation with HaloSim 3.6 by © Les Cowley and Mike Schroeder shown with permission.

Close-up view of the region behind the 120° parhelion.
Simulation with HaloSim 3.6 by © Les Cowley and Mike Schroeder shown with permission.