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   Pyramidal upper parhelion 

Lone Arc. This bright and colourful arc was the only halo apparent in the sky ~ Norfolk, England 5th July 2000, 16.55 - 17.35 UT sun 28-22� high. The image, however, also shows a faint circular halo beneath the arc. Image �2000 Les Cowley.

Pyramidal 23� upper parhelion or Parry arc? The HaloSim simulation includes pyramidal crystals and Parry oriented columns. Both arcs are similar but the 23� parhelion best matches the photographs and visual appearance. The very faint circular arc could be a 23 or 22� halo. Thanks to Walter Tape and Jarmo Moilanen for help with the identification.
  Ray path for 23� upper parhelion. The crystal is oriented with its large pyramidal end pointing downwards. Rays enter the near horizontal top face and leave through one of the lower pyramidal faces. The path is very 'efficient' and generates a bright arc which survives quite large crystal tilts from vertical.