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.
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.