|Wegener Arcs – Ice halos imaged by Peter Upton, Yukon, Canada June 18. ©Peter Upton, shown with permission.|
Wegener arcs form a cross on the parhelic circle opposite the sun. They are rare and when seen this bright even more so.
They skirt the zenith and meet the 22° and circumscribed halos tangentially. One of them can just be seen in the enhanced sunward view below.
Column ice crystals drifting with their long axes nearly horizontal produce them.
Their ray path is almost the same as that of the upper tangent or circumscribed arcs except that the ray reflects internally from a crystal end face.
Thus their rarity because the geometry is unfavourable and column end faces do not usually have the required optical perfection.