July - lightning You are here: Home Photo gallery Atmospheric optics Ice crystal halos Parry arcs

There are several types of Parry arcs. The most common are the upper sunvex and suncave Parry arcs, referring to their shape - convex or concave towards the sun. The photos below show the upper suncave Parry arc. It is a variation of the standard upper tangent arc, and is also caused by horizontally oriented pencil-shaped ice crystals, but these do not have a freedom of rotation along their long horizontal axis - one of the side crystal faces must be parallel to the horizon. The upper suncave Parry arc shows as a second upper tangent arc, just over the normal tangent arc. (The upper sunvex Parry arc would appear between the suncave arc and the upper tangent arc as a small V shape). Lower Parry arcs are also possibe.

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