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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