Circumhorizontal arcs (pictured here) occur only between 55 degrees South and 55 degrees North, usually near the time of the respective summer solstice. They are formed by plate-shaped ice crystals in high level cirrus clouds. Other accepted names for circumhorizontal arcs are circumhorizon arc and lower symmetric 46° plate arc. Due to their large angular size they are rarely seen complete and most often appear as part of a cloud, as seen here on May 23, 2012 at 39°36'5"N, 74°20'17"W.
|May 23, 2012 39°36'5"N, 74°20'17"W (Click for full-size image)|