Sun Halos, Sun Dogs & Circumzenithal Arcs In The Sky Today Thanks To Sandy!

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A rather stunning sight occurred over the Tennessee Valley today, thanks in part to high cirrus clouds that have been moving into the area on the backside of Post-Tropical Cyclone Sandy. Cirrus clouds are made up of millions of hexagonal ice crystals that refract the sunlight causing a 22 degree halo around the sun.  Something even more rare than a sun halo, is a circumzenithal arc which is also an optical phenomenon that occurs when ice crystals refract sunlight in high clouds, but the ice crystals have to be horizontally oriented. When this occurs it forms no more than one quarter of a circle that is on the zenith and on the same side as the sun. Sun dogs are basically the same thing as circumzenithal arcs, but not on the zenith.  Also people have viewed tangent arcs that touch the 22 degree halo above and below the sun.  Tangent arcs are caused by well developed columnar ice crystals in cirrus clouds drifting with their long axes almost horizontal. All four optical phenomenons have been seen today, which is a pretty rare event to see all three at one time!  Check out some of the photos sent in from viewers. Below is one sent in from Misty of Toney, where you can see the halo around the sun, the two sun dogs on either side and an upper tangent arc.

Optical phenomenons caused by ice crystals like moon/sun halos, sun dogs, tangent arcs and circumzenithal arcs can be seen year round, but are more common during the colder months, thanks to the transition of seasons and cold Arctic air moving in as the jet stream moves south. So on a sunny day with thin clouds, make sure to look up at the sky, you never know…you may see stunning images like the ones captured today!

- Jennifer Watson

Twitter: @JWatson_Wx

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