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Circumhorizon Arc, Parhelic Circle and Circular Halo over Whiting, NewJersey on July 22, 2007.
Jet Stream The Jet Stream was moving quickly to the North over New Jersey that day.

Cloud Patterns

Cloud Patterns - An Upper High Pressure System brought cold Cirrus Clouds from the North,while warm Cumulus clouds came from the South.




Circumhorizontal Arc

Circumhorizon Arc Fragment - When I first saw this I thought  it was an iridescent cloud.

Circumhorizontal Arc

There are perfectly formed the Ice Crystals in the upper atmosphere. The Plate Crystals that are parallel to the ground refract the sunlight at a 46% angle. We see this beautiful result of these perfect crystals and alignment. Even on a hot July day, there is ice in the air.


Circumhorizontal Arc

The Cumulus clouds are moving quickly to the east, while the Cirrus are moving to the South.  The arc is playing hide and seek.




Circumhorizontal Arc

A wide angle view (27 mm focal length) reveals multiple pieces of the arc that are visible. Judging by the wide field of view a Circumhorizon Arc  would stretch among the separated  Cirrus clouds.

Circumhorizontal Arc

The Circumhorizon Arc dissipates.



Parahelic Circle and Circular Halo

The Circular Halo and Parhelic Circle become prominent.



46 Degree Halo Simulation
There was discussion that the Circumhorizon Arc may have been a rare 46 degree Halo. However, when a simulation was run for a 46 degree Halo, no Parhelic Circle would form, just a 22 degree Halo. As a Parhelic Circle  was visible, that rules out a 46 degree Halo.

Halo Simulation and Visibility Frequency

Circumhorizon Arc, Infralateral Arc, A Parhelic Circle and a Circular Halo.



The Sun was at 68 degrees elevation when the Circumhorizon Arc was imaged. The Sun was at 62 degrees elevation when the22 deg halo and parhelic circle were imaged. Hexagonal Plate Crystals most likely formed these Arcs, as per the simulation. HaloSim was run to produce this simulation.  The odds of  a Circumhorizon Arc forming are ~ once every ten years.
Parhelic Circles form ~4x per Year
Circular Halos form 100 x per Year.

The odds mentioned here are referenced from Germany, at ~50deg latitude.

The odds to see a CHA from New Jersey at 40 deg latitude , give a higher frequency, as the Sun reaches a higher altitude, and spends much more time at the higher altitude then in Germany. The frequency currently is unknown to me, however I have seen them on 5 separate occasions over the past 2 years, since I have begun to look for them.


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Earth Science Picture of the Day has a wonderful photo of the Circumhorizon Arc as well, taken from Pilesgrove NJ.

A special Thanks to Les Cowley (Atmospheric Optics) for his work on determining the phenomena in play.