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A circumhorizontal arc is an optical phenomenon - an ice-halo formed by plate shaped ice crystals in high level cirrus clouds.The current accepted names are circumhorizon arc or lower symmetric 46° plate arc.[1] The complete halo is a huge, multi-coloured band running parallel to the horizon with its center beneath the sun. The distance below the sun is twice as far as the common 22-degree halo. Red is the uppermost colour. Often, when the halo forming cloud is small or patchy, only fragments of the arc are seen.
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