circumzenithal arc


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circumzenithal arc

[¦sər·kəm¦zē·nə·thəl ′ärk]
(optics)
A brilliant rainbow-colored arc of about a quarter of a circle with its center at the zenith and about 46° above the sun, produced by refraction and dispersion of the sun's light striking the top of prismatic ice crystals in the atmosphere, and usually lasting only a few minutes.
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References in periodicals archive ?
This leads me to believe that it is indeed a circumzenithal arc captured in the image, an optical effect formed as light refracts off ice particles in thin cloud at high levels.
Unlike a rainbow, which appears opposite the sun, a circumzenithal arc is centred around the zenith of the sky, and can only appear if the solar angle is less than 32 degrees.
For example, if you see a sundog or a circumzenithal arc, you'll know that the cloud has plate crystals aligned with their large hexagonal faces almost horizontally.
We call them pseudo-circumzenithal arcs, or PCZAs, because the ray paths are similar to those that form the beautiful, rainbowlike circumzenithal arcs on Earth.
Today, it's true, we seldom hear the circumzenithal arc described as being "of Bravais," or a well-developed fogbow referred to as "Ulloa's ring.
Using only a point-and-shoot camera he was able to capture a richly colored segment of the circumzenithal arc that appeared about 65 [degrees] above the Sun (see page 103).
Like its more common cousin the circumzenithal arc, this display is formed by refraction of sunlight in ice crystals of cirrus and high haze, which can be present year around.
Unlike rainbows, where sunlight refracts through raindrops, circumzenithal arcs occur when sunlight refracts through ice crystals in cirrus clouds.
When was the last time you glanced up on a sunny day to check for rings around the Sun, or any colorful circumzenithal arcs or iridescent clouds?