Optical effects in the atmosphere

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Okologorizontalnaya arc or a fiery rainbow — one of the halo species, a unique optical effect in the atmosphere, which is the appearance of a horizontal rainbow, against a background of light, high-lying cirrus clouds.

The phenomenon manifests itself under certain conditions:

- The sun should be above 58 degrees above the horizon;

- there must be cirrus clouds in the sky;

- Flat hexagonal ice crystals in the clouds should be placed horizontally.

North of 55 °. from. w. and south of 55 °. Yu. w. the phenomenon can not be observed (from the surface of the earth), since the sun does not rise there so high (however this can be compensated by climbing the mountain [1]). The arc appears when the sun rises at least 57.8 °. (90 ° min 32.2 °) above the horizon, the brightness peak is at 67.9 °.

The rarity of the phenomenon is explained by the fact that ice crystals in the cloud should be oriented horizontally for refraction of solar beams. The rays enter through the vertical side wall of a flat hexagonal crystal, pass through it and come out from the lower horizontal side. Such a scheme provides a spectral separation of colors that, like a rainbow, & lighten & raquo; cirrus cloud.

Fire Rainbow