Cloud iridescence

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Iridescent mid altitude clouds
Iridescent polar stratospheric cloud at sunset over Aberdeen, Scotland
Cloud iridescence, seen above the clouds covered with grey clouds, Pondicherry, India

Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in altocumulus,[1] cirrocumulus, lenticular,[2] and cirrus clouds.[3][4][5] They sometimes appear as bands parallel to the edge of the clouds. Iridescence is also seen in the much rarer polar stratospheric clouds, also called nacreous clouds.[6]

The colors are usually

convex mirror
or in a pool of water.

Etymology

Irisations are named after the Greek goddess Iris, goddess of rainbows and messenger of Zeus and Hera to the mortals below.[8]

Mechanism

Iridescent clouds are a

ice crystals individually scattering light. Larger ice crystals do not produce iridescence, but can cause halos, a different phenomenon.[9]

Irisation is caused by very uniform water droplets

interference effects[10] (beyond about 10 degrees from the Sun). It can extend up to 40 degrees from the Sun.[11]

If parts of clouds contain small water droplets or ice crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, while newly forming clouds produce the brightest and most colorful iridescence. When the particles in a thin cloud are very similar in size over a large extent, the iridescence takes on the structured form of a corona, a bright circular disk around the Sun or Moon surrounded by one or more colored rings.[9][12][13]

Gallery

  • Irisation in clouds over Wellington NZ
    Irisation in clouds over Wellington NZ
  • Irisation or iridescence in super-cooled cloud droplets in cirrocumulus clouds.
    Irisation or iridescence in super-cooled cloud droplets in
    cirrocumulus
    clouds.
  • Irisation in cirrus (or maybe cirrocumulus) clouds behind Stratocumulus (bottom), in the afternoon over Warsaw, Poland.
    Irisation in
    Stratocumulus
    (bottom), in the afternoon over Warsaw, Poland.
  • Vibrant cloud iridescence captured before sunset
    Vibrant cloud iridescence captured before sunset
  • Iridescent clouds seen in Tenerife
    Iridescent clouds seen in Tenerife
  • Parker Canyon, AZ. Aug 6th, 2022
    Parker Canyon, AZ. Aug 6th, 2022

See also

References

  1. doi:10.1080/00431672.1988.9930533
    .
  2. ^ Answers.com – Sci-Tech Dictionary: irisation
  3. ^ Nemiroff, R.; Bonnell, J., eds. (25 November 2007). "An Iridescent Cloud Over Colorado". Astronomy Picture of the Day. NASA.
  4. ^ "Iridescent Clouds". Atmospheric Optics.
  5. PMID 12570270
    .
  6. ^ "Nacreous Clouds". Atmospheric Optics.
  7. ^ PHOTOMETEORS, by Jesús Martínez-Frías Archived 2009-12-13 at the Wayback Machine
  8. ^ The Cloudspotter's Guide By Gavin Pretor-Pinney, p. 233
  9. ^ a b "Cloud Iridescence | SKYbrary Aviation Safety". skybrary.aero. Retrieved 2022-08-19.
  10. ^ Color and Light in Nature By David K. Lynch, William Charles Livingston, p. 133
  11. ^ PHOTOMETEORS, by Jesús Martínez-Frías Archived 2009-12-13 at the Wayback Machine
  12. ^ "Corona". Atmospheric Optics.
  13. PMID 22016246
    .

External links

Wikimedia Commons has media related to Iridescent clouds.
Look up iridescent cloud in Wiktionary, the free dictionary.


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