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Brannenburg, Germany

Latitude: 47° 44' 20'' N

Longitude: 12° 5' 18'' E

31 December 2005 1439 (Local Time)
Camera direction: towards SW

Image P/S code: P.13.3

Image I.D.: 5624

C_L = 0, C_M = 3, C_H = 0

Irisation/iridescence
Iridescent colours cover a large part of this cloud layer. This is known as irisation.

The cloud is identified as a very high Altocumulus, almost bordering on Cirrocumulus. As the layer is relatively extensive, it is of the species stratiformis. It is also thin and translucent (variety translucidus) and there are undulations (variety undulatus).

Irisation results from the interaction of sunlight with small, uniformly sized cloud particles. Within about 10° from the Sun, diffraction is the main cause of irisation. Beyond about 10°, the interference of light waves is usually the predominant factor.

The colours green and pink tend to predominate, although other colours are seen, such as blue. They are often delicate, pastel shades, but can be brilliant.
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© Claudia Hinz
Brannenburg, Germany
Latitude: 47° 44' 20'' N
Longitude: 12° 5' 18'' E
31 December 2005 1439 (Local Time)

Camera direction: towards SW
C_L = 0, C_M = 3, C_H = 0
Image P/S code: P.13.3
Image I.D.: 5624
Irisation in Cirrocumulus lacunosus
The colours appearing in this Cirrocumulus cloud are due to irisation. Near to the Sun, irisation results when light waves are diffracted by very small, uniformly sized cloud particles. Beyond about 10° from the Sun, the interference of light waves is usually the dominant factor. Green and pink are the colours that typically predominate, although some blue is also visible here.

Note that the photograph has been deliberately underexposed in order to adequately record the delicate, pastel shades of colour. In reality, the scene here would be very bright – hence why the photographer has mostly blocked the intense direct sunlight with the roof of the building. Cirrocumulus is a white cloud without shading. The small holes at 6 and 7 indicate the cloud variety lacunosus.
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© Claudia Hinz
Mt. Wendelstein, Bavarian Alps, Germany
Latitude: 47° 42' 10'' N
Longitude: 12° 0' 44'' E
20 September 2007 1442 (Local Time)

Camera direction: towards SW
C_L = 0, C_M = 0, C_H = 9
Image P/S code: S.13.3 4
Image I.D.: 5625
Irisation/iridescence
Irisation or iridescent colours are seen in these lenticular (lens-shaped) clouds, high above the Bavarian Alps, Germany.

The iridescent colours are caused by the diffraction of light waves by very small, uniformly sized droplets or ice crystals that make up the cloud. Green and pink occur most often, and the colours are often in pastel shades. Iridescence appears on clouds in the same general direction as the Sun.
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© Claudia Hinz
Mount Wendelstein, Bavarian Alps, Germany
Latitude: 47° 42' 10'' N
Longitude: 12° 0' 44'' E
03 January 2012 1449 (Local Time)

Camera direction: towards SW
C_L = 0, C_M = 0, C_H = 9
Image P/S code: S.13.3 5
Image I.D.: 4839
Altocumulus stratiformis translucidus cavum
This image shows a well-developed fallstreak hole in Altocumulus stratiformis. The hole (cavum), filled with ice crystals, formed over a period of 40 minutes and eventually became very large (40° angle of view) as it was blown from the north-west to the south-east. Note that the image has been slightly underexposed deliberately in order to show the irisation or iridescence on the cloud edges, in contrast to which the (ice crystal) virga, or fallstreaks, show as pale grey in colour. An older hole, in which the fallstreaks appear to have evaporated, can be seen at the lower right. Another layer of cloud (duplicatus) can be seen at the lower left of the image. Some higher Cirrus is at the top left.

The Altocumulus formed ahead of a warm front advancing from the north-west around a very deep (for mid-summer – 985 hPa) cyclonic centre located over Denmark, in a cool north-westerly airstream.

The supplementary feature cavum is formed when glaciation occurs in a thin cloud layer consisting of supercooled water droplets in a liquid state at a temperature below 0 °C. As the supercooled water drops glaciate, the resulting ice crystals fall from the cloud layer to a lower level as virga, or fallstreaks. The resulting cloud hole typically grows larger with time as the glaciation process continues. The ice crystals may fall into drier air, where they evaporate, and so the hole may eventually lose its central fallstreaks.
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© Stephen Burt
Stratfield Mortimer, near Reading, England, United Kingdom of Great Britain and Northern Ireland
Latitude: 51° 22' 12'' N
Longitude: 1° 2' 24'' W
26 June 2007 1908 (Local Time)

Camera direction: towards W
C_L = 0, C_M = 3, C_H = 1
Image P/S code: S.4.16
Image I.D.: 4957
Cirrocumulus lenticularis with partial corona and irisation
The clouds in this image are characterized as Cirrocumulus due to their whiteness; the general absence of shading; and the presence of fine ripples and very small rounded elements. These patches have a broadly elongated lens shape (seen at 3 and 4) when seen in profile and reasonably well-defined outlines, as found in the species lenticularis. Behind the cloud, the diffraction of light from the Sun by tiny cloud droplets (or sometimes small ice crystals) is causing a partial corona. The pastel shades of irisation can also be seen on the lower lenticular cloud.
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© Yoshiaki Sato
Kiyose, Tokyo, Japan
Latitude: 35° 46' 34'' N
Longitude: 139° 31' 48'' E
03 January 2012 1223 (Local Time)

Camera direction: towards SE
C_L = 0, C_M = 0, C_H = 9
Image P/S code: S.2.2 35
Image I.D.: 5098
Cirrocumulus stratiformis with irisation
The main feature of this zoomed-in photograph is the area of irisation with pastel shaded colours. This colouration indicates the presence of small, uniformly sized, supercooled water droplets that can occur in Cirrocumulus cloud. It also helps the fine elements within the Cirrocumulus stratiformis cloud stand out.
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© Jarmo Koistinen
Kamppi, Helsinki, Finland
Latitude: 60° 10' 7'' N
Longitude: 24° 56' 7'' E
30 September 2015 1809 (Local Time)

Camera direction: towards SW
C_L = 0, C_M = 0, C_H = 9
Image P/S code: S.2.14.1
Image I.D.: 5105
Cirrocumulus stratiformis and lenticularis with irisation
The image shows irisation on Cirrocumulus cloud close to the Sun. Irisation is a form of light interference caused by small, uniformly sized, super-cooled water droplets in the cloud, which display pastel or mother-of-pearl shades, especially greens and pinks. This display lasted 30 minutes. The cloud overall displays small elements with an apparent width of less than 1° and ripples typical of Cirrocumulus. At first the cloud was small, consisting of lenticularis-like patches. It expanded rapidly into a layer of Cirrocumulus stratiformis and within 10 minutes covered 6/8 of the sky. Ceilometers recorded a steady cloud base at 6 400 m.
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© Jarmo Koistinen
Kamppi, Helsinki, Finland
Latitude: 60° 10' 11'' N
Longitude: 24° 56' 19'' E
30 September 2015 1808 (Local Time)

Camera direction: towards SW
C_L = 0, C_M = 0, C_H = 9
Image P/S code: S.2.14
Image I.D.: 5106

Irisation/iridescence

Irisation in Cirrocumulus lacunosus

Irisation/iridescence

Altocumulus stratiformis translucidus cavum

Cirrocumulus lenticularis with partial corona and irisation

Cirrocumulus stratiformis with irisation

Cirrocumulus stratiformis and lenticularis with irisation