© 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
Image P/S code: S.2.14
Image I.D.: 5106
CL = 0, CM = 0, CH = 9
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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 KoistinenKamppi, Helsinki, FinlandLatitude: 60° 10' 11'' NLongitude: 24° 56' 19'' E30 September 2015 1808 (Local Time)Camera direction: towards SWCL = 0, CM = 0, CH = 9Image P/S code: S.2.14Image I.D.: 5106
The 300-hPa chart shows a region of fast flowing westerly winds (upper-level polar front) over southern Finland, north of a blocking high. The anticyclonic flow and dry air mass strongly suppressed cloud development.
© www.wetter3.de
The sounding was taken about 3 hours before and 100 km north-west of the image location. Wind speed at Cirrocumulus level was 75 kt from the north-west and the temperature was about –20 °C, with irisation indicating the presence of small, uniformly sized, supercooled water droplets.
© University of Wyoming
The simultaneous NOAA-15 image, a combination of channels 3, 4 and 5, reveals a small cluster of tiny upper cloud elements in the centre of the image, where the cloud photograph was taken.
© Finnish Meteorological Institute
Cirrocumulus lenticularis
Cirrocumulus species lenticularis, which appears in patches shaped like lenses or almonds. They are often very elongated and usually have well-defined outlines. The patches are mostly smooth and are very white throughout. This image overall shows distinct undulations, making it the variety undulatus. It also shows some small transverse ripples seen at times in Cirrocumulus cloud.
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© PascualSerra, Valencia, SpainLatitude: 39° 40' 55'' NLongitude: 0° 27' 35'' W18 March 2015 1506 (Local Time)Camera direction: towards NCL = 0, CM = 0, CH = 9Image P/S code: P.2.2Image I.D.: 4809
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 HinzBrannenburg, GermanyLatitude: 47° 44' 20'' NLongitude: 12° 5' 18'' E31 December 2005 1439 (Local Time)Camera direction: towards SWCL = 0, CM = 3, CH = 0Image P/S code: P.13.3Image I.D.: 5624