© Jarmo Koistinen
Savonlinna, Finland
Latitude: 61° 52' 8'' N
Longitude: 28° 53' 24'' E
27 July 2008 0644 (Local Time)
Camera direction: towards NW
Image P/S code: P.2.6
Image I.D.: 5103
CL = 0, CM = 0, CH = 9
The image shows Cirrocumulus cloud at the zenith of the sky on an otherwise clear day. The cloud is a bright white without shading and is composed of small elements. It has an overall lens shape, indicative of the species lenticularis, with rather diffuse edges. The variety lacunosus with its fine-scale honeycomb structure can be seen in detail towards the top of the image. A sounding representative of the airstream suggests a cloud height of about 7 000 m.
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This zoomed-in image is of a section of Cirrocumulus cloud. It illustrates the typical structure of the variety lacunosus, with more or less regularly distributed round holes like a net or honeycomb.
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Low pressure of 993 hPa was present over the North Atlantic, with an anticyclone of 1028 hPa over northern Scandinavia. The photo was taken on the eastern flank of the anticyclone. A northerly flow was present in the upper atmosphere.
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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The image shows mainly Cirrocumulus cloud, identified by its very small elements with an apparent width of less than 1°. Two varieties can be seen: the undulations identify the variety undulatus, while the well-defined small holes that look like a net identify the variety lacunosus. To the lower right is the edge of a sheet of Cirrocumulus stratiformis, while to the left is some Cirrus fibratus.
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This extensive cloud sheet belongs, on account of its fineness and whiteness, to the genus Cirrocumulus. Small rounded elements without shading at 1, 2 and ripples at 3, 4 are visible almost everywhere. The lacunosus structure is evident from the numerous holes at 5, 6. As often occurs in Cirrocumulus, some Cirrus fibratus is merged with the patches. This sky was associated with an old cold front which passed over the area slowly from the north-east. The front caused a temporary increase of cloudiness but no precipitation.
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