© Stephen Burt
Tregavethan, Truro, Cornwall TR4 9EL, United Kingdom of Great Britain and Northern Ireland
Latitude: 50° 16' 54'' N
Longitude: 5° 6' 59'' W
06 August 2009 1919 (Local Time)
Camera direction: towards NE
Image P/S code: P.1.9
Image I.D.: 4846
CL = 0, CM = 0, CH = 2
This image shows Cirrocumulus floccus developing into Cirrus uncinus, which is, in parts, merging into Cirrus spissatus. There are also a few elements of Cirrus floccus present. The Cirrus uncinus and spissatus are of the variety radiatus as strong south-south-west winds have arranged the Cirrus into parallel bands that appear to be converging at a point on the horizon.
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South-west England, UK lay under a ridge from the Azores anticyclone, while a fairly active waving front lay over southern England. Extensive high cloud associated with the frontal system persisted throughout the day to the east and north-east of Cornwall, UK.
The ascent from nearby Camborne, England, UK (15 km south-west of the site where the photograph was taken) from 1200 UTC shows very moist conditions at Cirrus levels, above a strong anticyclonic inversion at about 825 hPa. The winds at Cirrus levels were very strong south-south-west winds at close to 100 kt – very high for midsummer.
The satellite image from six hours earlier shows the thicker frontal cloud over Cornwall, UK (where a few spots of rain fell late that morning), with the bands of Cirrus spissatus lying at that time to the west of Cornwall.
The photograph shows a fine display of Cirrus that includes species fibratus and uncinus, both of the variety radiatus where, due to perspective, parallel bands appear to converge towards one point. Altocumulus in thin patches and Cumulus humilis (5 and 6) are also present.
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Cirrus fibratus radiatus and Cumulis humilis
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(NB. Time of day estimated; early afternoon)
The Cirrus elements have a variety of shapes in this view. Cirrus uncinus at 1 shows the filaments terminating in hooks and tufts. Other portions of the cloud field have small patches and streaks which appear to converge toward the horizon in the lower left of the picture. The Cirrus is progressively invading the sky; no Cirrostratus is apparent, however; thus the coding is CH = 4. The location was under a strong (70 m S-1) westerly jet. At low levels, a ridge axis was nearby, with cool NW winds to the east and a dry, southerly return flow to the west.
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