© Frank Le Blancq
St Brelade, Jersey
Latitude: 49° 10' 12'' N
Longitude: 2° 10' 9'' W
22 June 2015 1954 (Local Time)
Camera direction: towards E
Image P/S code: P.1.4
Image I.D.: 4718
CL = 0, CM = 0, CH = 2
Dense patches of Cirrus spissatus following the passage of a surface cold front. The patches are aligned transverse to the upper level winds and also show signs of convective development, suggesting instability at their level. This is confirmed by a distinctive patch of Cirrus floccus with trails and Cirrus floccus in the initial stage of development. Some indistinctive mamma completes the story.
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Very high moisture from 4 000 to 7 500 m
This picture shows Cirrostratus fibratus and Cirrus spissatus clouds, together with some aircraft condensation trails (Cirrus homogenitus) at 3 and 4. However, there are also two photometeors of particular interest.
The first is the bright spot near the centre of the photograph; this is a 120° parhelion, caused by at least two internal ice crystal reflections of sunlight. Rays entering the top face of plate crystals reflect internally off two adjacent side faces and then exit through the lower face. The second 120° parhelion was not visible on this occasion. At the time of the photograph, the Sun’s azimuth was 274° and the azimuth of the parhelion was 034° (an azimuthal distance of 120° from the Sun).
The second photometeor is a white band which passes through the 120° parhelion; this is a parhelic circle. The parhelic circle is a white horizontal band circling the sky at the same angular elevation above the horizon as the Sun. The vertical faces of many ice crystals each mirror the Sun around the sky to form the circle. Only part of the circle was visible on this day. The elevation of the horizontal band was 020° above the horizon. At the time of these phenomena, a bright circumhorizontal arc was also visible but is not shown in this photograph.
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The image shows Cirrus cloud in dense patches typical of the variety spissatus at 1 and 2.
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Notable features in this image are the partial 22° halo occurring in a Cirrus spissatus and a Cirrus fibratus. The Cirrus spissatus is starting to thicken, but is not yet thick enough to appear greyish when viewed towards the Sun. Filaments of the fibratus are irregularly curved or nearly straight; are white; and have more of a silky sheen than a fibrous (hair-like) appearance. Several contrails can also be seen at 5 and 6.
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This photo shows extensive and beautiful sheaves of dense Cirrus (species spissatus) originating from a weak and decaying warm front.
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These patches of Cirrus are very dense, and are therefore of the species spissatus. From below the patches at 1 and 2, there is a little virga trailing back in the lighter winds below the Cirrus level. The top of a Cumulus congestus, unrelated to the Cirrus, is visible at 3.
A stationary front was lying NW-SE about 300 km to the north-east, with an anticyclone building to the south-west.
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This Cumulonimbus cloud has been almost completely converted from its earlier water-droplet form to an ice cloud. The fibrous upper part at 1 extends nearly to the base of the visible cloud, where a small area of updraught is visible at 2. Virga is nearly reaching the ground at 3 in this dry atmosphere. The region was under the influence of dry lower levels and strong diurnal heating in the afternoon.
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