© George Anderson
Wokingham, England, United Kingdom of Great Britain and Northern Ireland
Latitude: 51° 25' 4'' N
Longitude: 0° 51' 48'' W
12 April 2015 0736 (Local Time)
Camera direction: towards NE
Image I.D.: P.1.15
CL = 0, CM = 0, CH = 1
Links in the image description will highlight features on the image. Mouse over the features for more detail.
Persistent aircraft condensation trails (contrails) cross the sky over southern England. These are classified as Cirrus homogenitus.
This picture shows Cirrostratus fibratus and Cirrus spissatus cloud, together with some aircraft condensation trails, Cirrus homogenitus at 3, 4. However, there are also two photometeors of particular interest:
Firstly there 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 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°, the azimuth of the parhelion 034° (an azimuthal distance of 120° from the sun).
The second photometeor is a white band which passes through the 120° parhelion; this is the parhelic circle. The parhelic circle circle is a white horizontal band circling the sky at 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 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.
Persistent aircraft condensation trails at 1, 2 (contrails) cover much of the sky in this picture. These contrails are classified as Cirrus homogenitus. The name homogenitus is used where the cloud has developed as a consequence of human activity. Because new, or recently formed contrails may display a variety of transient shapes, no species, varieties or supplementary features are used in the classification.
Some of the oldest contrails can be seen to have spread out over time. These clouds have lost their original linear appearance and have transformed, or mutated into cloud taking on the appearance of more natural looking Cirrus. This cloud is Cirrus homomutatus at 3, 4.
In this picture there are several aircraft condensation trails (Contrails) at 1, 2 and 3 across the sky. These are classified as Cirrus homogenitus. Near the horizon there is Cirrus and Cirrostratus fibratus. A sun pillar rises vertically above the Sun; formed by the reflection of sunlight by ice crystals in the Cirrostratus. The contrail across mid picture is spreading out to form Cirrus fibratus homomutatus and the cloud at the top of the picture has completely transitioned to Cirrus homomutatus, having almost lost any resemblance to its previous linear shape as a contrail.
Aircraft condensation trails (contrails) in the sky over southern England. Persistent contrails are classified as Cirrus homogenitus.
All the cloud in this image is man-made (anthropogenic). There are several aircraft condensation trails (Contrails), at 1, 2, 3, 4 and 5; these are classified as Cirrus homogenitus. In addition, cloud has spread out from older contrails to form wider areas of Cirrus that resembles naturally formed cloud. However, because it is known that this Cirrus mutated and developed from cloud of man-made origin (the original contrails), it is classed as Cirrus homomutatus.
There are at least two levels of the Cirrus cloud (duplicatus) in which there are largely straight cloud filaments (fibratus). Towards the top left, filaments appear vertically orientated in the picture at 7 and 8. Towards the bottom there is thicker Cirrus in which the fibratus filaments stretch more horizontally across the picture. The full cloud classification is therefore Cirrus fibratus duplicatus homomutatus.
Cirrus homogenitus (aircraft condensation trails; contrails) at an altitude of 6 Km, viewed from another aircraft.
(NB. Hour of day estimated)
Three condensation trails at 1, 2, 3 can be seen. They expand with time. The two older trails at 1, 2. probably made 15-30 minutes before the picture was taken, have assumed a fleecy aspect, while the most recent one, which is just being produced, merely looks like a white streak in the sky. Numerous Cirrus clouds can also be seen; they may have developed out of contrails formed earlier. A weak trough associated with a low near Iceland was passing over southern England. Rather humid and warm air, associated with a weak warm front at about 700 km distance, was invading the higher layers of the troposphere from the north-west.