© George Anderson
Wokingham, England, United Kingdom of Great Britain and Northern Ireland
Latitude: 51° 25' 4'' N
Longitude: 0° 51' 48'' W
08 November 2016 0926 (Local Time)
Camera direction: towards WSW
Image P/S code: S.4.16
Image I.D.: 5454
CL = 0, CM = 5, CH = 0
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Altocumulus stratiformis perlucidus translucidus cavum
This image shows two fallstreak holes (supplementary feature cavum) in a thin layer of Altocumulus (seen at 1 and 2). The holes are roughly circular in shape, but in this instance their edges appear somewhat ragged and indistinct. Over time, they have enlarged to the point where they have almost merged, with only a small area of cloud separating them. The central areas of ice crystals, or fallstreaks, are clearly visible in the centres of the holes at 4 and 5.
A series of fronts were approaching from the west and the Altocumulus was progressively invading the sky and generally thickening as a whole during the morning. At the time of the photograph, the extensive layer (stratiformis) had spaces between the cloud elements (perlucidus) and was sufficiently translucent to reveal the position of the Sun (translucidus). The full classification is therefore Altocumulus stratiformis perlucidus translucidus cavum.
These holes were just a few of many (at least 17) that were seen from the observer’s location during a two-hour period. The accompanying time-lapse sequence shows several holes drifting across the sky and the satellite image shows that fallstreak holes occurred widely in the thin layer of cloud as it moved eastwards over England, UK.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
© George AndersonWokingham, England, United Kingdom of Great Britain and Northern IrelandLatitude: 51° 25' 4'' NLongitude: 0° 51' 48'' W08 November 2016 0926 (Local Time)Camera direction: towards WSWCL = 0, CM = 5, CH = 0Image P/S code: S.4.16Image I.D.: 5454
A series of fronts were approaching from the west.
© Crown Copyright
The Metop-A image from 1010 UTC shows that several fallstreak holes had developed in the extensive sheet of Altocumulus.
© EUMETSAT, 2016
Altocumulus stratiformis perlucidus translucidus cavum
This thin, translucent and extensive layer of cloud is Altocumulus stratiformis translucidus. In the top part of the picture it also displays the variety perlucidus, as there are the gaps between the cloud elements. However, the most striking feature is the large, roughly circular hole beneath which there is virga. The large hole is the supplementary feature cavum, popularly known as a “fallstreak hole” or “hole-punch cloud”. The full classification for the cloud is therefore Altocumulus stratiformis perlucidus translucidus cavum.
Also of note is a linear gap in the cloud between the fallstreak hole and the horizon. This is an aircraft dissipation trail, or distrail, formed as a result of an aircraft flying through the cloud layer. Informally this is sometimes known as a “canal cloud”. It later transformed into a circular-type hole (see the accompanying time lapse).
The supplementary feature cavum is formed when glaciation occurs in a thin cloud layer consisting of supercooled water droplets that are in a liquid state and at a temperature below 0 °C. As the supercooled water drops glaciate, the resulting ice crystals fall from the cloud layer to a lower level as virga, or fallstreaks. The resulting cloud hole typically grows larger with time while the glaciation process continues.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
© Tsz Cheung LeeKwun Tong, Hong Kong, ChinaLatitude: 22° 18' 41'' NLongitude: 114° 13' 38'' E19 January 2015 0830 (Local Time)Camera direction: towards SWCL = 0, CM = 3, CH = 0Image P/S code: P.4.16Image I.D.: 5167