© Frank Le Blancq
Portelet, St Brelade, Jersey
Latitude: 49° 10' 33'' N
Longitude: 2° 10' 27'' W
19 June 2013 2027 (Local Time)
Camera direction: towards N
Image I.D.: P.7.18
CL = 5, CM = /, CH = /
Links in the image description will highlight features on the image. Mouse over the features for more detail.
The Stratocumulus stratiformis in this image (reported height 3000ft at nearby synoptic station Jersey Airport) shows various shades of grey often typical of Stratocumulus. The cloud mass was sufficiently opaque to mask the sun which identifies it as belonging to the variety opacus. Of most interest is the dramatic looking and highly exaggerated undulation reminiscent of a breaking wave which identifies it as the supplementary feature asperitas. Asperitas is more chaotic than undulatus, with less horizontal organisation and is in general characterised by waves in the cloud base which resemble a roughened sea surface seen from below. Variations in levels of illumination and cloud thickness can lead to dramatic visual effects. The dramatic feature in this photograph was visible for over 20 minutes with little change in structure and no detectable change in surface conditions as the cloud slowly drifted by.
A shallow low of 1010 hPa was drifting west in the Bay of Biscay with a weak ridge building over Ireland. A weak north-easterly air flow covered the photo location in the English Channel.
The sounding from Brest (WMO 07110) four hours after the photograph, was in the same air mass with similar temperature and dew point (allowing for nocturnal cooling). A moist boundary layer is evident to approximately 930 hPa, with a weak inversion of nearly 2°C at 975 hPa.
This image shows a grey, extended layer of Statocumulus with some dark parts of the species stratiformis. The cloud is thick enough to completely mask the sun and thus is variety opacus. The feature of most interest in this image is the well-defined wave-like structure (at, e.g., 2 and 3) on the underside of the cloud. The undulations are more exaggerated and less organised than found in variety undulatus, so are designated as supplementary feature asperitas. The waves may be smooth, as in this image, or dappled with smaller features and sometimes descend into sharp points as if viewing the sea surface from below. Variations in thickness and illumination of the cloud can lead to some dramatic visual effects. Nearby observations show the cloud base lowered to between 4000 and 5000ft around the time of the photograph, with showers and thunderstorms recorded to the northeast and northwest.
This image shows a grey, extended layer of Statocumulus with some darker parts of the species stratiformis. It is sufficiently opaque that the sun would be completely masked and thus is variety opacus. Of special interest is the well-defined wave-like structure on the underside of the cloud, seen at 2 and 3. The undulations are more exaggerated and less organised than in variety undulatus and are designated supplementary feature asperitas. The waves may be smooth, or dappled with smaller features and sometimes descend into sharp points as if viewing the sea surface from below. Variations in the thickness and illumination of the cloud can lead to some dramatic visual effects. At the time of this image the measured cloud base of 1820m (about 6000ft) is at the top limit of the low cloud étage and could possibly be mistaken for Altocumulus.
The wave-like feature on the base of this Stratocumulus stratiformis opacus is the supplementary feature asperitas.