[BAA-ebulletin 00894] Nacreous clouds

[BAA electronic bulletins service]

Nacreous clouds were seen from Cambridge this evening.  This type of cloud is 
fundamental to the creation of the ozone hole over Antarctica and is rarely 
seen from the UK.  The clouds form over the polar regions at heights of 
around 10 to 20km.  They are usually visible during civil twilight - the denser 
cloud has beautiful pearly coloured margins and is quite bright, but there is 
also a diffuse component that appears like stratocumulus cloud, but is much 
higher.

This winter has seen an unusually cold Arctic stratosphere, and over the last 
couple of days the "polar vortex" with the coldest air has become very 
elongated and has reached down to the UK.  There is a small chance that the 
clouds might again be visible before sunrise on February 2, but after that the 
area of cold air moves away from the UK.

Jonathan Shanklin
BAS Fellow
British Antarctic Survey, Madingley Road, Cambridge CB3 0ET, England