Nacreous Clouds

From an old 1966 slide and from a set moved from the 'other' site. We were knocked over by those clouds behind the meteorological office. They are Nacreous Clouds, also known as "Mother of Pearl" clouds because of their colours or, more currently, as "Polar Stratospheric Clouds". They are made of ice crystals (which give their colour) and are about 20,000 metres high with temperatures dropping to about -80 C. They had always been considered quite rare and I believe our sighting was one of the first confirmed in Antarctica: there have been numerous sightings since.. Ozone depletion caused by chlorofluorocarbon gases has caused the polar stratosphere to become colder in spring (ozone keeps it warmer, so less ozone ie "the ozone hole" means lower temperatures) - yes, this is relevant to climate change. View on black. And HFF!