Nacreous Clouds or Polar Stratospheric
The word nacreous
comes from nacre the substance that forms
mother of pearl. The similarity here is
clear with the inner surface of a mollusc
shell such as an abalone for instance.
This kind of cloud is found mainly at
the poles, though more commonly in Antarctica
than the Arctic as Antarctica gets colder,
extreme cold is required for their formation.
They form in the stratosphere which is the
layer of atmosphere that starts at about
10,000m (6 miles) up and stretches on to
around 50,000m (31 miles). The stratosphere
comes a little closer to the surface towards
the poles reaching down to about 8,000m
Picture taken 23/08/2009
12.25 - McMurdo Antarctica.