This was taken from the Age yesterday. It's called a nacreous cloud and like the circumhorizontal arc, very rare but unlike the equally beautiful arc, this is more deadly.
According to Andrew Klekociuk, an atmospheric physicist with the AAD, nacreous clouds are a catalyst that convert chlorofluorocarbons, changing them into forms that can destroy ozone in the presence of sunlight. Nacreous means "mother-of-pearl like".
The clouds form about 20 kilometres up and only when the mercury falls below minus 80 degrees. Weather balloons sent up to the clouds recorded temperatures of minus 87 degrees.
The photographer was Renae Baker, a Bureau of Meteorology officer based at Mawson. At those temperatures I'm happy to just look at her photographs.