|Polar Stratospheric Clouds by P-M Hedén (Clear Skies) 28 Dec '08.
"I was up in the Swedish mountains (Tänndalen) and witnessed the most intense nacreous cloud storm I´ve ever seen! I saw these 'clouds' from early morning to darkness and maybe even caught them 'at night". The clouds could be nacreous clouds (Type II Polar Stratospheric Clouds of ice crystals) embedded in less iridescent Type I PSCs of nitric and sulfur acid compounds. The gravity wave structure is characteristic of PSCs. Images ©P-M Hedén..