Taken by Hans-Dieter Fleger on December 27, 2016 at Telemark, Norway
On our 2.5 hour drive from Atrå to Porsgrunn (South Norway) we could observe beautiful and colorful Polar Stratospheric Clouds (PSCs) / Mother of Pearl Clouds all the way from start to finish. On some occasions the colors were extreamly intens and shining.
PSCs provide surfaces upon which heterogeneous chemical reactions take place. These reactions lead to the production of free radicals of chlorine in the stratosphere which directly destroy ozone molecules.
PSCs form poleward of about 60°S latitude in the altitude range 10 km to 25 km during the winter and early spring. The clouds are classified into Types I and II according to their particle size and formation temperature.
Type II clouds, also known as nacreous or mother-of-pearl clouds, are composed of ice crystals and form when temperatures are below the ice frost point (typically below -83°C).
The Type I PSCs are optically much thinner than the Type II clouds, and have a formation threshold temperature 5 to 8°C above the frost point. These clouds consist mainly of hydrated droplets of nitric acid and sulphuric acid.