Beautiful 'mother of pearl' Nacreous clouds illuminate the Arctic

Due to a rare phenomenon called Nacreous, colourful skies have been visible over regions across the Arctic -- in Sweden, Norway and Finland for the past few days. Reportedly, this phenomenon even though beautiful to look at, also harbours danger in its chemical composition. Nacreous is also known as 'mother of pearl' and occurs because of rare atmospheric changes.  

How do the colours in the sky form? 

In Nacreous, the skies remain illuminated after the sun has set. This happens as polar stratospheric clouds catch the peachy sunlight long after it has abandoned the ground at up to 80,000 feet altitude.

Read: 'Process behind ice formation in clouds decoded'

These colours are sometimes spread across twice the height at which commercial aeroplanes fly. The ice crystals formed in the clouds, diffract the light and thus produce a colour pattern similar to that in a tilting compact disc.  

Look at the Nacreous images shared on social media here: 

How can these colourful skies be harmful 

The reaction between chlorine nitrate, hydrochloric acid and some polar stratospheric clouds can result in the production of chlorine atoms through various processes. 

These atoms can potentially act as a catalyst to destroy the ozone layer. However, it is unclear whether the Arctic clouds photographed over the last few days are the type of polar stratospheric clouds that can destroy the ozone. 

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