Skies in the Arctic have been lit up by extremely rare "rainbow clouds" for more than three days. According to a report by LiveScience on Thursday (Dec 21), experts said these rainbow clouds, also known as polar stratospheric clouds (PSCs), could appear during the next few months.

Skies in the Arctic have been lit up by extremely rare "rainbow clouds" for more than three days. According to a report by LiveScience on Thursday (Dec 21), experts said these rainbow clouds, also known as polar stratospheric clouds (PSCs), could appear during the next few months. PSCs were spotted in Norway, Sweden, Finland, and Alaska, and even as far as Scotland. These colourful treats started appearing on Dec 18 due to an unusual cold snap and continued to appear till Dec 20. The report said that some smaller distinct clouds were also seen on Thursday, but in general, they seemed to be disappearing. 'The colours are spectacular' The photographs of PSCs above Gran in Norway were captured by Ramunė Šapailaitė. Speaking to Spaceweather.com, Šapailaitė called the colours seen in the sky "spectacular." She added, "The clouds were visible in the sky all day, but the colours really exploded just before sunset." Also read: It's holiday season in space too! See the beautiful running-chicken-like nebula The photographs, which Šapailaitė clicked on her phone, revealed the rainbow hues of PSCs and their iridescent shimmer. What are PSCs? According to Harvard University, PSCs are clouds that form when water vapour enters the stratosphere and temperatures are cold enough for water vapour to condense there. During the winter season, high latitudes receive very little to no solar radiation, so temperatures drop significantly during this period, known as polar night. Under these conditions, PSCs can develop, Harvard said. "They trap outgoing longwave radiation (OLR) and emit some of it back towards the Earth's surface, so they hinder atmospheric cooling," as per the university's website. The National Aeronautics and Space Administration (NASA) has said that PSCs are occurring with an increasing frequency in the Arctic. There are two types of PSCs- first: the ones made from a mix of ice crystals and nitric acid, which produce less spectacular colours and second: the ones which are composed of pure ice crystals and produce more vivid colors. The rainbow clouds that were seen in the Arctic on Dec 18 were type 2 PSCs.

Arctic skies lit up by extremely rare rainbow clouds. What's the phenomenon?

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Arctic skies lit up by extremely rare rainbow clouds. What's the phenomenon?