Jakarta –
The dark skies of the Arctic Circle were recently lit up with awe-inspiring colorful lights. Interestingly, this jaw-dropping spectacle is caused not by auroras, but by clouds of tiny ice crystals that drift higher in the atmosphere than usual.
The clouds, known as polar stratospheric clouds (PSC), only form when the lower stratosphere reaches temperatures below minus 81 degrees Celsius.
Usually, clouds don’t form in the stratosphere because it is too dry. But at this extremely low temperature, water molecules that are very far apart begin to coalesce into tiny ice crystals that form clouds.
This means, as quoted from Live SciencePSCs can form much higher than normal clouds, between 15 and 25 kilometers above the ground.
As sunlight shines through this crystal cloud, it is scattered, creating many different wavelengths of light, which has inspired the PSC’s nickname, ‘rainbow cloud’. Because of the cloud’s extreme height, Sunlight can hit the crystal and spread over the observer even when the Sun is off the horizon, which is when the cloud appears brightest.
On January 25, as rainbow clouds were visible, extreme freezing conditions in the stratosphere allowed PSCs to appear in the Arctic Circle, including Iceland, Norway and Finland.
Amateur photographer Jónína Guðrún Óskarsdóttir captured this stunning view from clear clouds over the top of Mount Jökultindur in Iceland. Another photographer, Fredrik Broms also captured this colorful sky phenomenon over Kvaløya near Tromsø in Norway.
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PSC shines through a gap in the clouds over Kvaløya in Norway on January 25. Photo: Fredrik Broms /northernlightsphotography.no
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Two types of PSCs
There are two types of PSC. Type I, which is made of a mixture of ice crystals and nitric acid, which produces a less spectacular color and may be related to the formation of the ozone hole. Type II, polar stratospheric clouds consisting of pure ice crystals and producing more vivid colors.
What is enshrined in this event is Type II. Type II PSC is often referred to as nacreous cloud because its iridescent hue sometimes resembles nacre, also known as mother of pearl, which is produced in the shells of some mollusks. However, their occurrence is extremely rare, much rarer than Type I clouds.
Type II clouds usually occur no more than two or three times a year over the Arctic, usually during the winter months. However, experts believe that both types of PSC could occur more frequently in the future as climate change creates more extreme weather, which could have an indirect impact on the ozone layer if more Type I clouds form.
Because of their intense color, nacreous clouds are often confused with the northern lights or aurora borealis at the North Pole. This more common phenomenon occurs when high-energy particles emitted by the Sun move down the magnetic field lines of Earth’s magnetosphere.
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