The Arctic Circle experienced an extraordinary phenomenon that illuminated the skies with rainbow clouds. Although they could be confused with the so-called aurora borealis, they are completely different phenomena, and instead, iridescent rainbows shone in broad daylight.
What Are Rainbow Clouds?
Known as polar stratospheric clouds (PSCs), they form in the layer of the atmosphere known as the lower stratosphere when it reaches a temperature below -81ºC. Normally, clouds do not form in the
stratosphere because it is too dry, but when it reaches unusually low temperatures, closely spaced water molecules begin to collapse and coalesce into tiny crystals. The result is clouded much higher than usual, which are between 15 and 25 kilometers high and are made up of millions of crystals that manage to refract sunlight.
As the sun’s rays rise in the sky, they gradually pass through the crystals, which act as a prism that breaks the light into all its colors. It is for this reason that they are called rainbow clouds, as they act similar to raindrops in forming a rainbow. In addition, the extreme altitude of the clouds above the stratosphere causes the sun to hit the crystals below, even if it is beyond the horizon, which is when these clouds appear brightest.
[Photo: Jónína Guðrún Óskarsdóttir]
Rainbow Clouds over the Arctic
A few days ago, the Arctic Circle was the scene of extraordinary rainbow clouds. This was not an isolated phenomenon, but gigantic clouds that covered the entire Arctic from Iceland, through Norway and even reached Finland.
Photographer Jónína Guðrún Óskarsdóttir captured the vibrant clouds over the peak of Iceland’s Mount Jökultindur. But she wasn’t the only one to spot the phenomenon at just the right moment, Frederik Broms fired the shutter on his camera to capture a series of snapshots depicting the colorful lights over Kvaløya near Tromsø in Norway.
[Photo: Jónína Guðrún Óskarsdóttir]
There are two types of rainbow clouds. Type I clouds are formed by a mixture of ice crystals and nitric acid that produce less iridescent colors and are known to be related to holes in the ozone layer. Type II rainbow clouds, on the other hand, are formed by pure ice crystals and have the property of refracting light in a more pristine way, which is why they generate much more colorful and iridescent colors with pearly textures and have even been confused with aurora borealis, but it should be clarified that these are two completely different phenomena.
Type II rainbow clouds are much rarer than type I clouds and occur only two or three times a year over the Arctic, during the winter months when temperatures in the stratosphere drop below -80ºC. However, experts believe that as climate change progresses, rainbow cloud types may appear more frequently in northern skies as a consequence of global temperature transformations.
Story originally published in Spanish in Ecoosfera