This Morning on the 28th of December we all woke up to a rare spectacle in the sky: Nacreous Clouds. It was very cold and windy outside but I quickly got dressed and jumped out with my camera to take pictures of this natural phenomenon.
Polar stratospheric clouds form in the lower stratosphere, often at an altitude of 15 – 30km (49,000–82,000 ft). As temperatures at this altitude are much lower, around -78 °C, ice crystals are smaller.
How Nacreous Clouds form
The ice crystals deflect the sunlight during sunrise or sunset when the sun is between 1° and 6° below the horizon. This happens in Iceland during the wintertime when the days are short and the sun is low above the horizon.
The result is the effect of cloud iridescence, the amazing rainbow effect that you can see in the pictures. Depending on the sunlight and your position, it can look different with more or less colorful shapes.
The clouds are also called “Mother of Pearl” and Glitský in Icelandic. The colors also depend on the distribution of particles in the clouds, so you can often see red, yellow, and green colors mixed.
Nacreous Clouds over Iceland
Although this phenomenon is rare, we are lucky enough to see Nacreous Clouds about once or twice a year. Often observed in the Countryside at sunset or sunrise, a description of this colorful spectacle was even found in an old book “Lýsing Íslands”- The quote of Þorvaldur Thoroddsen presumably dates back to the 17th century:
On the morning of the second day of Christmas, many large clouds were seen in the sky to the east and south and south of the country, incredibly beautiful, red and blue, green and yellow, one in the middle as beautiful as the moon, they were seen until daylight.
The weather was very calm with a light breeze from the south. The clouds were also seen on the third day. People observed them in the south and all over Iceland before Christmas and after.
“Lýsing Íslands” (second volume pp. 367-368) Þorvaldur Thoroddsen
This is possibly the oldest known description of Glitský (Glittering Clouds).
Also nice to witness: Northern Lights
The Dark Side of Nacreous Clouds
While Nacreous clouds enchant their viewers, they can have a destructive effect on our protective ozone layer. The ice crystals in the clouds boost a chemical reaction between gases such as bromine and chlorine which leads to the breakdown of ozone molecules. Without this protective layer in our atmosphere, harmful ultraviolet rays from the sun can reach the earth’s surface.
The main reason for these gases being in the atmosphere in the first place is us, humans. People used chlorofluorocarbons (CFCs) in products such as refrigerators and aerosol cans until 1987 when it was banned. However, it can take another 100 years before the effects of CFCs are reduced.
Sources
Explainer: what are the ‘nacreous clouds’ lighting up the winter skies?
Our beautiful planet: The dark side of ‘mother of pearl’ clouds