The Polar Region is full of nature’s incredible wonders. The perks of living in the sparsely populated land beyond the Arctic Circle Line is more than any nature enthusiast could ask for! Having seen a few of these wonders with my own eyes, I can confirm that!
In the list of the most sought after nature splendours in the Arctic Land are Aurora Borealis (Northern Lights), Polar Nights, Midnight Sun, Sun & Moon Halos, Coronas and Anticoronas around the Sun, Water Sky and Ice Blink, Mirages and optical illusions like fata morgana, Optical Haze, Sun Dogs, and Whiteout.
The current Aurora Season (2021-22) has exceeded all the shows in recent years and turned out to be the most glorious in decades. Almost every night, the Arctic sky has stayed alit with magical Aurora dance in the Nordic region above Arctic Circle. Other nature wonders keep stunning locals and tourists from time to time. Recently, the sunset sky in Lapland was adorned with Polar Stratospheric Clouds (PSC).
What are Polar Stratospheric Clouds & how do they form?
Casting an iridescent pastel hue in the Arctic sky immediately after sunset, the rare and one of the most beautiful polar stratospheric clouds is nature’s another wonder from the Polar region.
Also known as Nacreous clouds or Ice Polar Stratospheric Clouds, or Mother-of-Pearl Clouds, these clouds are rare and unique, having aroused the curiosity of nature admirers, scientists, and environmentalists alike, for different reasons.
Polar stratospheric clouds (PSCs) form during winter months in the Polar Stratosphere region at altitudes ranging from 15000-25000 meters. PSC appear as beads or patches of pearl fused into the bright sky mostly before sunset. Sources also mention that PSC can be best observed during Civil Twilight when the Sun is between 1-6 degrees below the horizon, mostly at northern latitudes.
PSC primarily comprises supercooled water droplets and Nitric Acid, which implies its role in Ozone Hole formation. Another PSC type comprises only ice crystals, which doesn’t harm the environment. The other major PSC type consists only of ice crystals which are not harmful. This sort of PSC is also referred to as nacreous (from nacre, or mother of pearl, due to its luminescence).
PSC resemble Cirrus or Altocumulus lenticularis showing significant irisation. It appears similar to the mother of pearl. The most radiant colours of PSC are observed when the Sun is a few degrees below the horizon.
Where can you find Polar Stratospheric Clouds?
Ice polar stratospheric clouds (PSC), or nacreous clouds, appear especially at high latitudes during the winter months. For PSC to form, the temperatures in the stratosphere must fall below the frost point. This phenomenon is the most common in Antarctica but has also been spotted in the Arctic, Scotland, Scandinavia, Alaska, Canada and the northern Russian Federation.
Are Polar Stratospheric Clouds harmful to the atmosphere?
The presence of PSC encourages a chemical reaction that breaks down the ozone layer. The ozone layer basically shields us from the sun’s harmful rays. Nacreous clouds are not entirely water droplets but a blend of naturally occurring water and nitric acid from industrial sources.
Substances like chlorofluorocarbons (CFCs) in aerosols and refrigeration have an adverse impact on the environment because these chemicals stay in the atmosphere for a prolonged time. CFCs take several years to rise through the troposphere until they make it to the Stratosphere, where they begin to break down by ultraviolet light producing free chlorine atoms. Chloride ions are highly reactive and continuously attack and destroy the ozone layer.
During the long winter months in the polar regions where there is little sunlight, temperature becomes so frigid in the Stratosphere that clouds start forming despite the air being so thin and dry.
These nacreous clouds formed out of frozen water crystals, nitric acid and sometimes sulphuric acid provide an ideal surface upon which chemical reactions occur that release the free chlorine atoms back into the atmosphere. The presence of sunlight is essential to the equation, so this happens only during spring when sunlight returns to the poles, and ultraviolet light break the bonds between the chlorine atoms. The process ends only when air flows from lower latitudes destroy the PSC or nacreous clouds.
Such chemical reactions could not take place anywhere else in the atmosphere. That is why the ozone hole is more prominent in the polar regions than elsewhere. The fact that nacreous clouds are commonly observed in the southern hemisphere entails that the ozone layer is more depleted over the south pole when compared with the north pole.
PSC formation has other adverse impacts as it also removes the gaseous nitric acid from the stratosphere. The Nitric Acid would otherwise combine with ClO, thus forming less reactive chlorine forms.
Referred source: National Snow & Ice Data Center
What are the other natural wonders not discussed in this blog that fascinates you? Do share your thoughts in the comments below. If you liked reading this piece, share it with your connections and subscribe to my blog.
For more such content, let’s connect on Instagram & Facebook