Stratospheric Cloud Alert

Last updated on September 16, 2023

Stratospheric Cloud Alert: A Spectacular Atmospheric Phenomenon

Have you ever witnessed a breathtaking sunset or a prolonged twilight that left you in awe? On the evening of Tuesday, January 26th, residents of southern and eastern England, as well as The Netherlands, were treated to a mesmerizing display of vibrant colors in the sky. These stunning visuals were not limited to just these regions, as they were likely visible over an even wider area. The sight was so captivating that it caught the attention of atmospheric optics experts and photographers, who captured the beauty through their lenses.

One such expert, Peter Paul Hattinga Verschure, observed a sunset in Deventer, The Netherlands, where the sun glowed in brilliant shades of orange and red. He noted that these hues were visible through a thin layer of high clouds, creating a truly magical atmosphere. Another photographer, Pete Glastonbury, captured the twilight scene in Devizes, Wiltshire, England, where vivid reds painted the sky. These captivating images serve as a testament to the enchanting nature of our atmosphere.

A photograph taken by Rob Brocklehurst in Dorset, England, also showcases the post-sunset red and crimson hues. This captivating image further adds to the allure of the phenomenon. Approximately 25 minutes after sunset, Peter Paul Hattinga Verschure captured another scene in The Netherlands. He noticed that a sun-lightened cloud bank remained near the westerly horizon, while all other clouds and contrails darkened. This observation led him to speculate that these far clouds belonged to a higher atmospheric region known as the Polar Stratospheric Clouds (PSCs).

Polar Stratospheric Clouds (PSCs) are unique cloud formations that occur at heights ranging from 15 to 25 kilometers (9 to 16 miles) above our ordinary tropospheric clouds. These clouds require extremely low temperatures, reaching as low as minus 78 degrees Celsius, to form in the arid and low-density conditions of the lower stratosphere. There are two main types of PSCs: Type I and Type II.

• Type I PSCs are composed of nitrogen acid and water compounds.
• Type II PSCs, also known as nacreous clouds, are made of ice and emit a bright shine.

To form Type II PSCs, temperatures slightly lower than those required for Type I PSCs are necessary. The presence of these unique cloud formations adds a touch of mystery and beauty to our skies.

It is important to note that similar spectacular sunsets and twilights were observed in a large part of Europe in February 2008. These phenomena were caused by very low stratospheric temperatures and the presence of Type I PSCs. However, it is crucial not to rule out other possibilities, such as volcanic aerosol and dust, which can also contribute to similar atmospheric displays.

As we marvel at the start of this series of extraordinary sunsets, it is worth keeping an eye out for twilights and sunrise/sunset moments in the coming days. Nature never ceases to amaze us with its breathtaking displays, and the phenomenon of stratospheric clouds is yet another reminder of the wonders that surround us. So, let us embrace the beauty of our atmosphere and cherish these moments of awe-inspiring splendor.

Polar Stratospheric Cloud Alert

On the evening of Tuesday 26th January, southern and eastern England plus The Netherlands experienced spectacular colourful sunsets and prolonged twilights. Very likely they were visible over an even wider area.

The top left image shows a similar sunset witnessed at Deventer in The Netherlands by atmospheric optics expert Peter Paul Hattinga Verschure. He comments �The sun glowed up in bright orange and red colours, shining through a thin layer of high cloud�.�

At top right is the twilight scene of vivid reds imaged by Pete Glastonbury at Devizes in Wiltshire, England.

The third image is by Rob Brocklehurst taken in Dorset, England and also shows some of the post-sunset red and crimson hues.

Another Netherlands image by Peter Paul Hattinga Verschure is below and shows the scene 25 minutes after sunset.

Peter Paul comments �About half an hour after sunset, a sun-lightened cloud bank remained near the westerly horizon, while all other clouds and contrails were darkened. Obviously the far clouds were in a higher atmospheric region. So I guess that was a bank of Polar Stratospheric Clouds. The more because temperatures at 22 kilometres altitude were below -80 degrees Celsius. This should be then PSC of type I. The real nacreous clouds of Type II are never seen from our flat country.�

Polar Stratospheric Clouds, PSCs, occur at heights of 15-25 km (9-16 mile) and far above our ordinary tropospheric clouds. To form in the arid and low density conditions of the lower stratosphere they need temperatures of minus 78�C or colder depending on their composition. Type I PSCs are nitrogen acid and water compounds. Type 2, the brightly shining nacreous clouds, are ice and they need slightly lower temperatures.

A large part of Europe had similar spectacular sunsets and twilights in February 2008 caused by very low stratospheric temperatures and Type I PSCs (see the thumbnail links below).

Volcanic aerosol and dust give similar sunsets and we should not rule out these possibilities at this stage.

We could be seeing the start of a series of spectacular sunsets. Look out for twilights and sunrise/sets over the next few days.

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Reference Atmospheric Optics

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