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We had a bulletin from the BAA yesterday evening about the formation of Nacreous Clouds (or Polar stratospheric clouds) over the UK on Monday evening.
To quote from the BAA:
Nacreous clouds were seen from Cambridge this evening. This type of cloud is fundamental to the creation of the ozone hole over Antarctica and is rarely seen from the UK. The clouds form over the polar regions at heights of around 10 to 20km. They are usually visible during civil twilight - the denser cloud has beautiful pearly coloured margins and is quite bright, but there is also a diffuse component that appears like stratocumulus cloud, but is much higher.
This winter has seen an unusually cold Arctic stratosphere, and over the last couple of days the "polar vortex" with the coldest air has become very elongated and has reached down to the UK. There is a small chance that the
clouds might again be visible before sunrise on February 2, but after that the area of cold air moves away from the UK.
However, a further update this morning tells us that the latest forecasts now suggest that the conditions that lead to their formation will persist over the UK for several days, perhaps until the evening of February 4.
Given that it is likely to be clear this evening, this is definitely something to look out for. As Jonathan Shanklin from the BAA states, it could be many years before we see them again.
Posted : 02/02/2016 9:10 am
Topic starter
The BBC have put a page up containing images from yesterday evening:
Posted : 02/02/2016 9:12 am
Topic starter
Sunset this evening is 16:50, with civil twilight (dusk) ending at 17:26.
Posted : 02/02/2016 9:15 am
Apparently they're colloquially known as 'mother of pearl' clouds - and you can see why. Quite beautiful.
Edit: It also sounds a lot nicer than 'nacreous'!
Posted : 02/02/2016 9:58 am
Topic starter
It also sounds a lot nicer than ‘nacreous’
Not a very pleasant word, is it?
So, I looked up the origin of the word, and it was first used in the 1830's, and it comes from the medieval latin / old Italian / Arabic name for "mother-of-pearl"... nacre / naccaro / naqqārah.
Obviously, that's why they are also called "mother of pearl" clouds!
Posted : 02/02/2016 11:33 am
The Galloway Astronomy Centre (basically, a B&B with telescopes - and dark skies!) has just posted on their Facebook page a couple of photographs of nacreous clouds, taken this morning.
Posted : 02/02/2016 4:59 pm
Topic starter
Tried to see if I could see any from Greenwich Park last night, but no luck.
Still, it was a stunning sunset:
Sunset from West-side of Greenwich Park by Mike Meynell, on Flickr
Posted : 03/02/2016 7:43 am
Is that an eensie-weensie spider in the top right? 😉
Posted : 03/02/2016 9:34 am
Topic starter
Is that an eensie-weensie spider in the top right?
🙂 Should have cropped that out, shouldn't I!
No, it's a twig from an overhanging tree.
Posted : 03/02/2016 10:01 am
No, it’s a twig from an overhanging tree.
That's a relief. Because it was either a very large spider or it was very close. Neither situation is a good.
Twitter users can see a bunch more nacreous cloud photos here. Note the #motherofpearl hashtag.
Posted : 03/02/2016 10:35 am
Wow, nice sunset photo and perfectly positioned spider to boot! 😀
Thanks for the news, but question...why are these clouds only seen before dusk or after sunrise? Why not any time of the day? What is giving these particular clouds colour, is it the sun's reflection at certain angles, hence the specific times to see them?
Posted : 03/02/2016 12:14 pm
why are these clouds only seen before dusk or after sunrise?
I'm pretty sure it's because the sun reflects off the underside of the clouds. During the day it will shine right through - and at night, well, you can finish that sentence yourself 😉
Posted : 03/02/2016 12:33 pm
Topic starter
why are these clouds only seen before dusk or after sunrise
You need reflected sunlight for them to be visible. As the clouds are so high (12-15 miles+), the clouds remain lit by sunlight, even when the sun has set. They can be visible for up to 2 hours before sunrise or after sunset, apparently, because of their great height in the sky.
What is giving these particular clouds colour, is it the sun’s reflection at certain angles, hence the specific times to see them
Yes, it's caused by sunlight diffracting as it passes around the tiny ice crystals within the cloud.
Unfortunately, nacreous clouds are quite bad news for the environment, even though they are beautiful. The ice crystals also encourage chemical reactions between the ozone and the chemicals that we have introduced into the atmosphere by our use of CFCs. This causes ozone breakdown to take place.
CFCs have been phased out, but they will be in our atmosphere for many decades yet.
Posted : 03/02/2016 12:34 pm
<div class="d4p-bbt-quote-title">Tej wrote:</div>
why are these clouds only seen before dusk or after sunriseYou need reflected sunlight for them to be visible. As the clouds are so high (12-15 miles+), the clouds remain lit by sunlight, even when the sun has set. They can be visible for up to 2 hours before sunrise or after sunset, apparently, because of their great height in the sky.
<div class="d4p-bbt-quote-title">Tej wrote:</div>
What is giving these particular clouds colour, is it the sun’s reflection at certain angles, hence the specific times to see themYes, it’s caused by sunlight diffracting as it passes around the tiny ice crystals within the cloud. Unfortunately, nacreous clouds are quite bad news for the environment, even though they are beautiful. The ice crystals also encourage chemical reactions between the ozone and the chemicals that we have introduced into the atmosphere by our use of CFCs. This causes ozone breakdown to take place. CFCs have been phased out, but they will be in our atmosphere for many decades yet.
Oh no, thats a frightening reply! Go away CFCs and take your nacreous clouds with you!
Posted : 03/02/2016 1:14 pm
<div class="d4p-bbt-quote-title">Tej wrote:</div>
why are these clouds only seen before dusk or after sunrise?I’m pretty sure it’s because the sun reflects off the underside of the clouds. During the day it will shine right through – and at night, well, you can finish that sentence yourself
Ah simple logic, thanks Andy. So at other times, it reflects outwardly into space which Tim Peake should get a an even longer (and horrifying) view of!
Posted : 03/02/2016 1:21 pm
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