Nacreous Clouds (Mother of Pearl) - Have You Seen Them?

[martinastro]

I have been researching the remarkable phenomena of Nacreous Clouds, also known as 'Mother of Pearl' or 'Polar Stratospheric Clouds' (PSCs). They normally form during Winter months at high latitudes and are very rare over the UK. During the ninties there where wide spread spectacular displays over UK and Ireland reaching as far south as England. I have never seen them before but will be scanning for them after sunset, and before dawn, over the Winter Months ahead. My question is, has anyone on here ever seen them?, and have you any images?. Thanks in advance.

I've asked the same question on the UKWW.

Here's a nice youtube video clip

[martinastro]

Jonathan Bingham reports seeing them from NI in the nineties, and I think Dr. Andy Mc Crea observed and even photographed them too.

John Mason told me he seen a display on April 1989 from NW Scotland on a cold snow day, he's currently looking for the slides at the moment.

Anyone else?

[brianb]

Can't remember seeing them, ever. How long after sunset / before sunrise?

[paulster78]

Never seen anything like that before, what kind of atmospheric conditions are needed for these nacreous clouds to appear Martin?  I'll be keeping a lookout for them now too.

[martinastro]

Brian, I believe they are little like NLCs and are best 1 to 2 hours after sunset and again before dawn, although on occasion they are visible in daylight.

Paul, frigid temps in the stratosphere are needed for their formation, that's all I know.

[martinastro]

This is from Les Cowley

Nacreous clouds, sometimes called mother-of-pearl clouds, are rare but once seen are never forgotten. They are mostly visible within two hours after sunset or before dawn when they blaze unbelievably bright with vivid and slowly shifting iridescent colours. They are filmy sheets slowly curling and uncurling, stretching and contracting in the semi-dark sky. Compared with dark scudding low altitude clouds that might be present, nacreous clouds stand majestically in almost the same place - an indicator of their great height.

They need the very frigid regions of the lower stratosphere some 15 - 25 km (9 -16 mile) high and well above tropospheric clouds. They are so bright after sunset and before dawn because at those heights they are still sunlit. They are seen mostly during winter at high latitudes like Scandinavia, Iceland, Alaska and Northern Canada. Sometimes, however, they occur as far south as England. They can be less rare downwind of mountain ranges. Elsewhere their appearance is often associated with severe tropospheric winds and storms. Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds which are very much poor relations and seen frequently all over the world.

Nacreous clouds are wave clouds. They are often found downwind of mountain ranges which induce gravity waves in the lower stratosphere. Their sheet-like forms slowly undulate and stretch as the waves evolve. The clouds can also be associated with very high surface winds which may indicate the presence of, or induce, winds and waves in the stratosphere. They form at temperatures of around minus 85ºC, colder than average lower stratosphere temperatures, and are comprised of ice particles ~10µm across. The clouds must be composed of similar sized crystals to produce the characteristic bright iridescent colours by diffraction and interference. Nacreous clouds are a type of Polar

POLAR STRATOSPHERIC CLOUDS

Type II
Nacreous clouds composed of ice crystals with temperatures of ~minus 85ºC.   

Type I
Less spectacular than nacreous clouds, more diffuse and less bright colours. Sometimes nacreous clouds are embedded in them. Type I clouds are slightly warmer (~ minus 78ºC) than Type II and are composed of exotic solids or liquid droplets.

Type Ia
Crystalline compounds of water and nitric acid - especially NAT, nitric acid trihydrate HNO3.3H2O

Type Ib
Small spherical droplets of a solution of nitric and sulphuric acids.

Type Ic
Small non spherical particles of a metastable nitric acid - water phase

PSCs were long regarded as curiosities and of no real consequence. However, Type I clouds are now known as sites of harmful destruction of stratospheric ozone over the Antarctic and Arctic.  Their surfaces act as catalysts which convert more benign forms of man-made chlorine into active free radicals (for example ClO, chlorine monoxide). During the return of Spring sunlight these radicals destroy many ozone molecules in a series of chain reactions. Cloud formation is doubly harmful because it also removes gaseous nitric acid from the stratosphere which would otherwise combine with ClO to form less reactive forms of chlorine.

[Roman White]

I have seen some reports (not recent) from Murmansk (69N latitude)

[jjb]

Martin i recall it was the early nineties i wonder would the local met office have any records of it i must hunt out my old photos just incase i took some of them.

jonathan.

[martinastro]

Cheers Jonathan, if you could find any images that would be cool. Many reports from that period seem to be from 1996, I wonder if that was the same year.

[markt]

Hi Martin.
I don't think i've seen Nacreous clouds, but I regularly see alot of iridescence in clouds.  Living just to the east of the welsh mountains lee wave clouds are reasonably common, and these, coupled with iridescence can /could look quite similar to Nacreous to the untrained eye.  The 2 forming processes are completely different though.  Next time we get some i'll make sure I get a picture!
Mark

[JohnC]

What a wonderful sight .I'd love to see them.

[martinastro]

Thanks for the info Mark!

John, I too would love to see them, they could appear anytime from now on...

[Mickyjoe]

wow...beautiful clouds. i will keep an eye out for this, i just love clouds..im always out before sunset and sometimes i see weird but nice cloud formations and colours. this is very interesting. thanks for this martin...good job