"Graham P Davis" wrote in message
-jade...
On Mon, 1 Feb 2016 13:08:04 -0800 (PST)
Stephen Davenport wrote:
On Monday, February 1, 2016 at 1:11:06 PM UTC-5, Trevor Harley wrote:
Behind the view of flying trees and roofs there was quite a good
display of iridescent (I think they are) clouds this evening.
http://trevorharley.com/trevorharley/Weather.html
Trevor
The Sidlaws, NW of Dundee
========
These are polar stratospheric clouds (PSCs), a.k.a. nacreous clouds.
My news and social feeds are full of pictures of them remarkably far
south (Buckinghamshire, for example). Or perhaps not so remarkably
when you look at how very cold (and moist) the stratosphere is over
the UK due to circumpolar vortex displacement (in turn due to ongoing
stratospheric warming Pacific-side). Temperatures are between -80 and
-85C at 50hPa, for example, and below -85C at 30hPa (and PSCs form
below -78C):
http://users.met.fu-berlin.de/~Aktue...ecmwf50a12.gif
http://users.met.fu-berlin.de/~Aktue...ecmwf30a12.gif
A while ago, I came across a report of iridescent clouds in Central or
tropical South America that someone thought might be nacreous clouds. I
checked the local ascents and found the temperatures were just about
low enough in the stratosphere for that to be possible. I don't think
they were nacreous clouds but I think it's just possible that they may
be seen anywhere.
--
Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer]
http://www.scarlet-jade.com/
I wear the cheese. It does not wear me.
Posted with Claws: http://www.claws-mail.org/
That is a difficult observation Graham, one I would question.
I spent some years in the tropical Pacific in Vanuatu (17S 168E) flying
sondes. The temperature at the tropopause sometimes got as low as -85C, but
always rose quite rapidly as you went into the stratosphere, reaching
ca. -30C near 10 mbar. Our ascents reached between 34 and 36 km regularly,
where the temperature could be as high as -15C, but I can't recall ever
seeing a secondary temperature minimum above the tropopause.The trop. was
always higher (above the ground) than 150 mbar, and could be as high as 90
mbar on occasions. I observed (on radar) a Cb top reaching 18 km, 2 km above
the trop on that day, and would have had an in-cloud temperature well
below -90C. Iridescence was not infrequent near sunrise/sunset, but was
always (in my experience) tropospheric cloud, albeit high. The -40C isotherm
was often near 10km, so thin Ac cloud could occur up to 30000 ft plus at
least. High, sometimes thin, cirrus could sometimes be seen near the trop.
at dawn/dusk, but was mostly Cb debris, although the sub-tropical jet could
sometimes buckle enough to allow jet-stream Ci/Cs to appear at 17S., but
this was usually much thicker and chunkier looking, and both didn't produce
iridescence.
--
Bernard Burton
Wokingham Berkshire.
Weather data and satellite images at:
http://www.woksat.info/wwp.html