On Feb 2, 11:04 pm, "Dave Liquorice" wrote:
On Fri, 2 Feb 2007 18:07:01 -0000, David Mitchell wrote:
Visible to the south east after 0800 today. Only a small patch but
the first I've seen for some time.

Are you sure it wasn't iridisation in some high cirrus?

Thanks for the reply guys and I can assure you it was a single small
cloud.

But surely at 0800 the sun is above the horizon. IIRC you only see
nacreous cloud when the sun is below the horizon.

There are a few reliable reports of nacreous clouds (particularly the
slightly denser lenticular ones that appear "bright white" with green-
red pastel interference fringes at the edge) being seen with the sun
*just* above the horizon. The highly coloured ones though are
virtually transparent and disappear very quickly at sunrise (I have
never seen them in the morning myself).

http://www.meteo.be/english/index.php?doc=OzonEN

The ozone level over Uccle in Belgium (real time graph) shows a slight
dip recently, but not a major collapse as would be expected if there
had been a significant region with PSCs forming in the stratosphere.

AFAIK there is only one fully daytime observation of nacreous? clouds
in 1951 August 10 1230-1330 (an unusual date too - most UK displays
are seen in winter). He was only able to see the cloud after climbing
to above 30000 feet. This particular observation was made by a test
pilot in experimental British jet aircraft who flew through a nacreous
cloud and reported it as being at extremely high altitude located
between 46500 and 47500 feet and optically thin. The air temperature
in the cloud was measured as -56C (which sounds about 20 degrees too
warm for PSCs to me) The pilot remarked that in his entire career he
had never before seen any clouds above 42000 feet whilst testing
aircraft up to 50000ft. I believe this one summer observation is
unique in the UK.

The pilot is not named, but the anonymous report is "Very high cloud
layer, August 10 1951", Meteorological Magazine, 80, p365-6.

Regards,
Martin Brown