"Graham Easterling" wrote in message
...
On Monday, June 9, 2014 12:50:49 PM UTC+1, Ian Bingham wrote:
Just bought a new (Met 01) Stevenson Screen. The interior is black
instead
of white as before. Does anyone know the scientific principle behind
this -
why should a black interior be superior to the usual white? It seems a
bit
of a contradiction as the black surface is shiny.

Ian Bingham

Inchmarlo, Aberdeenshire.

You may be interested in these comments by Steven Burt on COL forum

"The rationale behind the black interior is indeed a bit of a puzzle, one
Ian Strangeways and myself have spent several years trying to get to the
bottom of, with rather ambiguous results. Tests run by the Met Office in
2000/01 showed that black-interior screens had slightly lower maxima than
white interior versions in strong sunshine, and thus were presumably more
effective at blocking solar radiation. Other tests have been run by other
authorities, most recently one by Campbell Scientific in the UK, and the
black screens do seem to offer slightly better performance than the white
interior versions. (If you'd like to see copies of the reports, please drop
me an e-mail and I'll send them to you; I've also covered the topic in my
forthcoming book on weather observing, which will be published in July -
http://www.cambridge.org/9781107662285 )

While accepting that the tests were rigorous and the reported differences
are genuine, I'm not 100% convinced that the difference is due simply to the
black plastic material used having different (more opaque) radiative
properties in the infra-red than the equivalent white plastic, rather than
their colour in the visible spectrum. A black-interior plastic screen is
also a poor choice for a site where the screen is opened several times a
day, as it would have been before most sites moved to remote-reading and/or
logged equipment, as the temperature does rise quickly in sunshine when the
door is opened, more so than a white interior model. I keep mine firmly shut
during the day!

I've compared the observed max and min temperatures in the two screens
carefully over the last 6 months, and find the differences small - the
Metspec screen appears to be slighly more responsive, probably because it is
smaller than the large wooden screen and thus has less thermal inertia.
However, the differences are within calibration tolerances, so I'm happy
that swapping the wooden one for the plastic one isn't going to disrupt the
continuity of my records."

Graham
Penzance (still with a trad white wood screen)
=======================

I've had a black interior MetSpec screen since 2004 and the best bit about
it is there is no need to paint it! Just a clean now and again and even that
is easier. They aren't cheap though, I paid £450 (without stand) in 2004 - a
lot of money to house max/min thermometers and even they cost £100 each!
The screen maxes tend to be close to my £700 Davis AWS (at same height) but
the mins are lower as the AWS is more exposed to small air currents.

Will
--
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
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