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)