This is the first day I have seen were there were no obvious clouds. This reveals the cold sky pyrgeometer values.
However there is a surprise, the pyranometer short wave solar hump is considerable offset in time from the shallow hump of long wave. Eyeballing it looks 2 to 3 hours later.
Lidar might give a clue. This shows low altitude return which looks coherent with long wave. A detail if you look closely, very low level higher reflection during the morning, perhaps excess night humidity burning off.
Air temperature peaks later too from a morning below zero. (from memory it was too dry for a frost, cold previous day)
This perhaps gives a clue too. There is reduced water vapour 10 to 13hrs a few km up. Could this be solar heating from the top?
Rather than deluging with all the plots, files are provided.
Commentary on what is going on is welcome.
I am putting the day files in an archive, 19th Feb 2013 here chilbolton-2013-02-19.
I thank Chilboton Observatory for their data.
Post by Tim Channon