Re: about the sky temperature

["Bengt Perers" <bpr@xxxxx>]

To mee the data seems reasonable at a quick glance.

I have experience from some years with infrared thermografy and image
processing + Poolheating. As rule of thumb for northern Europe at least the
effective sky temperature is about 10-20 degrees below the ambient
temperature at ground level at clear sky condtions and close to and just
below (1-2 deg) the ambient temperature during cloudy conditions. This is
independent on season. The low sky temperature is cause by radiation in the
artmospheric window at 8-14 um and is where all the discussion on
greeenhouse gasses have their main real effect.

There is a very nice text book on these radiation subjects for the
atmospehere and earth surface in the Infrared Handbook by W.L.Wolfe and G.J.
Zissis ISBN 0.9603590-1-X.

The shift at sunrise may correspond to that the realtive humidity and fog
content is decreasing rapidly at synrise when the moisture in the air is
heated by the sun again. We often not a dip in ambient temperture just after
the sunrise which you should not expect otherwise.

I am still an observer more than an expert but please tell me if you find
out something more.