"Paul Hyett" wrote in message
...
What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

*I'm referring to nights with no frontal activity, of course.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Clouds absorb and re-radiate downwards the upwelling long-wave radiation
from the surface. When cloud cover replaces clear sky the surface radiation
continues, but can no longer escape to space. The air temperature near the
surface rises towards the ground temperature until a new balance is
achieved.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.woksat.info/wwp.html
or
www.btinternet.com/~wokingham.weather/wwp.html