We analyse observations of infrared crown radiation temperatures over a dense Douglas-fir forest stand obtained during one growing season. At day time these crown radiation temperatures can conveniently be described within the context of surface layer similarity and the surface roughness length for heat (see poster presentation). During night time frequently a decoupling of the crown radiation temperature from the air temperature aloft is observed. It is shown that a convective temperature comes into play which is coupled to the forest interior temperature.
Observed crown radiation temperature is then composed of this convective temperature and the aerodynamic surface temperature. Forest interior air temperature during night time is in general observed to be lower than air temperature above the canopy. A simple two layer canopy model is used to explain this behaviour in terms of the vertical distribution of atmospheric sensible heat flux and canopy storage heat flux over the crown layer.