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Chapter 20
The mean values of the global PAR relative irradiance in umbra
(Fig. 10) decrease with the path length, although the dispersion is relatively
constant
The mean values of the PAR relative irradiances in sun flecks
slowly decrease from 1 at the upper forest level (L=0) to 0.92 at
with
A decrease of the diffuse component of the global irradiance is
responsible for this diminution.
In penumbra, the IPDF has a U-shape determined by the parameters
and
The vertical profile of the parameter is exhibited in Fig. 11. The
parameter is almost independent of and equals 0.6. In the upper layers of
the forest, the right part of the U-shape (high irradiances) is dominating
while the left part is regenerated. The situation is reversed in the lower layers
of the canopy.