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1.0
50
0.8
25
0.6
0
0.4
-25
0.2
-50
0.0
1.0
50
0.8
25
0.6
0
0.4
-25
0.2
-50
0.0
1.0
50
0.8
25
0.6
0
0.4
-25
0.2
-50
0.0
0
50
100
150
200
x z
m
Figure 3.11
Sketch of the footprint for lux observations at location (
x, y, z
) =
(0, 0,
z
m
) for unstable (top), neutral (middle) and stable (bottom) condition (
z
m
/L
equal to -1, 0 and +0.5; for deinition of
L
see
Section 3.5.1
). Shades indicate the
fraction of the observed lux recovered from the indicated surface. White and black
isolines indicate the area from which 50% and 90% of the lux originate, respectively.
Figures are based on the model of Kormann and Meixner (
2001
). Note that horizon-
tal distances are scaled with the observation height
z
m
.
z
s
surface
Figure 3.12
A change of the lux with height (lux divergence) leads to change in the
storage in the control volume.
3.4.3 The Atmospheric Surface-Layer and the Roughness Sublayer
The turbulent luxes derived in
Section 3.4.1
are deined at an arbitrary height. But if
we are interested in exchange processes at Earth's surface, we need to have informa-
tion about the
surface
luxes. To determine the link between the surface lux and the
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