Geoscience Reference
In-Depth Information
Z
h
Modeled canopy
Figure 22.2
Specification of the
simple model canopy used to
investigate the variation of zero
plane displacement and
aerodynamic roughness with leaf
area index and the height
distribution of leaf area.
z
m
L
(
z
)
(a)
(b)
0.14
z
M
h
z
M
h
0.8
0.12
0.7
0.10
d
h
z
0
h
0.08
0.6
0.06
0.5
0.04
0.4
0.02
0.5
1
2
LAI
468
0.5
1
2
468
LAI
Figure 22.3
Modeled variations in (a) normalized zero plane displacement, (
d
/
h
), and (b) normalized aerodynamic
roughness, (
z
o
/
h
), as a function of the leaf area index, LAI, and the normalized position of peak leaf area in the canopy,
(
z
m
/
h
). (Redrawn from Shaw and Pereira, 1982, published with permission.)
where
h
is the height of the canopy and
LAI
is the total leaf area index of the
canopy. The variation of
d
and
z
o
was explored as a function of
LAI
and the ratio
(
z
M
/
h
), where
z
M
is the height with maximum leaf area, see Fig. 22.2.
The results of this modeling study are shown in Fig. 22.3. They show that the
normalized displacement height, (
d
/
h
), increases with (
z
M
/
h
), as might be expected,
and that (
d
/
h
) also increases with the total leaf area of the modeled canopy, again
as expected. For 'closed canopies, i.e., when
LAI
is typically in the range 2 to 6,
the modeled value of (
d
/
h
) is in the range 0.5 to 0.75, depending on the position
of maximum leaf area in the canopy. This is consistent with field observations.
The normalized aerodynamic roughness, (
z
o
/
h
), was modeled initially to increase
