MODELING THE WATER BALANCE COMPONENTS OF THE SOYBEAN CANOPY BY SOIL-VEGETATIONATMOSPHERE TRANSFER MODEL - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 49

0.25

H =1.5 m

0.20

H =2.0 m
=2.5 m H

0.15

0.10

0.05

0.00

0.2 0.4 0.6 0.8 1.0

-

C d L d ( H-h )

Figure 3. Calculated value s o f the scaling length, σ , as a function of the leaf drag coefficient ( C d ), area-
averaged canopy density ( L ) canopy height ( H ), and canopy bottom height ( h ), for three tall grass

d

canopy heights.

0.14

0.12

0.10

0.08

0.06

0.04

1.00 1.25 1.50 1.75 2.00 2.25 2.50

Canopy height, H (m)

Figure 4. Calculated values of the canopy bottom height ( h ) as a function of the canopy height ( H ) for
tall grass vegetation. The fitting curve is drawn using data from Dubov et al. (1978), Sellers et al.
(1986), Mihailovic and Kallos (1997), Mihailovic et al. (2000) and Mihailovic et al. (2006)
[30,31,19,35,36].

Between the canopy height and canopy bottom height, the wind profile attenuates
exponentially according to Eq. (19), while beneath the canopy bottom height it follows a
classical logarithmic profile of the form

⎡ 1 h ⎤

⎛ ⎞

u ( H ) exp − β ⎝ 1 − ⎠

⎣ ⎦

2 H z

u ( z ) = ln . (26)

h

z

ln

g

z

g

Finally, since we know u ( z ), the variation of wind speed with height inside the canopy,
we can derive an expression for the canopy source height, h a . Assuming that the canopy
density is constant with height and combining Eqs. (15) and (16), we reach equality: