Canopy wind profiles can often be represented by an exponential function. The associated attenuation index,a, is found to be proportional to [(Flexibility)(Leaf Area)(Density)]1/3. Leastsquare values of the index have been calculated for wind profiles in about a dozen natural and artificial canopies which included oats, wheat, corn, rice, sunflowers, larch trees, citrus trees, Xmas trees, plastic strips, wooden pegs and bushel baskets. It is found that canopy flow is a function of canopy density, element flexibility, and height and that the behaviour of artificial canopy elements is compatible with that of natural vegetation. The same calculations also show that the attenuation coefficient: (a) is not a universal constant, (b) is however, rather limited in range (∼-0.3 to 3.0), (c) varies with stage of growth, and (d) increases as density and flexibility increase. A compilation ofa-values for several canopies reveals that lowa-values correspond to sparsely arrayed rigid elements while higha-values correspond to densely arrayed and flexible elements. Finally, lowa-values appear to be relatively independent of wind speed, while higha-values tend to increase as wind speeds increase.
[1]
Y. Nakagawa.
Studies on the air flow amongst the stalks in a paddy field
,
1956
.
[2]
Erich J. Plate,et al.
Modeling of Velocity Distributions Inside and Above Tall Crops.
,
1965
.
[3]
Ronald M. Cionco,et al.
A Mathematical Model for Air Flow in a Vegetative Canopy
,
1965
.
[4]
Z. Uchijima.
Studies on the Micro-Climate within the Plant Communities
,
1962
.
[5]
Winton Covey,et al.
The energy-budget evaluation of the micrometeorological transfer processes within a cornfield
,
1966
.
[6]
Gaseous Exchange in Crop Stands
,
1969
.
[7]
L. H. Allen,et al.
Turbulence and Wind Speed Spectra within a Japanese Larch Plantation
,
1968
.
[8]
E. Inoue,et al.
On the Turbulent Structure of Airflow within
,
1963
.
[9]
O. Denmead.
Evaporation Sources and Apparent Diffusivities in a Forest Canopy
,
1964
.