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Wind Profiles in Plant Canopies: Studies on an Analytical Model

J. J. Landsberg and G. B. James
Journal of Applied Ecology
Vol. 8, No. 3 (Dec., 1971), pp. 729-741
DOI: 10.2307/2402680
Stable URL: http://www.jstor.org/stable/2402680
Page Count: 13
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Wind Profiles in Plant Canopies: Studies on an Analytical Model
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Abstract

Wind profiles measured in a spruce forest, and published profiles, measured in maize (Uchijima & Wright 1964), beans (Thom 1967) and an orange orchard (Kalma 1970) are analysed in terms of a model derived independently by Thom (1971) and the authors. The equation is $$u(z) = u_h\big[1 + \alpha\big(1 - \frac{z}{h}\big)\big]^{-2}$$~ where $u$ denotes wind speed, $z$ is height and $h$ is the height of the top of the plant stand. The parameter $\alpha$ is defined as $h ~\surd(C_dU_hL/6K)$, where $C_d$ is the drag coefficient, $L$ is the average foliage density and $K$ is the momentum exchange coefficient (eddy viscosity). The assumptions used to derive the model appear to be valid for crops, such as maize and beans, where the foliage distribution is reasonably uniform. In such plant stands $\alpha$ may be derived from a single in-crop wind speed measurement, and a measurement of $u_h$. Where foliage is not uniformly distributed the model profiles only fit well over part of the measured profiles. The model does not allow separation of the drag coefficient and eddy viscosity terms, but given adequate information on effective drag coefficients the parameter $K/C_d$ would yield an immediate estimate of $K$.

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