Leaf area index and topographical effects on turburlent diffusion in a deciduous forest
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Date
2012
DOI
Open Access Location
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Publisher
Massey University
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Abstract
In order to investigate turbulent diffusion in a deciduous forest canopy, wind velocity
measurements were conducted from late autumn of 2009 to early spring of 2010, using an observation tower
20 m in height located in the campus of Kanazawa University. Four sonic anemometers mounted on the
tower recorded the average wind velocities and temperatures, as well as their fluctuations, at four different
heights simultaneously. Two different types of data sets were selected, in which the wind velocities, wind
bearings and atmospheric stabilities were all similar, but the Leaf Area Indexes (LAI's) were different.
Vertical profiles of average wind velocities were found to have an approximately exponential profile in each
case. The characteristic length scales of turbulence were evaluated by both von Karman's method and the
integral time scale deduced from the autocorrelation from time-series analyses. Both methods produced
comparable values of eddy diffusivity for the cases with some foliage during late autumn, but some
discrepancy in the upper canopy layer was observed when the trees did not have their leaves in early spring.
It was also found that the eddy diffusivities generally take greater values at higher positions, where the wind
speeds are large. Anisotropy of eddy diffusivities between the vertical and horizontal components was also
observed, particularly in the cases when the canopy does not have leaves, when the horizontal eddy
diffusivities are generally larger than the vertical ones. On the other hand, the anisotropy is less visible when
the trees have some foliage during autumn. The effects of topography on the turbulent diffusion were also
investigated, including evaluation of the non-zero time-averaged vertical wind velocities. The results show
that the effects are marginal for both cases, and can be neglected as far as diffusion in the canopy is
concerned.
Description
Keywords
Forest canopy, Deciduous forest canopy, Canopy flow, Wind turbulence, Eddy diffusion, Leaf area index, Micro-climate
Citation
Kimura, S., McKibbin, R., Ogawa, J., Kiwata, T., Komatsu, N, Nakamura, K. (2012), Leaf area index and topographical effects on turburlent diffusion in a deciduous forest, Research Letters in the Information and Mathematical Sciences, 16, 1-22