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First- and Second-Order Closure Models for Wind in a Plant Canopy

J. D. Jean-Paul PinardDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada

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John D. WilsonDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada

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Abstract

Katul and Chang recently compared the performance of two second-order closure models with observations of wind and turbulence in the Duke Forest canopy, noting that such models “alleviate some of the theoretical objections to first-order closure.” This paper demonstrates that, notwithstanding those (valid) theoretical objections, Duke Forest wind simulations of comparable quality can be obtained using a first-order closure, namely, eddy viscosity Kλk, where k is the turbulent kinetic energy and λ is a turbulence length scale. It is concluded that, most often, uncertainty in the drag coefficient will limit the accuracy of modeled wind statistics, regardless of the turbulence closure chosen.

Corresponding author address: J. D. Jean-Paul Pinard, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada. jpinard@ualberta.ca

Abstract

Katul and Chang recently compared the performance of two second-order closure models with observations of wind and turbulence in the Duke Forest canopy, noting that such models “alleviate some of the theoretical objections to first-order closure.” This paper demonstrates that, notwithstanding those (valid) theoretical objections, Duke Forest wind simulations of comparable quality can be obtained using a first-order closure, namely, eddy viscosity Kλk, where k is the turbulent kinetic energy and λ is a turbulence length scale. It is concluded that, most often, uncertainty in the drag coefficient will limit the accuracy of modeled wind statistics, regardless of the turbulence closure chosen.

Corresponding author address: J. D. Jean-Paul Pinard, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada. jpinard@ualberta.ca

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