The Turbulent Lagrangian Time Scale in Forest Canopies Constrained by Fluxes,Concentrations and Source Distributions |
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| Authors: | Vanessa Haverd Ray Leuning David Griffith Eva van Gorsel Matthias Cuntz |
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| Institution: | 1.CSIRO Marine and Atmospheric Research,Canberra,Australia;2.Department of Chemistry,University of Wollongong,Wollongong,Australia;3.Research School of Biological Sciences,Canberra,Australia;4.Max-Planck-Institut für Biogeochemie,Jena,Germany |
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| Abstract: | One-dimensional Lagrangian dispersion models, frequently used to relate in-canopy source/sink distributions of energy, water
and trace gases to vertical concentration profiles, require estimates of the standard deviation of the vertical wind speed,
which can be measured, and the Lagrangian time scale, T
L
, which cannot. In this work we use non-linear parameter estimation to determine the vertical profile of the Lagrangian time
scale that simultaneously optimises agreement between modelled and measured vertical profiles of temperature, water vapour
and carbon dioxide concentrations within a 40-m tall temperate Eucalyptus forest in south-eastern Australia. Modelled temperature
and concentration profiles are generated using Lagrangian dispersion theory combined with source/sink distributions of sensible
heat, water vapour and CO2. These distributions are derived from a multilayer Soil-Vegetation-Atmospheric-Transfer model subject to multiple constraints:
(1) daytime eddy flux measurements of sensible heat, latent heat, and CO2 above the canopy, (2) in-canopy lidar measurements of leaf area density distribution, and (3) chamber measurements of CO2 ground fluxes. The resulting estimate of Lagrangian time scale within the canopy under near-neutral conditions is about 1.7
times higher than previous estimates and decreases towards zero at the ground. It represents an advance over previous estimates
of T
L
, which are largely unconstrained by measurements. |
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| Keywords: | Atmospheric dispersion Lagrangian time scale Micrometeorology Turbulent transport Plant canopies |
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