The turbulent Lagrangian time scale in forest canopies constrained by fluxes, concentrations and source distributions
Vanessa Haverd1, Ray Leuning1, Eva van Gorsel1, David Griffith2, Matthias Cuntz3
1 Marine and Atmospheric Research, CSIRO
2 University of Wollongong
3 Helmholtz-Zentrum fur Umweltforschung
2 University of Wollongong
3 Helmholtz-Zentrum fur Umweltforschung
O 2.6 in Turbulence structure in and above forests
06.10.2009, 12:05-12:30, Kutschenhaus
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 windspeed, which can be measured, and the Lagrangian time scale, TL, 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, HDO and carbon dioxide concentrations within a 40-m tall temperate Eucalyptus forest in south-eastern Australia. Modelled temperature and concentration profiles are generated using a Lagrangian dispersion theory combined with source/sink distributions of sensible heat, H2O, HDO and CO2. These distributions are derived from a multilayer Soil Vegetation Atmospheric Transfer model subject to multiple constraints: (1) day-time eddy flux measurements of sensible heat, latent heat, and CO2 above the canopy, (2) in-canopy laser measurements of leaf area density distribution, (3) chamber measurements of CO2 ground fluxes and (4) deuterium isotopic content of soil and plant water and evaporative 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 TL , which are largely unconstrained by measurements.
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