The Turbulent Lagrangian Time Scale in Forest Canopies Constrained by Fluxes, Concentrations and Source Distributions
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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.
KeywordsAtmospheric dispersion Lagrangian time scale Micrometeorology Turbulent transport Plant canopies
We gratefully acknowledge the expert technical assistance of Steve Zegelin, Dale Hughes, Mark Kitchen, Richard Hurley, Martin Riggenbach and Graham Kettlewell. Thanks also to David Jupp for supplying the ground-based lidar data and Heather Keith and Stephen Livesley for the ground CO2 flux measurements. Mike Raupach and Ian Harman kindly reviewed the manuscript and provided helpful suggestions.
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- Denmead OT, Raupach MR, Leuning R, Dunin FX, Freney JR (2005) Inverse Lagrangian analysis of heat, vapor, and gas exchange in plant canopies. In: Sadler EJ, Ham JM, Tanner B, Baker JM, Hatfield JL (eds) Micrometeorolgical measurements in agricultural systems. American Society of Agronomy, MadisonGoogle Scholar
- Doherty J (1999) PEST. Watermark numerical computing, Townsville, AustraliaGoogle Scholar
- Fest BJ, Livesley SJ, Drosler M, van Gorsel E, Arndt SK (2008) Soil–atmosphere greenhouse gas exchange in a cool, temperate Eucalyptus delegatensis forest in south-eastern Australia. Agric Forest Meteorol. doi: 10.1016/j.agrformet.2008.09.007
- Goudriaan J, van Laar HH (1994) Modelling potential crop growth processes, Current Issues in Production Ecology, vol 2. Kluwer, Dordrecht, p 238Google Scholar
- Griffith DWT (2002) FTIR measurements of atmospheric trace gases and their fluxes. In: Chalmers JM, Griffiths PR (eds) Handbook of vibrational spectroscopy. Wiley, Chichester, pp 2823–2841Google Scholar
- Kaimal JC, Finnigan JJ (1993) Atmospheric boundary layer flows: their structure and measurement. Oxford University Press, New York, p 289Google Scholar
- Raupach MR (2001) Inferring biogeochemical sources and sinks from atmospheric concentrations: general considerations and applications in vegetation canopies. In: Schulze ED (eds) Global biogeochemical cycles in the climate system. Academic Press, San Diego, p 350Google Scholar
- Styles JM, Raupach MR, Farquhar GD, Kolle O, Lawton KA, Brand WA, Werner RA, Jordan A, Schulze ED, Shibistova O, Lloyd J (2002) Soil and canopy CO2, (CO2)-C-13, H2O and sensible heat flux partitions in a forest canopy inferred from concentration measurements. Tellus B Chem Phys Meterol 54: 655–676. doi: 10.1034/j.1600-0889.2002.01356.x CrossRefGoogle Scholar
- Wohlfahrt G (2004) Modelling fluxes and concentrations of CO2, H2O and sensible heat within and above a mountain meadow canopy: a comparison of three Lagrangian models and three parameterisation options for the Lagrangian time scale. Boundary-Layer Meteorol 113: 43–80. doi: 10.1023/B:BOUN.0000037326.40490.1f CrossRefGoogle Scholar