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REVIEWS & ANALYSES

Modeling Heat, Water Vapor, and Carbon Dioxide Flux Distribution Inside Canopies Using Turbulent Transport Theories

^a Nicholas School of the Environment and Earth Sciences and Department of Civil and Environmental Engineering, Box 90328, Duke University, Durham, NC 27708-0328
^b Department of Civil and Environmental Engineering, Duke University, Durham, NC 27708
* Corresponding author (Gaby{at}duke.edu)

Received 28 November 2001.

This study reports recent developments in mulitlayer turbulent transport methods to compute distributions of strengths of scalar sources and sinks S_c as well as turbulent fluxes F_c within the plant–atmosphere continuum. In particular, we focus on the so-called "inverse methods" that estimate S_c from measured mean scalar concentration (or temperature) distribution within the canopy without resorting to any ecophysiologically based input. These approaches are able to reproduce measured turbulent fluxes above and within the canopy without relying on gradient diffusion formulation. Comparison between measured and modeled sensible heat flux vertical attenuation within the canopy suggests that all three methods provided comparable root-mean squared error (RMSE) (50 W m^-2). Furthermore, correcting for local atmospheric stability significantly improved the agreement between model calculations and measurements. Comparisons between measured and modeled land surface fluxes of sensible heat, latent heat, and CO₂ above the canopy are conducted using wavelet spectral methods applied to a wide range of temporal scales (30 min–2 yr). This study is the first to rigorously assess the performance of several inverse methods for such a broad range of time scales. We found that the three inverse modeled flux spectra bound the measured one. Hence, spectral agreement among the three models provides the necessary confidence in calculated fluxes and scalar sources. Conversely, large disagreement between the inverse models "flags" large uncertainties at those particular time scales.

Abbreviations: ASL, atmospheric surface layer • EUL, Eulerian closure "inverse" model • HEL, hybrid Eulerian–Lagrangian model • LNF, localized near field theory • ODE, ordinary differential equation