Quantifying net ecosystem exchange by multilevel ecophysiological and turbulent transport models

Abstract

To quantify the interplay between scalar sources and sinks (S c ) and net ecosystem exchange (NEE), ''forward'' and ''inverse'' approaches have been proposed. The canonical form of forward approaches is a one-dimensional ecophysiological-radiative transfer scheme coupled to turbulent transport theory. In contrast, inverse approaches strictly rely on turbulent transport theory and mean scalar concentration as their primary input to infer S c and NEE. While the formulation of both approaches have evolved over the past decade, no systematic comparison between them was undertaken for the same data set, and over a wide range of atmospheric conditions. Our objective is to compare the predicted S c and NEE from these two approaches with eddy-covariance measurements. The results show that the forward method outperformed all three inverse methods for unstable and neutral conditions on short time scales ($30 min) but yielded comparable results at longer time scales. Poor agreement was obtained under stable conditions for all models. Hence, for modeling event-based flux variations, forward models are preferred. Since the forward method requires detailed knowledge of ecophysiological, drag, radiative transfer and other canopy attributes, all of which are difficult to obtain on a routine basis, a symbiotic use of forward and inverse approaches is most advantageous.

Evaporation from three water bodies of different sizes and climates: Measurements and scaling analysis

“…where s is a relaxation time scale (defined as the ratio of turbulent kinetic energy to its dissipation rate), and C e is a similarity constant (see [46,47]). Hence, with these approximations, …”

Two-Dimensional Scalar Spectra in the Deeper Layers of a Dense and Uniform Model Canopy

“…Studies on scalar concentration (c) variability in a turbulent flow inside roughness elements are now receiving significant attention in many engineering and geoscience fields including atmospheric chemistry and pollution exposure, odour distribution and chemotactic algorithms in biological systems, contaminant dispersion inside urban areas, and biosphere-atmosphere CO 2 exchange near the soil surface inside tall canopies, to name a few (see Katul and Albertson 1999;Shraiman and Siggia 2000;Warhaft 2000;Finnigan 2000;Siqueira et al 2002;and Cheng and Castro 2002). The turbulent scales contributing to the variance in c are often examined using spectral (or structure function) analysis because such analysis can identify universal scaling laws or active eddy sizes responsible for the large c excursions.…”

The Turbulent Lagrangian Time Scale in Forest Canopies Constrained by Fluxes, Concentrations and Source Distributions

“…Vertical source/sink distributions of scalars in plant canopies have been estimated previously (Denmead 1991;Katul et al 1997;Leuning 2000;Leuning et al 2000;Siqueira et al 2002Siqueira et al , 2003Denmead et al 2005;Tiwary et al 2007) using measured vertical scalar concentration profiles combined with a prescribed turbulence dispersion field. Each of these studies used an assumed or calculated turbulent dispersion field to link the scalar source/sink distributions and the concentration profiles.…”

“…Each of these studies used an assumed or calculated turbulent dispersion field to link the scalar source/sink distributions and the concentration profiles. Large errors in the inferred sources/sinks can arise from uncertainties in knowledge of the dispersion field Siqueira et al 2002). This study aims to reduce this source of uncertainty in one class of dispersion model, the one-dimensional, Localised Near-Field (LNF) theory of Raupach (1989a,b).…”