Modelling vegetation-atmosphere CO2 exchange by a coupled Eulerian-Langrangian approach

A Eulerian-Lagrangian canopy microclimate model was developed with the aim of discerning physical from biophysical controls of CO2 and H2O fluxes. The model couples radiation attenuation with mass, energy, and momentum exchan ge at different canopy levels. A unique feature of the model is its ability to combine higher order Eulerian closure approaches that compute velocity statistics with Lagrangian scalar dispersion approaches within the canopy v olume. Explicit accounting for within-canopy CO2, H2O, and heat storage is resolved by considering non-steadiness in mean scalar concentration and tem perature. A seven-day experiment was conducted in August 1998 to investigat e whether the proposed model can reproduce temporal evolution of scalar (CO 2, H2O and heat) fluxes, sources and sinks, and concentration profiles with in and above a uniform 15-year old pine forest. The model reproduced well t he measured depth-averaged canopy surface temperature, CO2 and H2O concentr ation profiles within the canopy volume, CO2 storage flux, net radiation ab ove the canopy, and heat and mass fluxes above the canopy, as well as the v elocity statistics near the canopy-atmosphere interface. Implications for s caling measured leaf-level biophysical functions to ecosystem scale are als o discussed.