Predicting Scalar Source-Sink and Flux Distributions Within a Forest Canopy Using a 2-D Lagrangian Stochastic Dispersion Model

Abstract

This study proposes a two-dimensional Lagrangian stochastic dispersion model forestimating spatial and temporal variation of scalar sources, sinks, and fluxes withina forest canopy. Carbon dioxide and heat dispersion experiments were conducted forfield testing the model. These experiments also provided data for field testing a newlydeveloped one-dimensional Lagrangian analytical dispersion model. It was found that these two models produce similar scalar source-sinkand flux distribution patterns. Comparing with CO2 flux measurements, the one-dimensional model performed as well as the two-dimensional model even whenthe fetch is short (≈100 m). To drive these Lagrangian models, velocitystatistics through the canopy volume must be specified a priori. The sensitivity of thecomputed sources, sinks, and fluxes to the description of the flow statistics was furtherexamined. All in all, we found good agreement between model predicted andeddy-correlation measured CO2 and sensible heat fluxes.