Link P.A., Improving Parameterization of Scalar Transport through Vegetation in a Coupled Ecosystem-Atmosphere Model. PhD Thesis, VU University, Amsterdam, The Netherlands.
Abstract:
Several regional-scale ecosystem models currently parameterize subcanopy
scalar transport using a rough-wall boundary eddy diffusivity formulation. This
formulation predicts unreasonably high soil evaporation beneath tall, dense forests
and low soil evaporation beneath short, sparse grass. This study investigates
alternative formulations by reviewing literature on flow and scalar transport in
canopies, taking field measurements of subcanopy latent heat flux, and testing
alternative model formulations in constrained numerical experiments. A field
campaign was conducted in a dense rainforest in Luquillo National Forest, Puerto
Rico, to measure wind and fluxes with eddy covariance devices. Wind velocities and
fluxes of latent heat, sensible heat, and momentum were found to be much smaller
below the canopy than above it. Modeling experiments tested a mixing-layer-based
formulation of eddy diffusivity and a soil evaporation cutoff based on vortex
penetration depth. The vortex penetration cutoff was found to be the most
physically accurate and computationally simple option, and this study recommends
that ecosystem and land-surface models adopt this formulation for subcanopy scalar
transport.