Investigations with a higher-order canopy turbulence model into mean source-sink levels and bulk canopy resistances

Abstract

The legitimacy of using bulk aerodynamic and canopy resistances in surface energy budget equations is examined in this paper. Specifically, the variation of the effective source heights for momentum, water vapor, and heat is analyzed by estimating zero plane displacements for a modeled soya bean canopy, when model leaf surface resistances are changed, causing varying stability conditions. Also, the changes in bulk canopy resistances are examined as a function of the leaf surface resistances. The model used is a linked soil-plant-atmosphere model based on higher-order closure principles. The model confirms previous reports of major soil contributions to evapotranspiration under certain conditions. The erratic behavior of the zero plane displacements for water vapor and heat as a function of leaf surface resistance demonstrates that the concept of a single effective source-sink height is not easily applied to plant canopies. The zero plane displacement for momentum was found to be consistent with previous results, independent of leaf surface resistance. Canopy resistance changes qualitatively match leaf surface resistance changes, but quantitative differences can be large. The canopy resistance changes less quickly than the leaf surface resistance even when soil evaporation is not a factor.