Wind profile within the forest canopy and in the transition layer above it

Abstract

The forest as an underlying surface has to be considered in atmospheric models of different scales. Experimental evidence shows that there can be a significant variation of the wind profile within the forest and in the so-called transition layer above it. Experimentally observed wind speed is often found below as indicated by the wind speed profile obtained by: (a) the logarithmic relationship in the transition layer and (b) K theory within the forest. This situation can seriously disturb the real physical picture concerning the transfer of momentum, heat and water vapour from the surface into the atmosphere. In order to minimise the foregoing problems, we have suggested an empirical expression for the wind profile in the transition layer above the forest as well as the expressions for the wind profile and turbulent momentum transfer coefficient within the forest canopy layer. Additionally, for the proposed wind profiles, the expressions for the displacement height, roughness length and parameters are determined as functions of the forest structural characteristics using continuity conditions and a simple mass conservation hypothesis. The validity of the proposed expressions was checked using the micrometeorological measurements from the experimental sites in the Thetford Scots pine forest in Norfolk, United Kingdom and in the Ponderosa pine forest at the Shasta Experimental Forest, California, USA. © 2002 Elsevier Ltd. All rights reserved.