A new approach in parameterisation of momentum transport inside and above forest canopy under neutral conditions

The forest as an underlying surface is often met in atmospheric models of different scales. Experimental evidence indicates that there is a significant departure of the wind profile within the forest and in the so-called transition layer above it. In the forest environment, the observed values are rather different than the values of 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. The validity of the proposed expressions was checked using the micrometeorological measurements from the two experimental sites: a) the Scots pine forest at Thetford, Norfolk, United Kingdom and b) the ponderosa pine forest at Shasta Experimental Forest, California, USA.