A simple three-dimensional canopy – planetary boundary layer simulation model for scalar concentrations and fluxes

Abstract

We present a numerical model capable of computing the physical processes within both plant canopy and planetary boundary layer (PBL), offering the potential benefit of wide applicability due to reduced computational requirements. The model, named SCADIS (scalar distribution), synthesizes existing knowledge of boundary and surface layer turbulence and surface layer vegetative processes and was tested using several data sets from the European part of Russia and Siberia obtained as part of the EUROSIBERIAN CARBONFLUX project. Despite simplifications which were necessary in order to simulate the natural processes, the first version of the model presented here demonstrated a satisfactory agreement between modelled and observed data for different surface features and weather conditions. For example, the model successfully predicted the diurnal patterns of concentration profiles of CO2, water vapour and potential temperature profiles both within the summer atmospheric boundary layer and within the plant canopy itself. The very different effects of the surface energy characteristics of bog versus forest on convective boundary layer (CBL) structure and development are also illustrated. The model was applied to evaluate the effective footprints for eddy covariance measurements above non-uniform plant canopies, the case study here being a mixed spruce forest in European Russia. The model also demonstrates the likely variations in the above-canopy turbulence and surface layer fluxes as dependent on the presence of patches of deciduous broadleaf forest within a predominantly evergreen coniferous stand.