| Popis: |
It is well established that the transfer of heat and matter across the interfacial sublayer in the immediate vicinity of any surface is strongly controlled and limited by molecular transfer properties. Whereas a considerable part of the shear stress is transmitted to the surface as a form drag on the individual asperities. The sublayer-Stanton number, B i , can be considered as a measure of the difference in the corresponding rates of momentum and heat as well as matter to and from surfaces, no matter how irregular they may be. This quantity plays, therefore, an important role in modelling the exchange of heat and matter between the atmosphere and the vegetation-soil system and natural water systems, respectively, and, hence, in deriving surface fluxes of sensible and latent heat by remote sensing techniques. Usually, B i is related to the ratio z 0, z p, where z 0 is the roughness length for momentum, and z p is that for heat and matter, respectively. It is argued that the derivation of this relationship is not straight-forward. Instead, a more physically adequate relationship is presented. Sublayer-Stanton numbers of heat and matter for different types of surfaces are presented and discussed. The results are derived from the vertical profile data of wind speed, temperature, humidity and HN03 concentrations, collected during the GREIV 1 1974 project and the experiment "ecosystem wheat" of the EUROTRAC subproject BIATEX, and from model studies for aerodynamically smooth surfaces. The model results for aerodynamically smooth surfaces are based on Roth's (1972) modified Heisenberg model for the spectral energy transfer under locally isotropic conditions. These results are compared with those provided by Reichardt's (1951) approach for an effective diffusivity. The B i (exp - 1)-values obtained from the field and the model studies are much larger than those suggested by Garratt and Hicks (1973). |
