DAWN-TO-DUSK EVOLUTION OF AIR TURBULENCE, TEMPERATURE AND SENSIBLE AND LATENT-HEAT FLUXES ABOVE A FOREST CANOPY - CONCEPTS, MODEL AND FIELDCOMPARISONS

Dawn-to-dusk evolution of air turbulence, sensible heat and latent hea t above a forest during cloud-free or near-cloud-free summer condition s is modelled by way of a system of differential equations. Temperatur es in and above the canopy, near canopy-top wind velocities, early mor ning leaf moisture (dew) and afternoon canopy ventilation (Le. heat re leased from the canopy and from below the canopy) are included in the mathematical treatment. Computed results are compared with field data for atmospheric temperature and wind speed profiles up to 1200 m, with in-canopy temperature, and canopy-level radiation, turbulent fluxes an d wind speeds Data were collected at a central New Brunswick mixed-woo d forest site dominated by spruce (Picea spp.) and shade-tolerant hard woods for four representative summer days. It was found that the effec tive canopy temperature was not only affected by insolation, but also by the extent of canopy ventilation and the amount of dew on the folia ge. The growth of the mixing layer was affected hy canopy ventilation and by above-canopy wind speeds. Model calculations closely simulated the meteorological observations.