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

Dawn-to-dusk evolution of air turbulence, sensible heat and latent heat above a forest during cloud-free or near-cloud-free summer conditions is modelled by way of a system of differential equations. Temperatures in and above the canopy, near canopy-top wind velocities, early morning leaf moisture (dew) and afternoon canopy ventilation (Le. heat released 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, within-canopy temperature, and canopy-level radiation, turbulent fluxes and wind speeds Data were collected at a central New Brunswick mixed-wood forest site dominated by spruce (Picea spp.) and shade-tolerant hardwoods for four representative summer days. It was found that the effective canopy temperature was not only affected by insolation, but also by the extent of canopy ventilation and the amount of dew on the foliage. The growth of the mixing layer was affected hy canopy ventilation and by above-canopy wind speeds. Model calculations closely simulated the meteorological observations.