Vertical and horizontal distribution of wind speed and air temperature in a dense vegetation canopy

Wind speed and temperature were measured within a corn row canopy to investigate horizontal and vertical variability of the mean wind speed and temperature. It appears that the mean wind speed can vary between 20% and 30% from its horizontal mean value. In the narrow row crop, the horizontal mean air temperature varies between 0.1°C (night-time) and 0.35°C (daytime) from the spatial mean value. Exceptions occur around noon in daytime when direct irradiation dominates and where the direct beam illuminates the within-row space of the canopy. Then, deviations of 1°C or more from the horizontal mean value are observed. Attention was focused on finding adequate scaling parameters of the within-canopy wind speed and air temperature profiles under various atmospheric stratification states. During daytime and night-time, the above-canopy friction velocity appears to be a good scaling parameter. Clear nights, however, are exceptions, when the above-crop wind speed drops to a very low value. Then, the within-canopy free convection velocity scale appears to be an appropriate scaling parameter for within-canopy processes. During daytime, the within-canopy temperature profiles scale well with the above-canopy temperature scale, T∗, for stationary irradiation and wind speed regimes. On calm nights, however, the relative within-canopy temperature profile scales very well with the within-canopy free convection temperature scale, Θ∗.