Abstract
To investigate the characteristics of turbulence components above a hill evergreen forest canopy on a mountain slope, turbulence was measured over a forest in Northern Thailand. There were many trees taller than 30m. Each fluctuating component of the three–dimensional wind velocity(u, v, w)was analyzed using the eddy correlation method. The characteristic of turbulences were the occurrence probabilities of positive values in the fluctuating components, the skewnesses, the ratios of the standard deviation to the friction velocity(σu ⁄ u* , σv ⁄ u* , σw ⁄ u*), and the correlation coefficients among each fluctuation. We clarified the distributions of the characteristic of turbulence, and the relationships between atmospheric stability and each ratio of the standard deviation to the friction velocity.
The results showed there were wide distributions of the characteristics of turbulence, even in the neutral conditions(|(z−d)/L|<0.05). Distributions of the ratios of the standard deviation to the friction velocity were systematically categorized by the wind direction and the wind speed. An effect of a distance from a nearest tree was shown about σw ⁄ u* and σv ⁄ u* , but about σu ⁄ u* this tendency was weak. σw ⁄ u* in the weak wind was approximately 1.25 which was the character of general turbulence. σw ⁄ u* in the strong wind was different with each wind direction. The mean values and standard deviations were σu ⁄ u*=1.94±0.32, σv ⁄ u*=1.72±0.49, and σw ⁄ u*=1.31±0.22, respectively. σw ⁄ u* was corresponding to the value which had been observed on other canopies, but σu ⁄ u* was smaller than the value of short vegetation.
