Average Winds Above and Within a Forest

This paper describes the results from a study of winds above and in a pine forest for a continuous period of 22 days. The winds are examined with reference to direction and time of day, that is, the effects of topography and atmospheric stability are considered. At night, when the atmosphere is stable, variations in profile shape above the forest are associated largely with site properties. During the day the variations are less, indicating that convective turbulence tends to control the profile shapes and to mask the effect of site irregularities. An examination of the power law provides tentative agreement with another study as well as with a model study. It is proposed that the ratio of the wind speed in the trunk space to the wind speed above the canopy is a measure of the magnitude of momentum transfer through the canopy. This ratio reaches a maximum at noon. At night the ratio drops to 75% of its daytime maximum value and displays a marked variation with direction.