Wind and turbulence properties within and above a slash pine forest in Florida and the effect of the atmospheric stability

The effects of the atmospheric stability on wind and turbulence properties within and above a slash pine forest are analyzed at the Florida AmeriFlux site near Gainesville, Florida. Measurements were conducted using 14 3-D sonic anemometers in May 2004. Several atmospheric stability parameters, i.e., h/L, Lc/L and Ls/L at tree top, are used and compared, where h, L, Lc and Ls are forest height, Monin-Obukov Length Scale, canopy penetration depth, and share length scale, respectively. At the studied site, Lc/L values are more or less similar to h/L values except in strong stable conditions, while Ls/L values are much smaller than h/L values. The wind speed decreases as the atmospheric stability becomes more stable or unstable at all levels, while the normalized wind speed u/u(h) increases with more stable conditions at all levels. Quadrant conditional analysis shows that stress contribution from quadrant 2 and 4 are higher than from quadrant 1 and 3 at most levels, and their ratio has its maximum at tree top and decreases as the atmosphere becomes more unstable (or stable), while the opposite happens at understory levels where positive covariance of u and w is observed. Normalized turbulence kinetic energy increases with more unstable (or stable) conditions. Different third moments are also analyzed against the atmospheric stability parameters.