Tracer validation of lagrangian analytic solution inside a forest canopy

A series of field experiments were conducted in 2002, 2004, and 2006 to collect data on turbulent dispersion inside a forest canopy. Perfluorocarbon tracers were released in several vertical and horizontal configurations and measured along with turbulence statistics above and below the canopy from a 30m tower. The data were used to test a recently developed two-dimensional Lagrangian analytic model. Four methods used to calculate these time scales from parameterizations and six different methods to derive them from observations were tested. Model results showed the best agreement with the tracer observations when the Lagrangian time scales calculated from the meteorological observations were used, although the performance substantially depended on the Lagrangian time scale parameterizations. The data also shows that the atmospheric stability has a substantial impact on turbulent diffusion because of its effect on the Lagrangian time scales. This effect is strongest during nighttime where the longer fetch causes the far-field effects to dominate. The data also show that the vertical variations of foliage have a significant effect on the Lagrangian time scales and therefore on transport and dispersion within the forest canopy.