Higher order turbulent statistics in plant canopies

Higher-order turbulent statistics were measured and modeled for several plant canopies. Measurements were taken at several sites, including at a 65 m tall, 400-600 year old coniferous temperate rain forest in Southern Washington. This site is a long-term AmeriFlux measurement site. At that site three-dimensional, sonic wind velocities and gas concentrations were measured at 10 Hz, 70 m and 3 m above the forest floor. These data were used to analyze second, third and fourth statistical moments of the turbulent quantities. These moments were also estimated using the Advanced Canopy-Atmosphere Simulation Algorithm (ACASA), which consists of a layered canopy radiation model, a physiological model for photosynthesis and stomatal control, a higher-order diabatic turbulence transport model (for longitudinal u and cross-wind v), and a soil mass and energy transport model. Model comparisons with measurements show this higher-order closure scheme yields reasonable results, although some errors are evident. The sensitivity to stability is examined, and comparisons also made for models and measurements for shorter canopies.