Seasonal Variation of Turbulence Characteristics in and above a Mixed Hardwood Forest Observed at the UMBS AmeriFlux Site

Field tower-based observations of turbulent velocity and temperature using 3-D CSAT3 sonic-anemometer-thermometers and thermocouples at seven levels from the ground to 2.4 times canopy height were carried out at the University of Michigan Biological Station AmeriFlux site from summer 2004 to fall 2005. A suite of statistical analyses that have been previously applied to tower-based observations of canopy airflow are performed to this long-term data set. These include vertical profiles of mean and higher-order moments, spectra and cospectra, eddy-diffusivity, drag coefficients, Eulerian time scales. The first goal is to examine the diurnal and seasonal variability of in-canopy turbulence in terms of stability and seasonal variation of foliage density. A secondary goal is to examine if there is a better alternative turbulent parameter to the friction velocity measured above the canopy for filtering nighttime eddy-covariance measurement of CO2 fluxes.