Effects of canopy morphology and thermal stability on turbulence spectra, structure functions and lagged two-point correlations observed inside a mixed hardwood forest

A year long field measurements using five 3-D sonic-anemometer-thermometers were carried out from June, 2004 to August, 2005 in a mixed hardwood forest at the University of Michigan Biological Station (UMBS) AmeriFlux site. Previously, we have reported that both thermal stability and seasonal changes in canopy morphology have significant influences on mean flow (secondary wind speed maximum and mean horizontal wind directional shear) and second-order velocity statistics, and on estimated eddy-diffusivity, mixing-lengths, zero-plane displacement height and drag coefficients used in various turbulence models of airflow in forest canopies.

In this presentation, we will discuss the influences of thermal stability and seasonal changes in canopy morphology on the characteristics of turbulence spectra and co-spectra, structure and co-structure functions, and lagged two-point correlation functions. Each of them has analytical and computational advantages and disadvantages in the depiction of turbulence time and length scales and spatial characteristics. The effects of horizontal mean wind directional shear observed inside this forest and the choice of coordinate on the characteristics of these single-point and two-point statistics are also discussed.