Turbulent Transport above a Mixed Northern Forest

The eddy-covariance (EC) method is often used to measure the exchange of chemical compounds such as CO2. Transport is calculated using the covariance of two high frequency measurements. There are problems with the EC method, particularly under light wind conditions. Surface-layer EC measurements represent relatively small flux footprints (~1Km). It is difficult to assess the representativeness of single-tower EC fluxes. In this paper, we compare NEE (net ecosystematmosphere exchange) of CO2 from two nearby sites in Wisconsin using the EC method. Different transport scales of CO2 are analyzed, and we propose and test a new parameterization of counter-gradient transport in the atmospheric surface layer over a forest canopy. The parameterization describes the observations very well. Finally, we discuss problems that occur under light wind and low turbulence conditions during the morning transition.