While net ecosystem exchange (NEE) of carbon dioxide is routinely measured at numerous sites, recent research has questioned how to interpret NEE from eddy covariance measurements, particularly in areas of complex terrain. Much of this research has focused on vertical advection resulting from thermally-driven horizontal flow divergence.

This paper examines horizontal and vertical advection and gully flows at Morgan-Monroe State Forest, Indiana (39° 19' N, 86° 25' W). Evidence of non-zero vertical velocities at two heights above the forest canopy, and flow divergence is presented. Correlations with radiative loss and other parameters suggest that divergence is driven by local circulations, such as katabatic drainage flows. A small (8-m) mast was installed and instrumented with sonic anemometers and thermocouples, to examine various aspects of flow in a gully below the forest canopy. These included diurnal trends as well as forcing conditions for thermally driven or dynamically driven gully flows.

Preliminary results indicate that the three-dimensional flow structure here is more complex than in non-forested gully flow, and support the suggestion that the inclusion of a simple vertical advection/divergence term in calculations of NEE, based on above-canopy measurements, is not generally applicable.