56 Turbulence structure under drainage flow within a sloped forest canopy

Monday, 20 June 2016
Eric S. Russell, Washington State University, Pullman, WA; and Z. Gao and H. Liu

The objective of this work is to study the drainage flow within a forested canopy and its effect upon the micrometeorological fields, its development, and the stability of the flow. The transition from the daytime upslope flow to nocturnal downslope flow was determined and its connection to biophysical and micrometeorological effects within the canopy was detailed. Here we used data collected from a single multi-level tower within a mixed northern forest canopy sub-layer. After looking at the controls of the drainage flow through the canopy layer, we attempted to determine the stability of the flow classifying it as stable or unstable. Unstable downslope flow (~40% of the downslope periods) held significantly higher turbulence levels compared to stable periods while upslope flow never fell under the unstable flow conditions. From these classifications, we examined the impact of the flow stability upon the turbulence characteristics and its structure. Structural comparisons were made using wavelet transforms to look at the size and impacts of eddies within the canopy sub-layer on the total canopy characteristics.
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