Canopy airflow and turbulence near the top of a forested ridge
Pavel Sedlak1, Katerina Potuznikova1, Radek Czerny2, Dalibor Janous2
1 Institute of Atmospheric Physics AS CR, Praha, Czech Republic
2 Institute of Systems Biology and Ecology AS CR, Brno, Czech Republic
2 Institute of Systems Biology and Ecology AS CR, Brno, Czech Republic
O 2.4 in Turbulence structure in and above forests
06.10.2009, 11:15-11:40, Kutschenhaus
Forest sites situated on a mountain ridge differ from the flat terrain sites in the structure of the canopy airflow and turbulence. This is important for assessing the contribution of advection to the trace gas budget and for analysis of the eddy flux footprint at such sites. The Experimental Ecological Study Site Bily Kriz in the Czech Republic is located near the top of a mountain ridge forested by a young Norway spruce plantation. Flow directions across the ridge (i.e. upslope or downslope) strongly prevail at the site. In addition to the standard single-point eddy covariance measurements above the canopy, vertical profiles of the flow velocity in the canopy were measured by sonic anemometers during an experimental campaign. Differences in the canopy flow characteristics as recorded when the site was on the upwind vs. downwind side of the ridge are described here.
In the “upwind” cases, vertical profiles of the studied characteristics (wind speed, skewness and kurtosis of the velocity components, u-w correlation coefficient) are similar to the profiles in flat terrain but they indicate somewhat enhanced efficiency of turbulence at transferring momentum deeper into the canopy. The “downwind” cases are characterized by much larger variability of the analyzed quantities, by intermittency of the flow direction and by lower efficiency of the momentum transfer down the canopy. Wavelet analysis was used for detection of characteristic temporal scale of coherent structures, their persistence and transfer effectiveness. First results for the typical cases of airflow over the ridge will be presented.
Full presentation file:
fp_O_2.4 (19.11.2009 14:14)