Serafimovich, A*; Hübner, J; Eder, F; Falge, E; Foken, T: On the effect of forest edge on coherent structures above a forest canopy
Poster, 3rd iLEAPS Science Conference, Garmisch-Partenkirchen, Germany: 2011-09-18 - 2011-09-23

In the frame of EGER (ExchanGE processes in mountainous Regions) project the contribution of coherent structures to the vertical and horizontal transfer of energy and matter in a tall spruce canopy will be analyzed. The intensive observation period will be conducted in June - July 2011 at the FLUXNET site Weidenbrunnen Waldstein (DE-Bay), located in North-Eastern Bavaria in the Fichtelgebirge Mountains. Because of the wind throw by storm “Kyrill” in 2007 the large disturbed and deforested area appeared in the vicinity of the measuring site. The forest edge along this area will be investigated as a source of coherent structures which influence the exchange processes in the whole area and may be the reason for possible horizontal decoupling between forest and clear cut at day time on the lowest meters.

Observations of coherent structures will be obtained by a vertical profile of sonic anemometers equipped with fast carbon dioxide and water vapor analyzers deployed on the towers installed in deforested area, at the forest edge, and inside the forest. In addition three small masts will be set up in the trunk space of the forest and equipped with sonic anemometers forming with the towers the transects perpendicular and parallel to the forest edge.

To extract coherent structures from the turbulent time series, the technique based on the wavelet transform will be used. The Reynolds-averaged flux and flux contribution of coherent structures will be derived using a triple decomposition for the detected and conditionally averaged time series, when coherent structures are present. Using relational properties such as sweep and ejection ratios of coherent structures detected at the towers and the variations of the flux contribution with height, coupling processes between the subcanopy, canopy and air above the canopy level will be investigated. Combination of these results with measurements at the forest edge and over deforested area will be used to analyze the effect of the forest edge on the temporal scales of coherent structures and their role in flux transport and coupling processes between forest and deforested area. The obtained results are essential to improve the knowledge about the impact of forest heterogeneity on transport processes. Our contribution will present an overview of the experiment setup as well as first experimental results.

last modified 2011-09-27