TurbEFA: an interdisciplinary effort to investigate the turbulent flow across a forest clearing

the atmosphere within turbulence closure models is mainly limited by a realistic three-dimensional (3D) representation of the vegetation architecture. Within this contribution we present a method to record the 3D vegetation structure and to use this information to derive model parameters that are suitable for numerical flow models. A mixed conifer forest stand around a clearing was scanned and represented by a dense 3D point cloud applying a terrestrial laser scanner. Thus, the plant area density (PAD) with a resolution of one cubic meter was provided for analysis and for numerical simulations. Multi-level high-frequency wind velocity measurements were recorded simultaneously by 27 ultrasonic anemometers on 4 towers for a period of one year. The relationship between wind speed, Reynolds stress and PAD was investigated and a parametrization of the drag coefficient CD by the PAD is suggested. The derived 3D vegetation model and a simpler model (based on classical forest assessments of the site) were applied in a boundary layer model (BLM) and in large-eddy simulations (LES). The spatial development of the turbulent flow over the clearing is further demonstrated by the results of a wind tunnel experiment. The project showed, that the simulation results were improved significantly by the usage of realistic vegetation models. 3D simulations are necessary to depict the influence of heterogeneous canopies on the turbulent flow. Whereas we found limits for the mapping of the vegetation structure within the wind tunnel, there is a considerable potential for numerical simulations. The field measurements and the LES gave new insight into the turbulent flow in the vicinity and across the clearing. The results show that the zones of intensive turbulence development can not be restricted to the locations found in previous studies with more idealized canopies

TurbEFA: Ein interdisziplinärer Ansatz zur Untersuchung der turbulenten Strömung an einer Waldlichtung

Waldökosysteme spielen eine bedeutende Rolle in der Interaktion zwischen Landoberfläche und Atmosphäre. Ein besseres Verständnis der Austauschprozesse ist unter anderem notwendig für eine Einschätzung der Absorption und Emission von Spurenstoffen (z.B. CO2) und der Risiken von Waldschäden durch Wind, Frost und Dürre. Heutige Studien zur Rolle von terrestrischen Ökosystemen im Wasser- und Kohlenstoffkreislauf basieren auf langfristigen Messungen des Energie- und Massenaustausches zwischen Vegetation und Atmosphäre durch die Eddy-Kovarianz Methode (Goulden et al. 1996). Mehr als 500 Standorte weltweit sind derzeit in FLUXNET organisiert, einem internationalen Netzwerk (Baldocchi et al. 2001) zur kontinuierliche Messungen des Stoff- und Energieaustausches nach standardisierten Methoden (Aubinet et al. 2000). Der Austausch von Waldökosystemen wird dabei an einem Messturm durch eine Punktmessung über dem Bestand bestimmt, die eine bestimmte häufig komplexe Quellfläche repräsentiert. Mehr als drei Dekaden der Forschung in Feldexperimenten und Modellierung haben gezeigt, dass verbleibende Unsicherheiten vor allem durch räumliche Inhomogenität des Austausches begründet sind. Insbesondere fehlen Ansätze für eine geeignete Parametrisierung dieser Inhomogenitäten in numerischen Modellen

Calculating advective fluxes in tall canopies – Towards better wind speed distribution using 3D vegetation scans in high resolution

The wind speed distribution in forests is dominated by inhomogeneities like step changes in stand height and forest clearings. Thus a major limitation in the attempts to describe and model the wind field in destined tall canopies is the parameterization of plant architecture. The relationship between wind speed, drag coefficient and plant area distribution was experimentally investigated in a mixed conifer forests in the lower ranges of the Osterzgebirge. The results of this study will be applied to different kinds of flow models to investigate the influence of advective fluxes of energy and matter. From May 2008 to May 2009 intensive turbulence measurements took place on a transect over the forest clearing „Wildacker“ (Tharandter Wald, N 50°57'49", E 13°34'01"). In total 25 measurement points, at 4 towers (heights: 40m, 40m, 40m, 30m) including five at ground level position (2 m), are used to record the turbulent flow simultaneously. Terrestrial laser scanning is a fast developing tool and appears to be an efficient method to record 3D models of the vegetation. The forest stands around the clearing (500 m x 60 m) were scanned applying a Riegl LMS-Z 420i and a Faro LSHE880. Thereby scans from different ground positions and from the top of the main tower (height: 40m) were done. The scans were filtered and combined to a single 3D representation of the stands. The detection of trees was done automatically and mean tree distances were calculated. The 3D point cloud of trees in a 60m x 310m x 50m model domain was transformed into a 3D voxel space. The normalized point density of each voxel represents the plant area density PAD. A scaling of the laser derived totals per floor space was done by measurements with the LAI2000 (LICOR). The so calculated PAD and the spatial arrangement of points inside the voxel can be used to derive a parameterization for the drag coefficients. Simultaneously, the drag coefficients are calculated from turbulence measurements at the positions of anemometers. Finally the dependency between drag coefficients and PAD can be investigated with respect to stability and wind speed. Using measured wind profiles this study aims further to validate and develop estimates of parameters like mixing length, displacement height and roughness length from the plant area density profile

Development and Application of Functionalized Protein Binders in Multicellular Organisms

Protein-protein interactions are crucial to almost all biological processes. Studying such interactions in their native environment is critical but not easy to perform. Recently developed genetically encoded protein binders were shown to function inside living cells. These molecules offer a new, direct way to assess protein function, distribution and dynamics in vivo. A widely used protein binder scaffold are the so-called nanobodies, which are derived from the variable domain of camelid heavy-chain antibodies. Another commonly used scaffold, the DARPins, is based on Ankyrin repeats. In this review, we highlight how these binders can be functionalized in order to study proteins in vivo during the development of multicellular organisms. It is to be anticipated that many more applications for such synthetic protein binders will be developed in the near future