Staudt, K*; Falge, E; Serafimovich, A; Pyles, RD; Foken, T: Modeling the exchange of energy and matter within and above a spruce forest site with ACASA
Vortrag, Atmospheric Transport and Chemistry in Forest Ecosystems, Thurnau: 05.10.2009 - 08.10.2009

Within the EGER project, the exchange of energy and matter between the soil, the vegetation and the atmosphere at the spruce forest site Waldstein-Weidenbrunnen in the Fichtelgebirge mountains in northern Bavaria, Germany, was modeled with the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA). ACASA is a multilayer canopy-surface-layer model that incorporates a third-order closure method to calculate turbulent transfer within and above the canopy and was developed at the University of California, Davis. Comprehensive micrometeorological and plant physiological measurements were performed during the two intensive observation periods of the EGER project in autumn 2007 and summer 2008, such as measurements of in- and above canopy profiles of standard meteorological parameters and eddy covariance measurements at six heights on a 36 m high tower observing the turbulence structure within and above the forest. This data base allowed us to extensively test the ability of the ACASA model to simulate the exchange of energy and matter at our site. In a first step, a sensitivity analysis of the ACASA model using the generalized likelihood uncertainty estimation (GLUE) methodology was performed, considering fluxes above the canopy. It appeared that the model was only strongly sensitive to a few of the input parameters, whereas for many parameters equifinality was observed, a common problem of complex SVAT models. However, the calculation of uncertainty bounds demonstrated that the ACASA model was able to reproduce all above-canopy fluxes well. For two fair weather periods not only fluxes above the canopy but also profiles of water vapor fluxes within the canopy were compared to eddy-covariance measurements. Thereby, the contribution of coherent structures to the fluxes was accounted for and the ability of the ACASA model to cover these contributions investigated. ACASA was capable of reproducing the shape of the profiles of water vapor fluxes within the canopy well. In general, the profiles were in good agreement for coupled and partly coupled exchange regimes, whereas during decoupled situations modeled and measured values were less consistent.

Letzte Änderung 26.10.2009