Long-term measurements of biosphere–atmosphere exchange in complex terrain: By using state-of-the-art micrometeorological measurements at five reference sites in complex terrain (TERENO, ICOS), the overall ecosystem greenhouse gas balances (CO2, CH4, N2O) are investigated. With respect to homogeneity and stationarity, the micrometeorological conditions at monitoring field sites are often far from ideal and, therefore, the assessment of biosphere-atmosphere exchange over natural fragmented landscapes is still a great challenge. For reliable greenhouse gas budgets a comprehensive study of gap-filling and uncertainty assessment is required. In addition, a better understanding of source area (footprint) issues is important to understand the spatial aggregation of fluxes over complex terrain.
Energy Balance Closure: Worldwide in-situ measurement of the energy balance at >180 sites exhibit an underestimation of the turbulent transport (λE + H) by 10-30% measured by the eddy-covariance technique. There are strong indications (e.g. Stoy, Mauder, Foken et al., 2013) that heterogeneity-induced transport on large scales (100- 10000 m) is not captured by common eddy-covariance set-ups. Hence, the goal is capturing all relevant scales of biosphere-atmosphere exchange to address the enigmatic energy balance closure problem.
Large-eddy simulation: We apply the large-eddy simulation (LES) model PALM and develop new features to address specific research questions, such as virtual tower and lidar measurements and transport of greenhouse gases and air pollutants. This model serves as a tool for simulating tranport processes between biosphere and atmosphere on eco-system to the landscape scales. The results of these simulations form the basis to develop parameterizations of the impact of surface heterogeneities and complex terrain on the fluxes of energy and trace gases.