Exchange processes in mountainous regions; Large-eddy-simulation

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Within this sub-project, high-resolution large-eddy simulations (LES) will be carried out in order to study the turbulent exchange within and between the forest and the overlying atmosphere. Compared with the experimental sub-projects of the bundle application EGER (ExchanGE processes in mountainous Regions), LES offers a complete and detailed insight into the threedimensional non-stationary turbulence field and allows the investigation of coherent structures and their effect on the vertical exchange and how they effect the turbulence measurements.In contrast with previous idealized studies, this sub-project aims to reproduce the measurement site conditions as close as possible. Topography will be included in the LES. The forest effect will be accounted for by coupling the LES with a detailed vegetation model, which calculates momentum, energy, and matter fluxes caused by the vegetation and provides it as boundary conditions for the LES. Large-scale driving forces will be provided by accompanying mesoscale simulations with WRF.Additionally, the critical size of forest gaps with respect to the generation of secondary circulations shall be determined by performing idealized studies with systematically varied gap size. LES data will be analyzed for coherent structures by advanced methods like linear stochastic estimation, empirical orthogonal functions (EOF), proper orthogonal decomposition (POD), and wavelet analysis. Also, virtual eddy-correlation measurements will be done for the sensor positions and footprints will be calculated for them using an LES embedded Lagrangian particle model.