Comparison of conventional Lagrangian stochastic footprint models against LES driven footprint estimates

摘要

In this study we introduce a comparison method for footprint model resultsby evaluating the performance of conventional Lagrangian stochastic (LS) footprintmodels that use parameterised flow field characteristics with results of a Lagrangiantrajectory model embedded in a large eddy simulation (LES) framework. The two conventional models followthe particles backward and forward in time while the trajectories in LES onlyevolve forward in time. We assess their performance in two unstably stratified boundary layersat observation levels covering the whole depth of the atmospheric boundary layer.We present a concept for footprint model comparison that can be applied for 2-Dfootprints and demonstrate that comparison of only cross wind integratedfootprints is not sufficient for purposes facilitating two dimensional footprint information.Because the flow field description among the three models is most realisticin LES we use those results as the reference in the comparison.We found that the agreement of the two conventional models against the LESis generally better for intermediate measurement heights and for the moreunstable case, whereas the two conventional flux footprint models agree bestunder less unstable conditions. The model comparison in 2-D was found quitesensitive to the grid resolution.