Abstract
The number of studies evaluating flux or concentration footprints has grown considerably in recent years. These footprints are vital to understand surface–atmosphere flux measurements, for example by eddy covariance. The newly developed backwards trajectory model LaStTraM (Lagrangian Stochastic Trajectory Model) is a post-processing tool, which uses simulation results of the holistic 3D microclimate model ENVI-met as input. The probability distribution of the particles is calculated using the Lagrangian Stochastic method. Combining LaStTraM with ENVI-met should allow us to simulate flux and concentration footprints in complex urban environments. Applications and evaluations were conducted through a comparison with the commonly used 2D models Kormann Meixner and Flux Footprint Predictions in two different meteorological cases (stable, unstable) and in three different detector heights. LaStTraM is capable of reproducing the results of the commonly used 2D models with high accuracy. In addition to the comparison with common footprint models, studies with a simple heterogeneous and a realistic, more complex model domain are presented. All examples show plausible results, thus demonstrating LaStTraM’s potential for the reliable calculation of footprints in homogeneous and heterogenous areas.
Highlights
Several models have been published since the 1990s which can be distinguished into four categories: (1) analytical models [7,8,9,10,11,12]; (2) Lagrangian stochastic particle dispersion models (LS) [13,14]; (3) large-eddy simulations (LES) [15,16,17]; and (4) closure models [18,19,20]
To evaluate the performance of LaStTraM, the results of the homogeneous model area are compared against the Flux Footprint Predictions model (FFP) model and the Kormann–Meixner model (K–M)-model
The evaluation of the ENVI-met based footprint simulation LaStTraM with two wellknown models, an analytical model and a model that is based on a Lagrangian model [9,11], demonstrates that the modeled footprints are comparable for detector heights of 3 m, 20 m, and 40 m in stable and unstable conditions despite the structural differences of the models
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Atmospheric stability, wind speed and direction, as well as turbulent intensity are atmospheric factors influencing the footprint For this purpose, several models have been published since the 1990s which can be distinguished into four categories: (1) analytical models [7,8,9,10,11,12];. ENVI-met features a sophisticated plant physiology stomata model (A-gs; [22]) to simulate transpiration and carbon uptake of plants, the influences of heterogeneous sources and source distributions (e.g., trees, shrubs, grass) on the footprint can be modelled in complex topographies (e.g., within dense and complex urban areas) [23,24]. The influence of heterogeneous sources in more complex model areas on the concentration and the flux footprint is discussed
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