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Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD) – The German Contribution

Subject Area Atmospheric Science
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 406980118
 
Final Report Year 2023

Final Report Abstract

This project is the German contribution to Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD), a project funded by the National Science Foundation (NSF) of the United States of America. The project aimed to understand the influence of heterogeneous ecosystems on the transport mechanisms of sensible and latent heat between the ecosystem and the atmosphere. Eddy covariance measurements are well suited to measure the turbulent sensible and latent heat fluxes between ecosystems and the atmosphere. The turbulent flux accounts for much of the transport in the atmospheric boundary layer (ABL), however, a systematic underestimation of fluxes of typically 10-30% has been found, resulting in a closure gap in the surface energy balance (SEB). The SEB gap is due in part to the fact that some of the sensible and latent heat is transported by secondary circulations (SCs), i.e., in the form of so-called advective and dispersive fluxes, and is therefore not captured by eddy covariance measurements. The characteristics of the SCs, and thus the magnitude of the advective and dispersive fluxes, in turn depend, among other things, on the heterogeneity of the surface. However, the exact relationships are not well understood. Therefore, the goal of this project was to explore the influence of surface heterogeneity on the transport mechanisms of sensible and latent heat in the ABL. In addition, since the measurement of advective and dispersive fluxes is very expensive, a parameterization should be developed to determine their flux contribution at eddy covariance stations. For this purpose, a measurement campaign with a large number of measurements was carried out on a 10 x 10 km2 area in northern Wisconsin (USA) in summer and fall 2019. The data collected during the measurement campaign were used to perform large-eddy simulations (LESs) as realistically as possible to investigate transport processes in the ABL. Idealized LESs were also performed to test the influence of different boundary conditions at the bottom of the model and for the development of the parameterization of the transport of heat by SCs. The model was tested on the eddy covariance measurements of the 17 stations and was shown to contribute to a significant reduction in the SEB gap.

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