A Study Of Turbulence And Dispersion In The Atmospheric Boundary Layer Above Heterogeneous Land Surfaces

The major objective of this study was to better understand the physical mechanisms involved in the dispersion of materials in the ABL that develops above heterogeneous land surfaces, using large eddy simulations This project consisted of three tasks: (i) An evaluation of our LES model against observations; (ii) A systematic analysis of the impact of microscale and meso-scale heat patches and topographical features on the structure of the ABL; and (iii) An analysis of the impact of these landscape heterogeneities on the dispersion of materials in the ABL. All three tasks have been fully completed. Using radiosondes, a network of surface fluxes. and a volume imaging lidar deployed in FIFE, we showed that, overall, the LES model performs quite well. However, its subgrid-scale parameterization needs to be improved to increase eddy dissipation. Various simulations using the FIFE data sets as well as ideal conditions indicate that microscale heterogeneities of surface heat fluxes and topographical features have only a minor to modest impact on the CBL, but can significantly affect the structure of turbulence. Meso-scale heterogeneities not only affect the structure of turbulence, but they can also significantly affect the mean characteristics of the CBL. These heterogeneities can also significantly affect the dispersion of materials. The results of this research were published in major peer-reviewed journals, and were presented at various professional meetings. A fourth and last year of funding was also provided to make a preliminary analysis of the ability of RAMS to simulate the stable nocturnal boundary layer (SNBL), in preparation of a more complete study on the dispersion of materials in this type of boundary layer. which will be proposed as a continuation of this completed project.