The Implications of Surface Heterogeneity and Mesoscale Variability on the Dynamics of Stable Atmospheric Boundary Layers

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This award provides funding for study of the stable atmospheric boundary layer (SABL), i.e. in situations of stable stratification resisting vertical displacement, with the goal of producing a deeper understanding of the dynamics and structure of turbulent flow and transport within this layer nearest the earth's surface. The researchers plan to accomplish this by exploring how the basic dynamics of the SABL are impacted by surface heterogeneity and mesoscale atmospheric variability. The work will be based on large eddy simulation (LES) type computer modeling using a numerical code and subgrid scale model that have been validated for stable flows. The planned research centers around obtaining answers to four main questions: (1) How is the turbulent kinetic energy (TKE) production-dissipation equilibrium altered by the roughness and thermal heterogeneities of the surface?; (2) Can horizontal transport of TKE produce much higher surface fluxes over areas with strong stability than would be expected under quiescent local conditions?; (3) How does mesoscale variability affect turbulence structure, production and transport in the SABL?; and (4) Do surface heterogeneity and/or mesoscale variability significantly increase SABL TKE levels, can they account for the extra turbulence needed to achieve closure in coarse-mesh (non-LES) models, and how can this information be integrated into such models? To pursue these topics, the researchers will simulate flows under conditions of varying mesoscale forcing and surface roughness characteristics, compute all terms of the TKE budget, and perform a proper orthogonal decomposition of the flow fields. The last step of the analysis will be to simultaneously include both surface heterogeneity and mesoscale variability in such simulations to explore their potential interactions.The intellectual merit of the work is centered on improved representation of idealized and controlled SABL conditions that the planned numerical experiments provide, which will in turn allow the researchers to study the effect of surface heterogeneity and mesoscale variability both separately and concurrently. This approach will allow a qualitative and quantitative understanding of the dynamics associated with these two building blocks on a numerical basis in ways that are extremely challenging to pursue from data-driven field experimental studies.The broader impacts of the research will include the education and training of a post-doctorate researcher and graduate student, as well as involvement of undergraduate and/or high school students in this research through an externally funded program. The work will benefit collaborators who are working to improve the representation of atmospheric boundary layers and land-atmosphere interactions in larger-scale atmospheric models, and potentially be relevant to researchers in fields from pollution dispersion to wind power generation.