CAREER: A Universal Framework for Large-Eddy Simulation of Atmospheric Boundary Layer Flow Over Complex Terrain

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

The atmospheric boundary layer (ABL) directly influences human life through weather and air quality. Much remains to be understood about this thin atmospheric layer, partly because it is strongly affected by variations in topography and land-surface characteristics. These variations can lead to thermally-forced flow such as valley winds under calm conditions and atmospheric rotors and lee waves under strong winds with topographic blocking. Understanding the physical dynamics of such flow features requires detailed field observations and high-resolution numerical simulations. Large-eddy simulation (LES) is one of the most promising numerical techniques for modeling ABL flow because it allows control of turbulent length scales through spatial filtering to separate large, resolved motions from subfilter-scale, turbulent motions. Although primarily used for simulations of idealized flow conditions, LES has the potential to become universally applicable to ABL studies over complex terrain. Intellectual merit: This research will investigate key, innovative steps to extend the scalability of LES so it can be used from regional to very fine scales. This will allow LES to be effectively applied to flow over complex terrain and lead to greater insight into boundary layer flow processes. New strategies to control turbulent length scales, improve lateral boundary forcing, generate ensemble simulations, and reduce numerical errors due to subgrid surface roughness parameterizations and representation of steep topography will create a universal framework for general LES applications over complex terrain. This framework will be used together with observational data analysis to study terrain-induced flow features such as mountain waves and rotors and valley wind circulations. The PI has extensive prior experience with boundary layer flows over steep, mountainous terrain as well as with developing numerical methods and turbulence closure schemes for LES. An integrated education and outreach program is proposed to excite K-12 students and the general public about atmospheric boundary layer phenomena through an interactive modeling website and to provide numerical modeling experience to both undergraduate and graduate students. Students will participate in this public outreach program with UC Berkeley's Lawrence Hall of Science (LHS) through summer assistantships and a new graduate course on large-eddy simulation that will be directly coupled to the online exhibit. This course will also accelerate graduate research progress by providing hands-on training in numerical methods. Broader impacts: The proposed universal framework for LES will make possible seamless integration of flow features at all scales through nested simulations from the mesoscale to the urban scale. New knowledge of complex flows gained with this new numerical framework will dramatically improve models used to predict weather, air pollution, contaminant dispersion, and regional climate. Furthermore, insights into atmospheric circulations and intense gravity waves that can occur in mountainous areas will have important implications for aviation safety. New computational methods implemented in an advanced research numerical model will reach a broad community of users through continued public releases of code updates. Two graduate students will be trained through this research and two undergraduate research assistantships will be provided for under-represented minority engineering students through the SUPERB program at UC Berkeley. Research results will be disseminated through journal publications and conference presentations. The availability of the proposed educational tools will be advertised through the main Lawrence Hall of Science (LHS) website, through the PI's lab and department websites, and through an article in the Bulletin of the American Meteorological Society. The interactive modeling website has the potential to reach thousands of individuals and can be used in classroom settings at all age levels to introduce students to weather processes and numerical modeling. Hundreds of additional visitors, primarily K-12 students, will attend LHS museum floor demonstrations given by the PI and students.