Turbulence in the Long-lived, Very Stable Atmospheric Boundary Layer

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Stable conditions of the atmosphere are frequently observed during nighttime in mountainous terrain or during cold seasons over land. Stable conditions persist for days as a long-lived weather regime in polar regions. A better understanding of atmospheric flows under stable conditions is key for advances in areas such as mass balance of polar ice sheets, climate modeling, orographic precipitation, fog formation, severe downslope windstorms, and associated aircraft turbulence. Despite numerous theoretical, computational, and experimental investigations of stable conditions in the atmosphere, its accurate representation in numerical weather prediction (NWP) models remains to be a challenging task. Over or under estimation of turbulent mixing is known to create unintended consequences in other aspects of meteorological modeling, such as incorrect predictions of stronger winds and precipitation. This project aims to better comprehend turbulence in long-lived, stable conditions and develop a reliable theory for its mathematical representation in computer models, which is expected to pave the way to more accurate weather forecasts and climate projections with reduced uncertainties. The scientific objectives of the project will be achieved through intensive direct numerical simulations of turbulence in the Ekman layer under the joint action of a surface cooling flux and a constant ambient stratification. The configuration is an idealization of long-lived atmospheric boundary layers observed in polar regions and differs from the common approach of simulating stable Ekman layers with surface cooling only. The project will quantify the effects of an expanded dimensionless parameter space on turbulence. The project will extend and refine similarity theories and correlations for long-lived stable Ekman layers. A quantitative classification scheme to account for the global intermittency of turbulence in stable boundary layers is expected at projection completion. This project will contribute an atmospheric boundary layer module to an existing open source spectral/hp element flow solver and provide research experiences in computational sciences and high-performance computing to undergraduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.