Spatially and Temporally Varying Flow and Turbulence in the Atmospheric Boundary Layer

Abstract

Spatial and temporal variations of buoyancy are ubiquitous in geophysical and environmental flows, and they have a fundamental impact on the dynamics of the Atmospheric Boundary Layer (ABL). In this dissertation, we conduct observational analyses, theoretical modeling, and numerical experiments to elucidate these dynamics. In Chapter 2, we develop approaches to detect and classify intermittent regimes under stable static stratification, examine how the turbulent bursts are generated and advected, and offer guidance on representing such regimes in geophysical closure models. The findings have the potential to advance weather forecasting and climate modeling, particularly in the all-important polar regions, thus opening new pathways for improved parametrizations in coarse atmospheric models. The non-dimensional statistical parameters identified in Chapter 2 are found to be critical in describing the turbulent content and activity range of turbulent kinetic energy (TKE) time series, and this motivates investigating the probability law of TKE for diabatic Atmospheric Surface Layer (ASL) flows under different stability conditions. Hence, in Chapter 3, we establish that TKE obeys a gamma (γ) probability density function, and then develop and successfully test a nonlinear Langevin equation model that encodes a linear relaxation of TKE to its mean state. The three parameters needed to describe the drift and nonlinear diffusion terms can all be determined from the ground shear stress and the mean velocity at the corresponding height. We then shift our attention to spatial variability since earth surface heterogeneity induces spatial variations in buoyancy that can drive secondary circulations. In Chapter 4, we focus on the influence of synoptic wind on coastal circulation dynamics using large eddy simulations (LES). Scaling analysis that relates the shore mass and thermal exchange internal parameters to the external parameters results in a power law that governs their interdependence. In Chapter 5, we simulate the unsteady problem of Chapter 4, where the resultant land-sea breeze thermal circulations (LSBs) are explored, and non-equilibrium conditions are assessed. The resultant LSBs are classified using k-means methods in both Chapters 4 and 5. Finally, in Chapter 6, conclusions and implications to the whole dissertation are provided.