Fluid Mechanics of Airflow over Hills: Turbulence, Fluxes, and Waves in the Boundary Layer

Abstract

Recent developments in the understanding of turbulent airflow over hills and complex terrain are described. We first review linear calculations for the mean flow over isolated hills including the effects of different wind and stratification profiles upstream, and variations in surface roughness. This approach is extended to model flow over complex terrain and is contrasted with other numerical developments. The turbulence structure is also examined with a simple linear approach that is used to calculate how length scales, variances, and spectra vary over hills. More sophisticated modeling is required near the top of the inner layer where rapid distortion, curvature, and nonlinear interaction all combine in determining the structure. Finally, we discuss the dispersion and deposition of particles over hills, considering both thin plumes and plumes far from their source that are well mixed in the boundary layer.