A large-eddy simulation study of atmospheric boundary layer influence on stratified flows over terrain

The onset of internal gravity wave breaking and leeside flow response regimes of trapped lee waves and nonlinear breakdown (or hydraulic-jump-like state) as they depend on the classical inverse Froude number, Fr⁻¹ = Nh/Ug, is explored in detail.

Here, N is the Brunt-Väisälä frequency, h is the hill height, and Ug is the geostrophic wind. The results here demonstrate that the presence of a turbulent ABL influences mountain wave (MW) development in critical aspects, such as dissipation of trapped lee waves and amplified stagnation zone turbulence through Kelvin-Helmholtz instability. It is shown that the nature of interactions between the large-scale flow and the ABL is better characterized by a proposed inverse compensated Froude number, Fr⁻¹ = N(h − zi)/Ug, where zi is the ABL height.