Boundary layer effects on mountain gravity waves

Recent studies indicate that the existence of boundary layer modifies the characteristics of mountain gravity waves. A smooth boundary layer height profile over the mountain reduces the intensity of the mountain waves while steeper ones enhance them. In simulations with surface friction but no surface heat flux, the boundary layer depth is mainly determined by the profile of the vertical shear, through the generation of turbulent kinetic energy. In this study, we explore the three-dimensional structure of boundary layer depth over smooth and rough mountain profiles with surface heat and momentum fluxes. Emphasis is placed on conditions that lead to blocking. An attempt will be made to develop a relation between the gravity wave drag and the boundary layer height profile. One of the applications of this study is to refine the gravity wave drag parameterization for large-scale numerical models.