Effects of upstream boundary layer turbulence on mountain waves

Large-eddy simulation is used to examine the role of boundary layer turbulence on the evolution and dynamics of mountain waves. Our focus is on high amplitude mountain waves that are enhanced by a self-induced critical layer and generate a strong down slope wind component. Simulations are presented for a range of upstream boundary layer depths and surface heating. Results show that for weak heating, upstream turbulence modifies the leeside flow structure, but does not change the overall strength of the down slope winds. The flow in these cases is very similar to free slip, unheated results. Increased heating rates leads to a deeper down slope wind maximum with a significant increase in the boundary layer depth on the leeside of the mountain ridge. As upstream heating becomes more extreme, boundary layer growth reduces the strength of the mountain wave response. Strong upstream turbulence also affects the self-induced critical level, eventually preventing critical layer reflection and wave amplification.