Wave--mean-flow interaction is investigated through idealized modeling in which a barotropic synoptic-scale disturbance passes over an isolated three-dimensional mesoscale mountain. Atmospheres with constant static stability and cases with a jump in stability at the tropopause are considered. It is widely accepted that terrain-induced disturbances may have significant impact on the background flow, such as a global loss of momentum due to wave breaking. The simulations reveal that the stratosphere tends to induce wave breaking at the tropopause, which promotes wave--mean-flow interaction.

In addition to wave--mean-flow interaction induced by wave breaking, our results show that non-viscous processes may also have significant feedback to the large-scale flow. It is found that in the cases without wave breaking, the synoptic-scale flow undergoes a different time evolution due to the presence of the mountain. The influence of the mountain is assessed by performing a second simulation with the mountain removed, and examining the difference in dynamics between the two simulations. The differences reveal both global and local impacts, which are quantified by a domain-averaged momentum budget and the spatial distribution of the momentum difference fields, respectively.