The stationary response to large-scale orography in a general circulation model and a linear model

The linear model's response to a Gaussian mountain at 45°N latitude is dominated by a single wave train radiating toward the southeast. For mountain heights between 0.7 and 2 km, the GCM's stationary waves are similar to the linear model response to orography, although amplitudes increase less rapidly than linearly with mountain height. For larger mountains, closed isentropes and distinctly nonlinear flow occur along the surface of the mountain and a large poleward-radiating wave train develops. The development of closed isentropes, and the breakdown of linear theory, can be predicted whenever the slope of the surface exceeds the slope of the isentropes in the unperturbed (no mountain) basic state. -from Authors