Nonlinear mountain-wave generation, propagation, and dissipation is examined during the passage of an idealized barotropic synoptic-scale disturbance over an isolated three-dimensional mesoscale mountain. The waves and large-scale flow are simulated with a multiply nested nonhydrostatic model in a horizontally periodic domain. The mountain is initially located in a region of stagnant flow, so that mountain-wave development can be studied under realistic atmospheric conditions. Under the configuration of the synoptic scale flow in this study, there is both an accelerating phase and a decelerating phase of the incident flow.

Due to the transient incident wind upon the mountain range, the flow undergoes a transition from the low-level blocking/flow-splitting regime into nonlinear and linear wave regimes as the cross-mountain flow increases; the inverse progression is found as the cross-mountain flow decelerates back to zero. At the early stage of the accelerating phase, the flow is nonlinear, with lee vortex generation, followed by wake formation, vortex shedding, and finally wake detachment. As the incident flow further increases, the flow becomes more linear, and unsteady mountain wave propagation is present. After the maximum incident wind passes by the mountain, a transition from the linear regime to the nonlinear regime is found. During the decelerating phase, the low-level flow is deflected by the mountain and wake formation and lee vortex generation are again present.