Lee waves

Illustration. The wind flows towards a mountain and produces a first oscillation (A) followed by more waves. the following waves will have lower amplitude because of the natural damping. Lenticular clouds stuck on top of the flow (A) and (B) will appear, immobile despite the strong wind.

Same phenomena but a second mountain is placed a about one wavelength from the first one. A resonance occurs and the second oscillation has a greater amplitude than the first one. When there is no more moutain to excitate the oscillations, a damping starts to appear and the following oscillation amplitudes will be lower.