| Summary: | An adjoint modeling system developed for the COAMPS nonhydrostatic model is used to explore the sensitivity of lee-side winds to the upstream atmospheric conditions for flow over a two-dimensional obstacle. For relatively small hills in the hydrostatic wave regime, the sensitivity patterns exhibit a dual lobed structure that is a manifestation of a superposition of internal gravity waves with downward-directed energy propagation. Nonhydrostatic waves generated by small terrain have corresponding sensitivities that are tilted vertically against the shear, which when introduced into the flow as perturbations, evolve into structures that resemble vertically decaying evanescent waves. Flow over higher obstacles near the gravity wave breaking threshold exhibits complex sensitivity patterns characterized by a wave-like packet of maxima and minima upstream of the middle- and upper-tropospheric region of wave breaking. In general, as the mountain height is increased, the tangent linear approximation becomes less accurate. However, the strongest nonlinearity occurs for flows very near the wave breaking threshold, rather than fully within the wave breaking regime forced by higher terrain.
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