Radiative and Nonlinear Influences on Orographic Gravity Wave Drag

Abstract

Vertical divergence of the mountain wave's momentum flux has recently been hypothesized to be an important contribution to the global momentum budget. Wavebreaking theories and envelope orography have been employed to explain the divergence of the momentum flux. Here, cloud-top radiational cooling is shown to locally destabilize the environment and disrupt the propagation of the mountain wave in idealized two-dimensional simulations, thus drastically altering the expected momentum flux profile. Also, simulations of two-dimensional mountain waves indicate that nonlinearities can increase the wave response if the lower layer is decoupled from the flow aloft or decrease the wave response by providing multiple reflection levels for the incident mountain wave. The onset of wavebreaking and the level at which the wave breaks can be influenced by the ambient thermodynamic profile.