Gravity wave propagation through a vertically and horizontally inhomogeneous background wind

Abstract

AbstractA combination of ray theory and 2‐D time‐dependent simulations is used to investigate the linear effects of a time‐dependent, vertically, and horizontally inhomogeneous background horizontal wind field on the propagation, refraction, and reflection of small‐scale gravity wave packets. Interactions between propagating waves of different scales are likely to be numerous and important. We find that a static medium‐scale wave wind field of sufficient amplitude can channel and/or critical‐level filter a small‐scale wave or cause significant reflection, depending upon both waves' parameters. However, the inclusion of a time‐dependent phase progression of the medium‐scale wave can reduce energy loss through critical‐level filtering by up to ∼70% and can also reduce reflection by up to ∼60% for the cases simulated. We also find that the relative direction of propagation between the small‐scale and medium‐scale wave can significantly affect small‐scale wave filtering. When the phases are progressing in the same horizontal direction, the small‐scale wave is far more likely to become trapped and ultimately critical‐level filtered than if the phases are propagating in opposite horizontal directions unless reflection occurs first. Considerations of time‐dependent winds associated with medium‐scale‐propagating waves and their directionality are important for assessing the propagation and dispersion of small‐scale waves over large horizontal distances.