Gravity wave propagation through a vertically and horizontally inhomogeneous background wind

A 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 approximate to 70% and can also reduce reflection by up to approximate 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.