Abstract

In the first part of this talk, orographic gravity-wave breaking in flows with directional wind shear is investigated using numerical simulations of idealized, nearly hydrostatic, atmospheric flows over an axisymmetric isolated mountain. These simulations, which use the WRF -ARW atmospheric model, differ in degree of flow non-linearity and shear intensity. The aim is to diagnose the conditions for mountain wave breaking based on large-scale variables (i.e. wind shear and terrain elevation). A regime diagram describing the wave breaking behaviour in Richardson number–dimensionless mountain height parameter space is presented.

In the second part of the talk, mountain wave turbulence in the presence of directional wind shear over the Rocky Mountains in Colorado is investigated. Directional-shear-induced critical levels are studied by taking 2D power spectra of the magnitude of the horizontal velocity perturbation field. In these spectra, a rotation of the most energetic wave modes with the background wind can be found. Such behaviour is consistent with the mechanism leading to wave breaking in directional shear flows.