Mountain wave breaking in atmospheric flows with directional wind shear

Flow over mountains generates internal gravity waves in the atmosphere, generally known as mountain waves. High-amplitude, near breaking, mountain waves are associated with downslope windstorms (which are important for local weather) and clear-air turbulence generation aloft (which is important for aviation safety). These waves may produce a drag force that exceeds small-amplitude estimates by an order of magnitude, giving a very large contribution to the deceleration of the global atmospheric circulation (which is important for drag parametrization in global climate and weather prediction models, that do not resolve this force). In the real atmosphere, mountain wave breaking may be triggered by 2 dimensional critical levels, where the wind velocity vanishes, but whether 3 dimensional critical levels, associated with turning of the wind with height in flows with directional shear, cause wave breaking, and how this happens, is still largely unknown. Since breaking waves are highly nonlinear, only numerical simulations will ultimately be able to clarify this issue. In this project, numerical simulations will be carried out to address the problem of mountain wave breaking in flows with directional shear, and its implications for downslope windstorms, clear-air turbulence and drag parametrization. Quantitative criteria for the occurrence of breaking will be investigated, initially using idealized wind profiles and orography, and later progressing to more realistic conditions.

Further details of the project can be found at
http://www.met.reading.ac.uk/pg-research/teixeira_proj1.pdf

General information on the PhD programme at the Department of Meteorology can be found at
http://www.met.reading.ac.uk/pg-research/