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132 VOLUME 58J O U R N A L O F T H E A T M O S P H E R I C S C I E N C E S 2001 American Meteorological Society

Summary: 132 VOLUME 58J O U R N A L O F T H E A T M O S P H E R I C S C I E N C E S
2001 American Meteorological Society
Numerical Simulations of Internal Gravity Wave Breaking in the Middle Atmosphere:
The Influence of Dispersion and Three-Dimensionalization
Department of Physics, University of Toronto, Toronto, Ontario, Canada
(Manuscript received 19 April 1999, in final form 9 February 2000)
A series of new analyses of the problem of the evolution of the internal gravity wave field that is excited
when a uniformly stratified fluid flows over monochromatic topography is presented. Results demonstrate that
upward-propagating waves overturn and break when they reach sufficient amplitude. The breaking of the wave
field may occur due to either one or the other of two main effects, namely, the instability of the propagating
wave front and the instability of the wave established behind the advancing front. The analysis of the wave­
mean flow momentum transfer process reveals significant differences between these results and the predictions
of two main gravity wave drag parameterization schemes (viz., those based upon so-called saturation theory
and the spectral theory based on the critical layer absorption mechanism) regarding the dynamics of wave
breaking and the spatial distribution of the resulting momentum transfer. The vertical extent and structure of
the breaking region and, hence, the momentum transfer from the wave field to the mean flow, are shown to be
highly sensitive to the governing parameter aN/U (U and N are, respectively, the velocity and buoyancy frequency
characteristic of the upstream incident flow, while a is the wavelength of a quasi-topographic forcing). This


Source: Afanassiev, Iakov - Department of Physics and Physical Oceanography, Memorial University of Newfoundland


Collections: Geosciences