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1 JANUARY 1998 19A F A N A S Y E V A N D P E L T I E R 1998 American Meteorological Society

Summary: 1 JANUARY 1998 19A F A N A S Y E V A N D P E L T I E R
1998 American Meteorological Society
The Three-Dimensionalization of Stratified Flow over Two-Dimensional Topography
Department of Physics, University of Toronto, Toronto, Ontario, Canada
(Manuscript received 22 November 1996, in final form 15 April 1997)
The authors present a series of new analyses of the problem of stratified flow over a localized two-dimensional
obstacle, focusing upon the detailed dynamical characteristics of the flows that develop when the Froude number
is such that the forced internal waves ``break'' above their topographic source. Results demonstrate that when
the flow is restricted to evolve in two space dimensions, then the intensity of the Kelvin­Helmholtz-like (K­
H) perturbations that form in the downstream shear layer that separates the accelerated low-level jet in the lee
of the obstacle and the overlying region of decelerated flow increases dramatically with the governing parameter
NU/g (U and N are, respectively, the velocity and buoyancy frequency characteristic of the upstream incident
flow, while g is the gravitational acceleration). This nondimensional parameter represents the ratio of the ac-
celeration that a fluid particle feels in the wave to the gravitational acceleration and measures the importance
of non-Boussinesq effects. A marked change in the global characteristics of the flow is shown to occur with
increasing NU/g, characteristics that include the speed of downstream propagation of the so-called chinook front,
the drag exerted by the flow on the obstacle, and the intensity of the K­H instability induced pulsations of the
surface velocity field. When the flow is allowed to access the third spatial dimension, the authors demonstrate


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


Collections: Geosciences