Royal Netherlands Meteorological Institute
Section of Atmospheric Composition
The propagation of inertia-gravity waves (IGWs) through a dynamical transport barrier, such as the Antarctic polar vortex edge has been investigated using a linear wave model. The model is based on the linearized, inviscid hydrostatic equations on an f-plane. Typical values for the parameters that are appropriate to the Antarctic polar vortex are assumed. The background flow is assumed to be barotropic and its horizontal shear is represented by a hyperbolic tangent background wind profile. The wave equation that describes the latitudinal structure of a monochromatic disturbance contains two singularities. The first corresponds to the occurrence of a critical level where the intrinsic wave frequency becomes zero. The second is an apparent singularity and does not give rise to singular wave behaviour. The wave equation is solved numerically for different values of the angles of incidence of the wave upon the background flow, and for different values of the wave frequency, the horizontal wavenumber and the Rossby number. Reflection and transmission coefficients are determined as a function of these parameters. The results depend on whether the flow is inertially stable or not. They also depend on the presence and location of the turning levels, where the wave becomes evanescent, with respect to the location of the critical levels. For inertially stable flows, the wave totally reflects at the turning level and never reaches the critical level. If the background flow is inertially unstable, turning levels can disappear and the wave can now reach the critical level. Then overreflection, overtransmission and absorption can occur.
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