Observations of planetary waves in the Southern Hemisphere stratosphere suggest that the waves evolve in episodes of growth and decay over a few weeks. Within such an episode, the waves occasionaly show variations in the vertical phase structure on the time scales of a few days. We view the waves as evolving towards a steady state modal structure in a wave guide that follows the polar night jet, and is leaky on the equatorial side. The waves propagate along the wave guide, and leak through the side towards the equator because of the existence of a critical surface there.
A quasi-geostrophic, linear, time dependent model is used to study the propagation into the stratosphere of a perturbation forced at the tropopause. A technique that follows a wave packet on its journey through the stratosphere, while keeping track of variations in wave activity that are due to refraction of the waves, is introduced and applied to the model runs. This allows us, among other things, to get a time scale for vertical propagation through the stratosphere. A perturbation that is forced at the tropopause initially concentrates into the center of the wave guide as it propagates. After some time it leaks trough the equatorial boundary and tunnels through to the critical surface.
The consequences of a leaky waveguide configuration for the evolution of perturbations that are forced at the bottom of the domain will be discussed briefly.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics