Non-linear interaction of gravity waves with average jet flows, instabilities, and turbulence

This study describes several mechanisms, including the action of planetary waves, involved in the exchange of air between the troposphere and stratosphere. The first section looks at the problem of non-linear interaction between gravity waves and an average flow. The process sometimes produces instabilities that cause differential transport. When preconditions for the appearance of Kelvin-Helmholtz instabilities are altered slightly, instabilities can travel vertically, and through the tropopause. The second section looks at relief waves, and shows that gusts of wind can generate unsteady waves that can travel to the stratosphere and beyond. The final chapter considers jets. The interaction between the two critical levels found in jets accounts for their very different reflection and transmission of waves. When jet characteristics combine with instabilities, pseudo-instabilities-that is instabilities in places where the medium is stable are created.