Large-scale mixing in the middle atmosphere

                        Keith Ngan 
        Atmospheric & Oceanic Sciences, McGill University

The mixing of passive scalars in the middle atmosphere has received
much attention in recent years. In this work we describe the
application of ideas from dynamical systems theory and discuss the
connections with turbulence phenomenology. Using data obtained from
numerical models of the middle atmosphere, we demonstrate that while
chaotic advection occurs in the lower stratosphere and upper
troposphere, the situation in the upper stratosphere is more complex
and analogous to that in prototypically complex, spectrally local
flows. Although we focus upon the geometry and statistics of
large-scale mixing in the absence of diffusion, we also describe some
work on the equilibrium statistics of a randomly advected and diffused
passive scalar, and its potential implications for analyses of
chemical data.