Various particle- and tracer-based diganositics are used to investigate the mixing and transport in the upper troposphere and lower stratosphere, including effective diffusivity and finite-time / finite-size Lyapunov exponents. Although all three diagnostics indicate the presence of mixing regions and barriers at approximately the same locations, there are important differences between them. These differences between the diagnostics are used to gain a fuller understanding of the mixing process.

Calculations of effective diffusivity indicate that the mixing in the upper troposphere is significantly modified by ENSO, particularly in the Northern Hemisphere. In the winter hemisphere the barrier associated with the subtropical jet is strengthened in El Nino years, whereas in the summer hemisphere the mixing associated with the Asian monsoon circulation is significantly strengthened in La Nina years. Similar results are obtained from contour stretching calculations. Possible mechanisms for driving the observed influence are discussed.