Local mixing events in the upper-troposphere and lower-stratosphere. Part I: detection with the Lyapunov diffusivity

A new diagnostic (the "Lyapunov diffusivity'') is presented that has the ability to quantify isentropic mixing in diffusion units and detects local mixing events by describing latitude-longitude variability. It is a hybrid diagnostic, combining the tracer-based effective diffusivity with the particle-based Lyapunov exponent calculation. Isentropic mixing on the 350-K surface shows that there is significant longitudinal variation to the strength of mixing at the northern subtropical jet, with a strong mixing barrier over Asia and the western Pacific, a weaker mixing barrier over the western Atlantic, and active mixing regions at the jet exits over the eastern Pacific and Atlantic.