The Lyapunov Diffusivity: a new diagnostic to detect local mixing events in the UTLS
Abstract
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 Nakamura's tracer-based effective diffusivity with the particle-based Lyapunov exponent. Application to consider isentropic mixing on the 350K surface shows there to be significant longitudinal variation to the strength of the barrier at the Northern subtropical jet, with the strongest barrier over Asia and the Western Pacific, a weaker barrier over the Western Atlantic, and mixing regions at the jet exits over the Eastern Pacific and Atlantic. The diagnostic highlights the seasonal cycle of the longitudinally varying mixing properties, in particular those associated with the monsoon circulations and with the westerly ducts in the subtropics. The mixing structure is shown to be modulated by modes of atmospheric variability. ENSO is shown to influence mixing in the equatorial Pacific and in the subtropics of the Pacific and Atlantic in association with changes to the westerly ducts. In the Eastern Atlantic and Mediterrenean, mixing is observed to be enhanced during the positive phase of the NAO. Variations associated with the QBO are also highlighted.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A24C..08S
- Keywords:
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- 0341 Middle atmosphere: constituent transport and chemistry (3334);
- 3334 Middle atmosphere dynamics (0341;
- 0342);
- 3362 Stratosphere/troposphere interactions