Journal of Conference Abstracts

Mixing and Stratospheric Ozone Chemistry

Peter Haynes (phh@damtp.cam.ac.uk)

DAMTP, Silver Street, Cambridge, CB3 9EW, England

Recent work in which the sensitivity of stratospheric chemical evolution to mixing (and model representation of mixing) will be reported. This work motivates the more general question of understanding chemical evolution in chaotic advection flow (how the amount of different chemical species at any time depends on flow structure, initial conditions, molecular diffusivity, etc). (The stirring effects of the stratospheric flow seem to be dominated by large-scales and chaotic advection is therefore a useful therefore a relevant paradigm).

A theory will be presented for predicting chemical evolution of chaotic advection flows. The theory is based on considering the system as made up of a large number of elements, each of which experiences a different stretching history. For each element the chemical evolution is predicted by considering a canonical model problem, which is just the chemical evolution in the absence of stretching, except that the time is not real time, but an effective time that depends on the stretching history. The chemical state of the whole system at any real time is predicted by averaging over a large number of realisations of the canonical problem, each evaluated at a different effective time. The distribution of effective times is consistent with the distribution of stretching histories in the flow.

Predictions from the theory are compared to explicit simulations of a range of different flows, from simple shear flows to chaotic advection flows, and theory and simulation show good agreement.