Consideration of Lifetimes of Tracers for the Determination of Stratospheric Age Spectra and the Brewer Dobson Circulation (CoLiBri)

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The goal of this project is to explore the use of long-lived trace species to constrain stratospheric circulation under consideration of tracer lifetimes. From Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements global distributions of SF6, CFC-11, CFC-12, HCFC-22, CH4, N2O and H2O are available. The inference of age of stratospheric air from SF6 distributions is straight forward since there are no stratospheric sinks, and has already been performed to assess the intensity of the Brewer Dobson circulation. The use of the other tracers for this purpose is more challenging, since their specific lifetimes have to be considered. Since the decomposition of these species is altitude and latitude-dependent, their effective lifetimes depend in turn on the velocity of the Brewer Dobson circulation. This project shall tackle this problem in the following steps: (a) An altitude- and latitude-dependent parametrization of tracer lifetimes will be developed, in order to make these gases usable as age-tracers; (b) from latitude- and altitude dependent age of air distributions derived from MIPAS SF6 measurements, circulation and mixing patterns will be inferred; (c) on the basis of these circulation and mixing patterns and local lifetime estimates, tracer distributions will be deduced and compared to the tracer distributions measured by MIPAS; (d) discrepancies between calculated and measured tracer distributions will be analyzed to identify inappropriate assumptions on mixing and transport processes.