Stratospheric dynamics: Age-of-air

[johannespletzer]

Background
I recently tested ESMValTools autoassess/stratosphere/age_of_air.py script with the intention to calculate age-of-air (issue #4417). I found it rather limited and deprecated. @schlunma mentioned that colleagues from the MetOffice created the original script. I would like to discuss if a script to calculate age-of-air would be a valuable addition to the ESMValTool?

Motivation
I am working on the topic, since age-of-air allows to estimate stratospheric residence time of emitted trace gases. This is relevant in the context of volcanic eruptions, aircraft and rocket emissions and re-entries of satellites. These topics are increasingly focused on in research. I could provide an existing and validated script targeted at a linearly increasing SF6 (AOA) tracer in the EMAC model (not suited for observations that show non-linear behavior). I would need help to generalize that to model data used by the ESMValTool.