Q. J. Roy. Met. Soc. (2005), 131, 247-258.
It is argued that certain aspects of tracer patterns and related stirring by the flow in the extratropical tropopause region can be understood in terms of a transition between dynamically active and passive tracer advection, called "active to passive tracer transition". In the framework of surface quasi-geostrophic dynamics a specific initial value problem is defined and investigated. It features a gradual transition between the two paradigms of tracer advection and allows a clear interpretation thanks to the idealized nature of the model set-up. Physical reasoning and anecdotal evidence from previous studies suggests that, at least in specific cases, this interpretation is relevant for the real atmosphere.