Tracer interrelationships in the stratosphere

Relationships between long‐lived stratospheric tracers, manifested in similar spatial structures on scales ranging from a few to several thousand kilometers, are displayed most strikingly if the mixing ratio of one is plotted against another, when the data collapse onto remarkably compact curves. Distinct curves form in the polar vortex, the midlatitude “surf zones”, and the tropics. Theory predicts such relationships for sufficiently rapid mixing along isentropic surfaces. Model results are used to illustrate the formation and seasonal evolution of distinct tracer relationships in the different regions. Using such relationships to associate departures from canonical forms with anomalous chemical or microphysical behavior must be done with care and with full awareness of the meteorological context of the data. Although the theory has been developed in the context of stratospheric tracers, the key requirement is that transport is predominantly two‐dimensional. While the theory is thus inappropriate in the troposphere, it should be applicable to transport in the ocean interior.