Canonical Trace Gas Relationships and Altitude Spectrum of Air in the Arctic Vortex

In situ measurements of a suite of trace gases with stratospheric lifetimes from 5 to 120 years at 19-22 km in the Arctic vortex in 2000 suggest that canonical tracer relationships in the vortex are significantly different from those in middle latitudes. We demonstrate that these relationships, which are established as early as October-November and are diagnostic of the transport of the air and fate of ozone-depleting compounds, can form without significant entrainment of midlatitude air into the vortex. Because the timescales of mixing in the vortex are short compared to lifetimes of even the shortest lived trace gases, the photolysis is not important in forming canonical vortex relationships. What is important is the altitude that air parcels descend from to form a given parcel in the vortex by mixing with other parcels from other altitudes. To obtain a distribution of the original altitudes in air parcels in the vortex we analyze a simple integral model of the evolution of the midlatitude canonical tracer relationship to the vortex ones. This model shows that in the mature arctic vortex the air at the 20 km altitude consists of about 70% of the air originated at higher altitudes and 10% from the lower altitudes. This air mixes quasi-horizontally inside the vortex to form a canonical vortex relationship. These results also conform to existing transport models that indicate that the entire mesosphere may be flushed and descended into a winter polar vortex.