Transport and mixing processes across the arctic polar vortex edge may influence the climate relevant ozone layer both inside the vortex and at mid-latitudes. In-mixing of mid- latitude air into the vortex may have impact on the chemistry and the resulting polar ozone loss. Mixing of depleted vortex air masses into the mid-latitudes may reduce the ozone layer at mid-latitudes. The knowledge of transport and mixing processes is thus important for reliable predictions of the future evolution of the ozone layer.
In this thesis I present an index (vortex index) derived from in-situ N₂O measurements. This vortex index provides information on the characteristic origin of an air mass and enables transport analyses independent of the absolute values of trace gas mixing ratios. Moreover, the vortex index is a good proxy for the fraction of vortex air in an observed air mass.
Mixing between air masses of different origin is evaluated by an analysis of the F11-N₂O correlation. The vortex index allows mixed and unmixed air masses to be distinguished in this analysis.
The trace gases CFC-11 and N2O, along with CFC-12, H-1211, CH₄, SF₆, H₂and CO₂, were measured by the High Altitude Gas Analyzer (HAGAR) during the RECONCILE aircraft campaign (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) between mid January and mid March 2010.
The winter 2009/2010 was dynamically very active. This allows different processes like intrusions of mid-latitude air into the vortex and an extrusion of vortex air into the mid- latitudes to be investigated. The transport barrier between the surf zone and the vortex is identified as a region of weak and small-scale mixing. A further transport and mixing event outside the vortex was associated with a tropical streamer transported and mixed into high latitudes.
These single events were also evaluated by simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS). The results of the simulations were compared with the observations. Single transport events are represented well in the model. However, mixing between transported air masses and surrounding air appears to be stronger in the simulations than observed. This may be due to the limited horizontal resolution of the model. The simulated meridional transport as a whole was assessed using the calculated vortex index, which allows the validation of the isentropic model transport independent of model initialisation and the vertical transport in the model.
The chemical ozone loss between mid January and mid March was derived from the evolution of the observed O₃-N₂O correlation. The vortex index facilitates this analysis by identifying unmixed air masses. Taking into account mixing and transport is essential to avoid an underestimation of ozone loss. In this case the omission of mixing leads to an underestimation of about 35%. The maximal value of 1.4±0.5ppm ozone loss was derived for mid March at a potential temperature of 490K. The CLaMS model tends to an underestimation of ozone loss, but its results agree with the observations within the error bars.