Comparison of cross-tropopause transport and ozone in the upper troposphere and lower stratosphere region

Wintertime tracer transport in the atmospheric "middle world" is analysed for five winters using three different advection methods, namely Eulerian advection, reverse domain-filling trajectory calculations, and contour advection with a diagnosis of filaments. In all approaches, isentropic motion is assumed. The results are compared to synopses of ozone derived from the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) airborne ozone measurement program. Tracer and ozone data are cast into the "reduced" space spanned by equivalent latitude, potential temperature, and time. In this representation some anomalies of MOZAIC ozone are mirrored in corresponding features of stratospheric tracer mass mixing ratios. Eulerian and reverse domain-filling trajectory studies give similar results, suggesting that numerical diffusion only plays a minor role. Tracer transport out of the stratosphere minimizes in the height range of 340 to 350 K, The trajectory studies reveal preferred regions of isentropic stratosphere-troposphere exchange associated with the positions of storm tracks. These asymmetries are similar to asymmetries in the correlation of potential vorticity (PV) and ozone found in the MOZAIC data. Zonal asymmetries are also found in the occurrence of filamentary structure in the contour advection simulations with filamentation maximizing downstream of the North Atlantic storm track. Hemispheric- and seasonal-mean filamentation activity is strongly correlated with stratosphere-troposphere exchange discerned from the Lagrangian transport experiments. In both signals the winter of 1997/1998 shows the lowest activity of the five winters analyzed here. A drop in activity in the winter of 1995/1996 may, however, be related to the introduction of a more advanced data assimilation scheme to the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis cycle. This change may also be partly responsible for a somewhat improved correlation of PV and MOZAIC ozone at high equivalent latitudes after the winter of 1994/1995.