Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 4 3 2004 10.5194/acpd-4-3249-2004 http://www.atmos-chem-phys-discuss.net/4/3249/2004/ http://www.atmos-chem-phys-discuss.net/4/3249/2004/acpd-4-3249-2004.html http://www.atmos-chem-phys-discuss.net/4/3249/2004/acpd-4-3249-2004.pdf 3249 3284 2004-06-18 Stratosphere-troposphere exchange from the Lagrangian perspective: a case study and method sensitivities M. S. Bourqui bourqui@env.ethz.ch Institute for Atmospheric and Climate Science, ETHZ, Switzerland An important part of extra-tropical stratosphere-to-troposphere transport occurs in association with baroclinic wave breaking and cut-off decay at the tropopause. In the last decade many studies have attempted to estimate stratosphere-troposphere exchange (STE) in such synoptic events with various methods, and more recently efforts have been put on inter-comparing these methods. However, large uncertainties remain on the sensitivities to methods intrinsic parameters, and on the best measure for STE with regard to end effects on chemistry. <br><br> The goal of the present study is to address these two fundamental issues in the context of the application of a trajectory-based Lagrangian method, which has been applied in the past to climatological studies and has also been involved in inter-comparison studies, to a typical baroclinic wave breaking event. <br><br> The analysis sheds light on (i) the fine mesoscale temporal and spatial structures that are associated with episodic, rapid inflows of stratospheric air into the troposphere; (ii) the spatial resolution of 1&deg;&times;1&deg; required to reasonably capture STE fluxes in such a wave breaking event; (iii) the effective removal of spurious exchange events using a threshold residence time; (iv) the relevance of residence time distributions for capturing the effective chemical forcing of STE; (v) the large differences in the temporal evolution and geographical distribution of STE fluxes across the 2 and the 4 potential vorticity unit iso-surface definitions of the tropopause.