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The particle dispersion model FLEXPART and the trajectory model LAGRANTO areLagrangian models which are widely used to study synoptic-scale atmosphericair flows such as stratospheric intrusions (SI) and intercontinentaltransport (ICT). In this study, we focus on SI and ICT events particularlyfrom the North American planetary boundary layer for the Jungfraujoch (JFJ)measurement site, Switzerland, in 2005. Two representative cases of SI andICT are identified based on measurements recorded at Jungfraujoch and arecompared with FLEXPART and LAGRANTO simulations, respectively. Both modelswell capture the events, showing good temporal agreement between models andmeasurements. In addition, we investigate the performance of FLEXPART andLAGRANTO on representing SI and ICT events over the entire year 2005 in astatistical way. We found that the air at JFJ is influenced by SI during 19%(FLEXPART) and 18% (LAGRANTO), and by ICT from the North American planetaryboundary layer during 13% (FLEXPART) and 12% (LAGRANTO) of the entire year.Through intercomparsion with measurements, our findings suggest that bothFLEXPART and LAGRANTO are well capable of representing SI and ICT events ifthey last for more than 12 h, whereas both have problems on representingshort events. For comparison with in-situ observations we used O<sub>3</sub> andrelative humidity for SI events. As parameters to trace ICT events we used acombination of NO<sub>y</sub>/CO and CO, however these parameters are notspecific enough to distinguish aged air masses by their source regions.Moreover, a sensitivity study indicates that the agreement between models andmeasurements depends significantly on the threshold values applied to theindividual control parameters. Generally, the less strict the thresholds are,the better the agreement between models and measurements. Although thedependence of the agreement on the threshold values is appreciable, itnevertheless confirms the conclusion that both FLEXPART and LAGRANTO are wellable to capture SI and ICT events with duration longer than 12 h

atmospheric chemistry and physics

Impact of stratospheric intrusions and intercontinental transport on ozone at Jungfraujoch in 2005: comparison and validation of two Lagrangian approaches