Impact of stratospheric intrusions and intercontinental transport on ozone at Jungfraujoch in 2005: comparison and validation of two Lagrangian approaches 1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
2Laboratory for Air Pollution and Environmental Technology, EMPA, Dübendorf, Switzerland
Received: 05 Nov 2008 – Published in Atmos. Chem. Phys. Discuss.: 15 Jan 2009 – Published: 26 May 2009Abstract. The particle dispersion model FLEXPART and the trajectory model LAGRANTO are
Lagrangian models which are widely used to study synoptic-scale atmospheric
air flows such as stratospheric intrusions (SI) and intercontinental
transport (ICT). In this study, we focus on SI and ICT events particularly
from the North American planetary boundary layer for the Jungfraujoch (JFJ)
measurement site, Switzerland, in 2005. Two representative cases of SI and
ICT are identified based on measurements recorded at Jungfraujoch and are
compared with FLEXPART and LAGRANTO simulations, respectively. Both models
well capture the events, showing good temporal agreement between models and
measurements. In addition, we investigate the performance of FLEXPART and
LAGRANTO on representing SI and ICT events over the entire year 2005 in a
statistical 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 planetary
boundary layer during 13% (FLEXPART) and 12% (LAGRANTO) of the entire year.
Through intercomparsion with measurements, our findings suggest that both
FLEXPART and LAGRANTO are well capable of representing SI and ICT events if
they last for more than 12 h, whereas both have problems on representing
short events. For comparison with in-situ observations we used O3 and
relative humidity for SI events. As parameters to trace ICT events we used a
combination of NOy/CO and CO, however these parameters are not
specific enough to distinguish aged air masses by their source regions.
Moreover, a sensitivity study indicates that the agreement between models and
measurements depends significantly on the threshold values applied to the
individual control parameters. Generally, the less strict the thresholds are,
the better the agreement between models and measurements. Although the
dependence of the agreement on the threshold values is appreciable, it
nevertheless confirms the conclusion that both FLEXPART and LAGRANTO are well
able to capture SI and ICT events with duration longer than 12 h.
Citation: Cui, J., Sprenger, M., Staehelin, J., Siegrist, A., Kunz, M., Henne, S., and Steinbacher, M.: Impact of stratospheric intrusions and intercontinental transport on ozone at Jungfraujoch in 2005: comparison and validation of two Lagrangian approaches, Atmos. Chem. Phys., 9, 3371-3383, doi:10.5194/acp-9-3371-2009, 2009.