ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-15559-2010 Transport analysis of ozone enhancement in Southern Ontario during BAQS-Met He H. 1 Tarasick D. W. 1 Hocking W. K. 2 Carey-Smith T. K. 3 Rochon Y. 1 Zhang J. 1 Makar P. A. 1 Osman M. 2 Brook J. 1 Moran M. 1 Jones D. 4 Mihele C. 1 Wei J. C. 5 Osterman G. 6 Argall P. S. 2 McConnell J. 7 Bourqui M. S. 8 Air Quality Research Division, Science and Technology Branch, Environment Canada, Downsview, ON, Canada Department of Physics and Astronomy, University of Western Ontario, London, ON, Canada National Institute of Water and Atmospheric Research Ltd., Private Bag 14901, Kilbirnie, Wellington, New Zealand Department of Physics, University of Toronto, Toronto, ON, Canada Perot Systems Government Services, NOAA/NESDIS/STAR, USA Jet Propulsion Laboratory, NASA, USA Department of Earth and Space Science and Engineering, York University, Toronto, ON, Canada Department of Chemistry and Atmospheric and Oceanic Sciences, McGill University, Montreal, QC, Canada 24 06 2010 10 6 15559 15593 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/10/15559/2010/acpd-10-15559-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/15559/2010/acpd-10-15559-2010.pdf

Twice-daily ozonesondes were launched from Harrow, Ontario (east of Detroit) during the BAQS-Met (Border Air Quality and Meteorology Study) campaign in the summer of 2007. A co-located radar windprofiler measured tropopause height continuously. Simulation results from the dispersion model FLEXPART, using the output of the Environment Canada Global Environmental Multiscale (GEM) weather forecast model, indicate the occurrence of stratospheric ozone intrusion events during the BAQS-Met campaign. This interpretation is supported by the ozonesonde observations, one-minute average surface ozone data measured by the chemistry supersite at Harrow, and geostatistical interpolation results of satellite ozone data that were observed from TES (Tropospheric Emission Spectrometer) onboard NASA's Aura satellite and AIRS (Atmospheric Infrared Sounder) onboard NASA's Aqua satellite. Source-receptor analysis using the GEM-FLEXPART model shows the stratosphere over the Northwest Territories region close to the Beaufort Sea to be the main source of the enhanced ozone at Harrow on 1 July 2007.

 References Ancellet,~G., Beekmann,~M., and Papayannis,~A.: Impact of a~cutoff low development on downward transport of ozone in the troposphere, J. Geophys. Res., 99, 3451–3468, 1994. Appenzeller,~C., Holton,~J R., and Rosenlof,~K H.: Seasonal variation of mass transport across the tropopause, J. Geophys. Res., 101(D10), 15071–15078, doi:10.1029/96JD00821, 1996. Bayraktar~H. and Turalioglu,~F S.: A~Kriging-based approach for locating a~sampling site – in the assessment of air quality, Stoch. Environ. Res. Risk Assess. (SERRA), 19(4), doi:10.1007/s00477-005-0234-8, 301–305, 2005. Beekmann, M., Ancellet, G., Blonsky, S., et al.: Regional and global tropopause fold occurence and related ozone flux across the tropopause, J. Atmos. Chem., 28, 29–44, 1997. Beer,~R., Glavich,~T A., and Rider,~D M.: Tropospheric emission spectrometer for the earth observing system aura satellite, Appl. Opt., 40, 2356–2367, 2001. Beer,~R.: TES on the aura mission: scientific objectives, measurements, and analysis overview, IEEE Trans. Geosci. Remote Sens., 44, 1102– 1105, 2006. Bian,~J., Gettelman,~A., Chen,~H., and Pan,~L L.: Validation of satellite ozone profile retrievals using Beijing ozonesonde data, J. Geophys. Res., 112, D06305, doi:10.1029/2006JD007502, 2007. Bonasoni,~P., Evangelisti,~F., Bonafe',~U., Feldmann,~H., Memmesheimer,~M., Stohl,~A., Tositti,~L., Kromp-Kolb,~H., and Colombo,~T.: Stratosphere-troposphere exchanges: case studies recorded at Mt. Cimone during the VOTALP project, Phys. Chem. Earth, 24C, 443–446, 1999. Bonasoni,~P., Evangelisti,~F., Bonafe',~U., Ravegnani,~F., Calzolari,~F., Stohl,~A., Tositti,~L., Tubertini,~O., and Colombo,~T.: Stratospheric ozone intrusion episodes recorded at Mt. Cimone during the VOTALP project: case studies, Atmos. Environ., 34, 1355–1365, 2000. Bourqui,~M S. and Trepanier,~P Y.: Descent of deep stratospheric intrusions during the IONS august 2006 campaign, J. Geophys. Res., in press., 2010. Boxe, C. S., Worden, J. R., Bowman, K. W., Kulawik, S. S., Neu, J. L., Ford, W. C., Osterman, G. B., Herman, R. L., Eldering, A., Tarasick, D. W., Thompson, A. M., Doughty, D. C., Hoffmann, M. R., and Oltmans, S. J.: Validation of northern latitude tropospheric emission spectrometer stare ozone profiles with ARC-IONS sondes during ARCTAS, Atmos. Chem. Phys. Discuss., 9, 27267–27301, doi:10.5194/acpd-9-27267-2009, 2009. Carey-Smith~T K., Tarasick,~D W., Hocking,~W K., Cooper,~O R., He,~H., Liu,~G., Argall,~P S., and Rochon,~Y.: High resolution measurements of stratosphere-troposphere exchange using radar windprofilers and ballon-borne ozonesondes, submitted to Atmos. Chem. Phys., 2010. Cooper,~O R., Moody,~J L., Daveport,~J C., Oltmans,~S J., Johnson,~B J., Chen,~X., Shepson,~P B., and Merrill,~J T.: Influence of springtime weather systems on vertical ozone distributions over three North American sites, J. Geophys. Res., 103, 22001–22013, 1998. Cooper,~O R., Forster,~C., Parrish,~D., Dunlea,~E., Habler,~G., Fehsenfeld,~F., Holloway,~J., Oltmans,~S., Johnson,~B., Wimmers,~A., and Horowitz,~L.: On the life-cycle of a~stratospheric intrusion and its dispersion into polluted warm conveyor belts, J. Geophys. Res., 109, 2004, doi:10.1029/2003JD004006, 2004. Cooper, O. R., Stohl, A., Hübler, G., et al.: Direct transport of midlatitude stratospheric ozone into the lower troposphere and marine boundary layer of the tropical Pacific Ocean, J. Geophys. Res., 110, D23310, doi:10.1029/2005JD005783,~2005. Cooper,~O R., Stohl,~A., Trainer,~M., Thompson,~A., Witte,~J C., Oltmans,~S J., Johnson,~B J., Merrill,~J., Moody,~J L., Morris,~G., Tarasick,~D., Forbes,~G., Nédélec,~P., Fehsenfeld,~F C., Meagher,~J., Newchurch,~M J., Schmidlin,~F J., Turquety,~S., Crawford,~J H., Pickering,~K E., Cohen,~R C., Bertram,~T., Wooldridge,~P., and Brune,~W H.: Large upper tropospheric ozone enhancements above mid-latitude North America during summer: in situ evidence from the IONS and MOZAIC ozone monitoring network, J. Geophys. Res., D24S05, doi:10.1029/2006JD007306, 2006. Côté,~J., Gravel,~S., Methot,~A., Patoine,~A., and Roch,~M., The operational CMC-MRB Global Environmental Multiscale (GEM) model, part I: Design considerations and formulation, Mon. Weather Rev., 126(6), 1373–1395, 1998. Cristofanelli,~P., Bonasoni,~P., Collins,~W., Feichter,~J., Forster,~C., James,~P., Kentarchos,~A., Kubik,~P W., Land,~C., Meloen,~J., Roelofs,~G J., Siegmund,~P., Sprenger,~M., Schnabel,~C., Stohl,~A., Tobler,~L., Tositti,~L., Trickl,~T., and Zanis,~P.: Stratosphere-to-troposphere transport: a~model and method evaluation, STACCATO special section of J. Geophys. Res., 108, 8525, doi:10.1029/2002JD002600, 2003. Davies,~T D. and Schuepbach,~E.: Episodes of high ozone concentrations at the earth's surface resulting from transport down from the upper troposphere/lower stratosphere: a~review and case studies, Atmos. Environ., 28(1), 53–68, 1994. Elbern,~H., Hendricks,~J., and Ebel,~A.: A~climatology of tropopause folds by global analyses, Theor. Appl. Climatol., 59(3–4), 181–200, 1998. Emanuel,~K A. and Zivkovie-Rothman,~M.: Development and evaluation of a~convection scheme for use in climate models, J. Atmos. Sci., 56, 1766–1782, 1999. Emery,~X.: Simple and ordinary Kriging multigaussian Kriging for estimating recovevearble reserves, Math. Geol., 37(3), 295–319, 2005. Fetzer,~E J., Lambrigtsen,~B H., Eldering,~A., Aumann,~H H., and Chahine,~M T.: Biases in total precipitable water vapor climatologies from atmospheric infrared sounder and advanced microwave scanning radiometer, J. Geophys. Res., 111, D09S16, doi:10.1029/2005JD006598, 2006. Fischer,~H., Wienhold,~F G., Hoor,~P., Bujok,~O., Schiller,~C., Siegmund,~P., Ambaum,~M., Scheeren,~H A., and Lelieveld,~J.: Tracer correlations in the northern high latitude lowermost stratosphere: influence of cross-tropopause mass exchange, Geophys. Res. Lett., 27, 97–100, 2000. Forster, C., Cooper O., Stohl, A., et al.: Lagrangian transport model forecasts and a~transport climatologyfor the Intercontinental Transport and Chemical Transformation 2002 (ITCT2K2) measurement campaign, J. Geophys. Res., 109, D07S92, doi:10.1029/2003JD003589,~2004. Gage,~K S., Ecklund,~W L., Riddle,~A C., and Balsley,~B B.: Objective tropopause height determination using low-resolution VHF radar observations, J. Atmos. Ocean. Tech., 3, 248–254, 1996. Gong,~W., Dastoor,~A P., Bouchet,~V S., Gong,~S., Makar,~P A., Moran,~M D., Pabla,~B., Ménard,~S., Crevier, L.-P., Cousineau,~S., and Venkatesh,~S.: Cloud processing of gases and aerosols in a~regional air quality model (AURAMS), Atmos. Res., 82, 248–275, 2006. Goovaerts, P.: Geostatistics for natural resource evaluation, 1997. Hocking,~W K.: System design, signal-processing procedures, and preliminary results for the Canadian (London, Ontario) VHF atmospheric radar, Rad. Sci., 32(2), 687–706, 1997. Hocking,~W K., Carey-Smith,~T K., Tarasick,~D W., Argall,~P S., Strong,~K., Rochon,~Y., Zawadzki,~I., and Taylor,~P A.: Detection of stratospheric ozone intrusion by windprofiler radars, Nature, 450(7167), 281–284, doi:10.1038/nature06312, 2007. Holton,~J R., Haynes,~P H., McIntyre,~M E., Douglas,~A R., Rood,~R B., and Pfister,~L.: Stratosphere-troposphere exchange, Rev. Geophys., 33, 403–439, 1995. Hooper,~D A. and Arvelius,~J.: Monitoring of the Arctic winter tropopause: a~comparison of radiosonde, ozondesonde and MST radar observations, in: Proc. MST9-COST76, edited by: Edwards,~B., SCOSTEP and Meteo France, 385–388, 2000. James,~P., Stohl,~A., Forster,~C., Eckhardt,~S., Seibert,~P., and Frank,~A.: A~15-year climatology of stratosphere-troposphere exchange with a~Lagrangian particle dispersion model: 2. mean climate and seasonal variability, STACCATO special section of J. Geophys. Res., 108, 8522, doi:10.1029/2002JD002639, 2003a. James,~P., Stohl,~A., Forster,~C., Eckhardt,~S., Seibert,~P., and Frank,~A.: A~15-year climatology of stratosphere-troposphere exchange with a~Lagrangian particle dispersion model: 1. methodology and validation, STACCATO special section of J. Geophys. Res., 108, 8519, doi:10.1029/2002JD002637, 2003b. Journel,~A G. and Huijbregts,~C J.: Mining Geostatistics, Academic Press, London, 1978. Kollonige,~D W., McMillan,~W., Osterman,~G., Browell,~E., and Irion,~B.: Observations of stratospheric intrusions from the A-Train in 2006 during INTEX-B, AIRS Meeting, 9–12 Oct 2007. Kulawik,~S S., Worden,~H., Osterman,~G., Luo,~M., Beer,~R., Kinnison,~D., Bowman,~K W., Worden,~J., Eldering,~A., Lampel,~M., Steck,~T., Rodgers,~C.: TES atmospheric profile retrieval characterization: an orbit of simulated observations, IEEE T. Geosci. Remote Sens., 44, 1324–1333, 2006. Liu,~G., Tarasick,~D W., Fioletov,~V E., Sioris,~C E., and Rochon,~Y J.: Ozone correlation lengths and measurement uncertainties from analysis of historical ozonesonde data in North America and Europe, J. Geophys. Res., 114, D04112, doi:10.1029/2008JD010576, 2009. Makar, P. A., Zhang, J., Gong, W., Stroud, C., Sills, D., Hayden, K. L., Brook, J., Levy, I., Mihele, C., Moran, M. D., Tarasick, D. W., and He, H.: Mass tracking for chemical analysis: the causes of ozone formation in southern Ontario during BAQS-Met 2007, Atmos. Chem. Phys. Discuss., 10, 14241–14312, doi:10.5194/acpd-10-14241-2010, 2010a. Makar, P. A., Gong, W., Mooney, C., Zhang, J., Davignon, D., Samaali, M., Moran, M. D., He, H., Tarasick, D. W., Sills, D., and Chen, J.: Dynamic Adjustment of Climatological Ozone Boundary Conditions for Air-Quality Forecasts, Atmos. Chem. Phys. Discuss., 10, 13643–13688, doi:10.5194/acpd-10-13643-2010, 2010b. Meloen,~J., Siegmund,~P., van Velthoven,~P., Kelder,~H., Sprenger,~M., Wernli,~H., Kentarchos,~A., Roelofs,~G., Feichter,~J., Land,~C., Forster,~C., James,~P., Stohl,~A., Collins,~W., and Cristofanelli,~P.: Stratosphere troposphere exchange: a~model and method intercomparison, STACCATO special section of J. Geophys. Res., 108, 8526, doi:10.1029/2002JD002274, 2003. McPeters,~R D., Labow,~G J., and Logan,~J A.: Ozone climatological profiles for satellite retrieve algorithms, J. Geophys. Res., 112, D05308, doi:10.1029/2005JD006823, 2007. Monahan,~K P., Pan,~L L., McDonald,~A., Bodeker,~G E., Wei,~J C., George,~S., Barnet,~C., and Maddy,~E S.: Validation of AIRS v4 ozone profiles in the UTLS using ozonesondes from Lauder, NZ and Bounder, USA, J. Geophys. Res., 112, D17304, doi:10.1029/2006JD008181, 2007. Nassar,~R., Logan,~J A., Worden,~H M., Megretskaia,~I A., Bowman,~K W., Osterman,~G B., Thompson,~A M., Tarasick,~D W., Austin,~S., Claude,~H., Dubey,~M K., Hocking,~W K., Johnson,~B J., Joseph,~E., Merrill,~J., Morris,~G., Newchurch,~M., et al.: Validation of Tropospheric Emission Spectrometer (TES) nadir ozone profiles using ozonesonde measurements, J. Geophys. Res., 113, D15S17, doi:10.1029/2007JD008819,~2008. Olsen, E. T., Fishbein, E., Hearty, T., et al.: AIRS version 5 release level 2 standard product quickstart, AIRS Data Document,~2007a. Olsen, E. T., Friedman, S., Fishbein, E., et al.: AIRS/AMSU/HSB version 5 changes from verstion 4, AIRS Data Document,~2007b. Oltmans,~S J., Raatz,~W E., and Komhyr,~W D.: On the transfer of stratospheric ozone into the troposphere near the North Pole, J. Atmos. Chem., 9, 245–253, 1989. Osterman,~G B.: TES level 2 algorithm theoretical basis document, Version 1.16, JPLD-16474, 2004. Pan,~L L.: STE studies using AIRS data, AIRS Meeting, 7–10 Mar 2006. Pan~L L., Randel,~B., Wei,~J C., and Irion,~B.: Use of the AIRS data in the research of UTLS chemistry and dynamics, AIRS Meeting, 9–12 Oct 2007a. Pan,~L L., Bowman,~K P., Shapiro,~M., Randel,~W J., Gao,~R S., Campos,~T., Davis,~C., Schauffler,~S., Ridley,~B A., Wei,~J C., and Barnet,~C.: Chemical behavior of the tropopause observed during the stratosphere-troposphere analyses of regional transport experiment, J. Geophys. Res., 112, D18110, doi:10.1029/2007JD008645, 2007b. Parrington,~M., Jones,~D B A., Bowman,~K W., Thompson,~A M., Tarasick,~D W., Merrill,~J., Oltmans,~S J., Leblanc,~T., Witte,~J C., and Millet,~D B.: The impact of the assimilation of ozone data from the Tropospheric Emission Spectrometer on surface ozone across North America, Geophys. Res. Lett., doi:10.1029/2008GL036935, 2009. Price,~J D. and Vaughan,~G.: On the potential for stratosphere-troposphere exchange in cutoff low system, Q. J. Roy. Meteor. Soc., I19, 343–365, 1993. Richmond,~A.: Financially efficient ore selection incorporating grade uncertainty, Math. Geol., 35(2), 195–215, 2003. Rodgers,~C.: Inverse methods for atmospheric sounding: theory and practise, World Sci., Hackensack, NJ, 2000. Sacks~J., Welch,~W J., Mitchell,~T., and Wynn,~H P.: Design and analysis of computer experiments, Stat. Sci., 4, 409–435, 1989. Schoeberl, M. R., Douglass, A. R., Hilsenrath, E., et al.: Overview of the EOS aura mission, IEEE Trans. Geosci. Remote Sens., 44(5), 1066–1074, 2006. Seibert,~P., Kruger,~B., and Frank,~A.: Parameterisation of convective mixing in a~Lagrangian particle dispersion model, paper presented at 5th GLOREAM Workshop, Paul Scherrer Inst., Wengen, Switzerland, 24–26 Sep 2001. Singh,~H B., Viezee,~W., Johnson,~W B., and Ludwig,~F L.: The impact of stratospheric ozone on tropospheric air quality, JAPCA J. Air Waste Ma., 30, 1009–1017, 1980. Sprenger,~M., Wernli,~H., and Bourqui,~M S.: Stratosphere-troposphere exchange and its relation to potential vorticity streamers and cutoffs near the extratropical tropopause, J. Atmos. Sci., 64(5), 1587–1602, 2007. Stein,~A., wan der Meer,~F., and Gorte,~B.: Spatial statistics for remote sensing, Kluwer Academic Publishers, Dordrecht, Netherland, 2002. Stevenson, D. S., Dentener, F. J., Schultz, M. G., et al.: Multimodel ensemble simulations of present-day and near future tropospheric ozone, J. Geophys. Res., 111, doi:10.1029/2005JD006338,~2006. Stohl,~A., Hittenberger,~M., and Wotawa,~G.: Validation of the Lagrangian particle dispersion model FLEXPART against large scale tracer experiment data. Atmos. Environ., 24, 4245–4264, 1998. Stohl,~A. and Thomson,~D J.: A~density correction for Lagrangian particle dispersion modles, Boud. Lay. Meteorol., 90, 155–167, 1999. Stohl,~A., Spichtinger-Rakowsky,~N., Bonasoni,~P., Feldmann,~H., Memmesheimer,~M., Scheel,~H E., Trickl,~T., Hübener,~S H., Ringer,~W., and Mandl,~M.: The influence of stratospheric intrusions on alpine ozone concentrations, Atmos. Environ., 34, 1323–1354, 2000. Stohl,~A.: Computation, accuracy and applications of trajectories – a~review and bibliography, in: Air Pollution Science for the 21st Century, edited by: Austin,~J., Brimblecombe,~P., and Sturges,~W., Elsevier Science Ltd., Amsterdam, The Netherlands, 615–654, 2002a. Stohl,~A.: Long-range transport and stratosphere/troposphere exchange: learning from satellite data, in: Proceedings from the EUROTRAC-2 Symposium 2002, edited by: Midgley,~P M. and Reuther,~M., Margraf Verlag, Weikersheim, Germany, 127–132, 2002b. Stohl, A., Eckhardt, S., Forster, C., et al.: A~replacement for simple back trajectory calculation in the interpretation of atmospheric trace substance measurements, Atmos. Environ., 36, 4635–4648, 2002. Stohl,~A., Bonasoni,~P., Cristofanelli,~P., Collins,~W., Feichter,~J., Frank,~A., Forster,~C., Gerasopoulos,~E., Gäggeler,~H., James,~P., Kentarchos,~T., Kreipl,~S., Kromp-Kolb,~H., Krüger,~B., Land,~C., Meloen,~J., Papayannis,~A., Priller,~A., Seibert,~P., Sprenger,~M., Roelofs,~G J., Scheel,~E., Schnabel,~C., Siegmund,~P., Tobler,~L., Trickl,~T., Wernli,~H., Wirth,~V., Zanis,~P., and Zerefos,~C.: Stratosphere-troposphere exchange – a~review, and what we have learned from STACCATO, STACCATO special section of J. Geophys. Res., 108, 8516, doi:10.1029/2002JD002490, 2003a. Stohl, A., Bonasoni, P., Cristofanelli, P., et al.: Stratosphere-troposphere exchange: a~review, and what we have learned from STACCATO, J. Geophys. Res., 108(D12), 8516, doi:10.1029/2002JD002490,~2003b. Stohl,~A., Wernli,~H., James,~P., Bourqui,~M., Forster,~C., Liniger~M A.,, Seibert~P., and Sprenger,~M.: A~new perspective of stratosphere-troposphere exchange, B. Am. Meteor. Soc., 84(11), 1563–1573, doi:10.1175/BAMS-84-11-1565, 2003c. Stohl, A., Forster, C., Frank, A., Seibert, P., and Wotawa, G.: Technical note: The Lagrangian particle dispersion model FLEXPART version 6.2, Atmos. Chem. Phys., 5, 2461–2474, doi:10.5194/acp-5-2461-2005, 2005. Tarasick,~D W. and Slater,~R.: Ozone in the troposphere: measurements, climatology, budget, and trends, Atmos. Ocean, 46, 93–115, doi:10.3137/ao.460105, 2008. Thompson,~A M., Stone,~J B., Witte,~J C., Miller,~S., Oltmans,~S J., Kucsera,~T L., Merrill,~J T., Forbes,~G., Tarasick,~D W., Joseph,~E., Schmidlin,~F J., MacMillan,~W W., Warner,~J., Hintsa,~E., and Johnson,~J.: Intercontinental chemical transport experiment ozonesonde network study (IONS) 2004: 2. Tropospheric ozone budgets and variability over Northeastern North America, J. Geophys. Res., 112, D12S13, doi:10.1029/2006JD007670, 2007. Tranchant, B. J. S. and Vincent, A. P.: Statistical interpolation of ozone measurements from satellite data (TOMS, SBUV and SAGE II) using the kriging method, Ann. Geophys., 18, 666–678, 2000. Vaughan,~G., Howells,~A., and Price,~J D.: Use of MST radars to probe the mesoscale structure of the tropopause, Tellus A, 47, 759–765, 1995. Wakamatsu,~S., Uno,~I., Ueda,~H., and Uehara,~K.: Observational study of stratospheric ozone intrusions into the lower troposphere, Atmos. Environ., 23(8), 1815–1826, 1989. Worden,~J., Sund-Kulawik,~S., Shephard,~M W., Clough,~S A., Worden,~H., Bowman,~K., and Goldman,~A.: Predicted errors of tropospheric emission spectrometer nadir retrievals from spectral window selection, J. Geophys. Res., 109(D9), D09308, doi:10.1029/2004JD004522, 2004. Zahn,~A. and Brenninkeijer,~C A M.: New directions: a~chemical tropopause defined, Atmos. Environ., 37, 439–440, 2003. Zanis,~P., Gerasopoulos,~E., Priller,~A., Schnabel,~C., Stohl,~A., Zerefos,~C., Gaggeler,~H W., Tobler,~L., Kubik,~P W., Kanter,~H J., Scheel,~H E., Luterbacher,~J., and Berger,~M.: An estimate of the impact of stratosphere-to-troposphere transport (STT) on the lower free tropospheric ozone over the Alps using $^10$Be and $^7$Be measurements, J. Geophys. Res., 108(D12), 8520, doi:10.1029/2002JD002604, 2003a. Zanis, P., Trickl, T., Stohl, A., Wernli, H., Cooper, O., Zerefos, C., Gaeggeler, H., Schnabel, C., Tobler, L., Kubik, P. W., Priller, A., Scheel, H. E., Kanter, H. J., Cristofanelli, P., Forster, C., James, P., Gerasopoulos, E., Delcloo, A., Papayannis, A., and Claude, H.: Forecast, observation and modelling of a deep stratospheric intrusion event over Europe, Atmos. Chem. Phys., 3, 763–777, doi:10.5194/acp-3-763-2003, 2003b.