Articles | Volume 16, issue 14
Atmos. Chem. Phys., 16, 8791–8815, 2016
Atmos. Chem. Phys., 16, 8791–8815, 2016

Research article 19 Jul 2016

Research article | 19 Jul 2016

How stratospheric are deep stratospheric intrusions? LUAMI 2008

Thomas Trickl1, Hannes Vogelmann1, Andreas Fix2, Andreas Schäfler2, Martin Wirth2, Bertrand Calpini3, Gilbert Levrat3, Gonzague Romanens3, Arnoud Apituley4,a, Keith M. Wilson4,b, Robert Begbie5, Jens Reichardt5, Holger Vömel5,c, and Michael Sprenger6 Thomas Trickl et al.
  • 1Karlsruher Institut für Technologie, Institut für Meteorologie und Klimaforschung, IMK-IFU, Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany
  • 2Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Münchner Str. 20, 82234 Weßling, Germany
  • 3Aerological Station, Federal Office of Meteorology and Climatology, MeteoSwiss, Chemin de l'Aérologie, P.O. Box 316, 1530 Payerne, Switzerland
  • 4RIVM, Antonie van Leeuwenhoeklaan 9, 3721 MA Bilthoven, the Netherlands
  • 5Richard-Aßmann-Observatorium, Deutscher Wetterdienst, Am Observatorium 12, 15848 Tauche, Ortsteil Lindenberg, Germany
  • 6Eidgenössische Technische Hochschule (ETH) Zürich, Institut für Atmosphäre und Klima, Universitätstraße 16, 8092 Zürich, Switzerland
  • anow at: KNMI, Utrechtseweg 297, 3731 GA De Bilt, the Netherlands
  • bnow at: Kipp en Zonen, Delftechpark 36, 2628 XH Delft, the Netherlands
  • cnow at: NCAR EOL FL-1, 3090 Center Green Drive, Boulder, Colorado 80301, USA

Abstract. A large-scale comparison of water-vapour vertical-sounding instruments took place over central Europe on 17 October 2008, during a rather homogeneous deep stratospheric intrusion event (LUAMI, Lindenberg Upper-Air Methods Intercomparison). The measurements were carried out at four observational sites: Payerne (Switzerland), Bilthoven (the Netherlands), Lindenberg (north-eastern Germany), and the Zugspitze mountain (Garmisch-Partenkichen, German Alps), and by an airborne water-vapour lidar system creating a transect of humidity profiles between all four stations. A high data quality was verified that strongly underlines the scientific findings. The intrusion layer was very dry with a minimum mixing ratios of 0 to 35 ppm on its lower west side, but did not drop below 120 ppm on the higher-lying east side (Lindenberg). The dryness hardens the findings of a preceding study (“Part 1”, Trickl et al., 2014) that, e.g., 73 % of deep intrusions reaching the German Alps and travelling 6 days or less exhibit minimum mixing ratios of 50 ppm and less. These low values reflect values found in the lowermost stratosphere and indicate very slow mixing with tropospheric air during the downward transport to the lower troposphere. The peak ozone values were around 70 ppb, confirming the idea that intrusion layers depart from the lowermost edge of the stratosphere. The data suggest an increase of ozone from the lower to the higher edge of the intrusion layer. This behaviour is also confirmed by stratospheric aerosol caught in the layer. Both observations are in agreement with the idea that sections of the vertical distributions of these constituents in the source region were transferred to central Europe without major change. LAGRANTO trajectory calculations demonstrated a rather shallow outflow from the stratosphere just above the dynamical tropopause, for the first time confirming the conclusions in “Part 1” from the Zugspitze CO observations. The trajectories qualitatively explain the temporal evolution of the intrusion layers above the four stations participating in the campaign.

Short summary
A rather homogeneous deep stratospheric intrusion event was mapped by vertical sounding over central Europe and by model calculations along the transport path. The very low minimum H2O mixing ratios demonstrate almost negligible mixing with tropospheric air during the downward transport. The vertical distributions of O3 and aerosol were transferred from the source region to Europe without major change. A rather shallow outflow from the stratosphere was found.
Final-revised paper