Articles | Volume 26, issue 5
Ann. Geophys., 26, 1207–1220, 2008

Special issue: The fourth IAGA-ICMA-CAWSES Workshop "Long-Term Changes and...

Ann. Geophys., 26, 1207–1220, 2008

  28 May 2008

28 May 2008

Ozone trends at northern mid- and high latitudes – a European perspective

N. R. P. Harris1,12, E. Kyrö2, J. Staehelin3, D. Brunner4, S.-B. Andersen5,*, S. Godin-Beekmann6, S. Dhomse7, P. Hadjinicolaou8,9, G. Hansen10, I. Isaksen11, A. Jrrar12,**, A. Karpetchko2, R. Kivi2, B. Knudsen5, P. Krizan13, J. Lastovicka13, J. Maeder3, Y. Orsolini10, J. A. Pyle12, M. Rex14, K. Vanicek15, M. Weber7, I. Wohltmann14, P. Zanis16, and C. Zerefos8 N. R. P. Harris et al.
  • 1European Ozone Research Coordinating Unit, University of Cambridge, UK
  • 2Arctic Research Centre of Finnish Meteorological Institute, Sodankylä, Finland
  • 3Swiss Federal Institute of Technology, Zurich, Switzerland
  • 4Empa, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf, Switzerland
  • 5Danish Meteorological Institute, Copenhagen, Denmark
  • 6CNRS-Service d'Aéronomie, Université Pierre et Marie Curie, Paris, France
  • 7University of Bremen, Bremen, Germany
  • 8National and Kapodistrian University of Athens, Greece
  • 9Frederick Institute of Technology, Nicosia, Cyprus
  • 10Norwegian Institute for Air Research, Norway
  • 11University of Oslo, Oslo, Norway
  • 12Centre for Atmospheric Science, University of Cambridge, UK
  • 13Institute of Atmospheric Physics, Academy of the Sciences of the Czech Republic
  • 14Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany
  • 15Czech Hydrometeorological Institute, Czech Republic
  • 16Department of Meteorology – Climatology, Aristotle University of Thessaloniki, Thessaloniki, Greece
  • *now at: the Danish and Greenlandic Survey, Copenhagen, Denmark
  • **now at: British Antarctic Survey, Cambridge, UK

Abstract. The EU CANDIDOZ project investigated the chemical and dynamical influences on decadal ozone trends focusing on the Northern Hemisphere. High quality long-term ozone data sets, satellite-based as well as ground-based, and the long-term meteorological reanalyses from ECMWF and NCEP are used together with advanced multiple regression models and atmospheric models to assess the relative roles of chemistry and transport in stratospheric ozone changes. This overall synthesis of the individual analyses in CANDIDOZ shows clearly one common feature in the NH mid latitudes and in the Arctic: an almost monotonic negative trend from the late 1970s to the mid 1990s followed by an increase. In most trend studies, the Equivalent Effective Stratospheric Chlorine (EESC) which peaked in 1997 as a consequence of the Montreal Protocol was observed to describe ozone loss better than a simple linear trend. Furthermore, all individual analyses point to changes in dynamical drivers, such as the residual circulation (responsible for the meridional transport of ozone into middle and high latitudes) playing a key role in the observed turnaround. The changes in ozone transport are associated with variations in polar chemical ozone loss via heterogeneous ozone chemistry on PSCs (polar stratospheric clouds). Synoptic scale processes as represented by the new equivalent latitude proxy, by conventional tropopause altitude or by 250 hPa geopotential height have also been successfully linked to the recent ozone increases in the lowermost stratosphere. These show significant regional variation with a large impact over Europe and seem to be linked to changes in tropospheric climate patterns such as the North Atlantic Oscillation. Some influence in recent ozone increases was also attributed to the rise in solar cycle number 23. Changes from the late 1970s to the mid 1990s were found in a number of characteristics of the Arctic vortex. However, only one trend was found when more recent years are also considered, namely the tendency for cold winters to become colder.