Long-term changes in UT/LS ozone between the late 1970s and the 1990s deduced from the GASP and MOZAIC aircraft programs and from ozonesondes 1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
2Laboratory for Air Pollution/Environmental Technology, Empa, Dübendorf, Switzerland
3Laboratoire d'Aérologie, Université de Toulouse, CNRS, Toulouse, France
4Royal Meteorological Institute of Belgium (KMI-IRM), Brussels, Belgium
5Federal Office of Meteorology and Climatology MeteoSwiss, Aerological Station, Payerne, Switzerland
Received: 04 Nov 2008 – Published in Atmos. Chem. Phys. Discuss.: 27 Jan 2009 – Published: 29 Jul 2009Abstract. We present ozone measurements of the Global Atmospheric Sampling Program
(GASP) performed from four commercial and one research aircraft in the late
1970s to compare them with respective measurements of the ongoing MOZAIC
project. Multi-annual averages of UT/LS ozone were built using the aircraft data
sets (1975–1979 and 1994–2001), and long-term changes between the 1970s and
1990s were derived by comparison. The data were binned relative to the
dynamical tropopause to separate between UT and LS air masses. LS data were
analysed using equivalent latitudes. In the UT, pronounced increases of 20–40%
are found over the Middle East and South Asia in the spring and summer seasons.
Increases are also found over Japan, Europe, and the eastern parts of the
United States depending on season. LS ozone over northern mid- and high
latitudes was found to be lower in the 1990s compared to the 1970s in all
seasons of the year. In addition, a comparison with long-term changes
deduced from ozonesondes is presented. The early 1970s European Brewer-Mast (BM)
sonde data agree with GASP within the range of uncertainty (UT) or measured
slightly less ozone (LS). In contrast, the 1990s BM sensors show consistently
and significantly higher UT/LS ozone values than MOZAIC. This unequal behaviour
of aircraft/sonde comparisons in the 1970s and 1990s leads to differences in
the estimated long-term changes
over Europe: while the comparison between GASP and MOZAIC indicates ozone
changes of −5% to 10% over Europe, the sondes suggest a much larger
increase of 10%–35% depending on station and season, although
statistical significance is not conclusive due to data sample limitations.
In contrast to the BM sondes, the Electrochemical Cell (ECC) sonde at
Wallops Island, USA, measured higher UT ozone than both GASP and MOZAIC.
Hence, long-term changes from GASP/MOZAIC agree within the range of
uncertainty with the changes deduced from Wallops Island.
Citation: Schnadt Poberaj, C., Staehelin, J., Brunner, D., Thouret, V., De Backer, H., and Stübi, R.: Long-term changes in UT/LS ozone between the late 1970s and the 1990s deduced from the GASP and MOZAIC aircraft programs and from ozonesondes, Atmos. Chem. Phys., 9, 5343-5369, doi:10.5194/acp-9-5343-2009, 2009.