Atmospheric Chemistry and Physics Discussions
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10.5194/acpd-7-3451-2007
http://www.atmos-chem-phys-discuss.net/7/3451/2007/
http://www.atmos-chem-phys-discuss.net/7/3451/2007/acpd-7-3451-2007.html
http://www.atmos-chem-phys-discuss.net/7/3451/2007/acpd-7-3451-2007.pdf
3451
3517
2007-03-06
A UT/LS ozone climatology of the nineteen seventies deduced from the GASP aircraft measurement program
C. Schnadt Poberaj
christina.schnadt@env.ethz.ch
J. Staehelin
D. Brunner
V. Thouret
V. Mohnen
Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
Laboratory for Air Pollution/Environmental Technology, Empa, Dübendorf, Switzerland
Laboratoire d'Aérologie, UMR 5560, Université Paul Sabatier, Toulouse, France
Atmospheric Sciences Research Center, State University of New York at Albany, Albany, New York, USA
The knowledge of historical ozone in the upper troposphere/lower
stratosphere (UT/LS) region is mostly confined to regular measurements from
a number of ozonesonde stations. We present ozone measurements of the Global
Atmospheric Sampling Program (GASP) performed from four commercial and one
research aircraft during 1975 to 1979. Using GASP data, a UT/LS ozone
climatology of 1975–1979 was built. Seasonality and concentrations of GASP
UT ozone in the middle, subtropical and tropical regions of the northern
hemisphere (NH) are generally in agreement with other published
observations, derived from ozonesondes or aircraft campaigns. In regions
where both GASP (1970s) and MOZAIC (1990s) data are available, similar ozone
concentrations are found and seasonal cycles agree well confirming the
reliability of GASP ozone. GASP provides unique large-scale climatological
information on UT/LS ozone above the NH Pacific region. Agreement is found
with observations from individual ozonesonde sites and aircraft campaigns
carried out over this region. Tropical UT ozone is seen to be lower near the
dateline than further east, presumably related to uplift of ozone poor air
within convection. Over the west coast of the United States, summer UT ozone
is higher than over the adjacent Pacific, probably caused by air pollution
over southern California in the 1970s. GASP offers an unprecedented
opportunity to link to European, Canadian and U.S. American ozonesonde
observations of the 1970s. For the quantitative comparison, an altitude
offset was applied to the sonde data to account for the slow response time
of the sensors. In the LS, the European and Canadian Brewer-Mast (BM)
sensors then agree to ±10% with the GASP instruments in all
seasons. In the UT, the European BM sondes record similar to slightly less
average ozone than GASP, however, with large variability overlaid. Over the
eastern United States, systematic positive deviations of the Wallops Island
ECC sondes from GASP of +20% are found. The comparisons over Europe and
the eastern United States corroborate earlier findings that the early ECC
sensors may have measured 10 to 25% more ozone than the BM sensors. Our
results further indicate that applying the correction factor to the 1970s BM
ozonesondes is necessary to yield reliable ozone mixing ratios in the UT/LS.
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