Atmospheric Chemistry and Physics Discussions
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2007
10.5194/acpd-7-17179-2007
http://www.atmos-chem-phys-discuss.net/7/17179/2007/
http://www.atmos-chem-phys-discuss.net/7/17179/2007/acpd-7-17179-2007.html
http://www.atmos-chem-phys-discuss.net/7/17179/2007/acpd-7-17179-2007.pdf
17179
17211
2007-11-26
Ozone-enhanced layers in the troposphere over the equatorial Pacific Ocean and the influence of transport of midlatitude UT/LS air
H. Hayashi
K. Kita
kita@mx.ibaraki.ac.jp
S. Taguchi
Department of Environmental Sciences, College of Science, Ibaraki University, Mito, Japan
Research Institute for Environmental Management Technology, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
Occurrence of ozone (O<sub>3</sub>)-enhanced layers in the troposphere over the
equatorial Pacific Ocean and their seasonal variation were investigated
based on ozonesonde data obtained at three Southern Hemisphere ADditional
OZonesondes (SHADOZ) sites, Watukosek, American Samoa and San Cristobal, for
6 years between 1998 and 2003. O<sub>3</sub>-enhanced layers were found in about
50% of observed O<sub>3</sub> profiles at the three sites on yearly average.
The formation processes of O<sub>3</sub>-enhanced layers were investigated by
meteorological analyses including backward trajectories. On numerous
occasions, O<sub>3</sub>-enhanced layers resulted from the transport of air masses
affected by biomass burning. The contribution of this process was about
30% at San Cristobal during the periods from February to March and from
August to September, while it was relatively low, about 10%, at Watukosek
and Samoa. A significant number of the O<sub>3</sub>-enhanced layers were
attributed to the transport of midlatitude upper-troposphere and
lower-stratosphere (UT/LS) air. Meteorological analyses indicated that these
layers originated from equatorward and downward transport of the midlatitude
UT/LS air masses through a narrow region between high- and low-pressure
systems around the subtropical jet stream. This process accounted for more
than 40% at Watukosek between May and December, about 60% or more at
Samoa all year around, and about 40% at San Cristobal between November
and March, indicating that it was important for O<sub>3</sub> budget over the
equatorial Pacific Ocean.
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