Climatology and long-term evolution of ozone and carbon monoxide in the upper troposphere–lower stratosphere (UTLS) at northern midlatitudes, as seen by IAGOS from 1995 to 2013
In situ measurements in the upper troposphere–lower stratosphere (UTLS) have been performed in the framework of the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System) for ozone since 1994 and for carbon monoxide (CO) since 2002. The flight tracks cover a wi...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/5415/2018/acp-18-5415-2018.pdf |
| Summary: | In situ measurements in the upper troposphere–lower stratosphere (UTLS) have
been performed in the framework of the European research infrastructure IAGOS
(In-service Aircraft for a Global Observing System) for ozone since 1994 and
for carbon monoxide (CO) since 2002. The flight tracks cover a wide range of
longitudes in the northern extratropics, extending from the North American
western coast (125° W) to the eastern Asian coast (135° E)
and more recently over the northern Pacific Ocean. Several tropical regions
are also sampled frequently, such as the Brazilian coast, central and
southern Africa, southeastern Asia, and the western half of the Maritime
Continent. As a result, a new set of climatologies for O<sub>3</sub>
(August 1994–December 2013) and CO (December 2001–December 2013) in the
upper troposphere (UT), tropopause layer, and lower stratosphere (LS) are made
available, including gridded horizontal distributions on a semi-global scale
and seasonal cycles over eight well-sampled regions of interest in the
northern extratropics. The seasonal cycles generally show a summertime
maximum in O<sub>3</sub> and a springtime maximum in CO in the UT, in contrast to
the systematic springtime maximum in O<sub>3</sub> and the quasi-absence of a seasonal cycle of CO in the LS. This study highlights some regional
variabilities in the UT, notably (i) a west–east difference of O<sub>3</sub> in
boreal summer with up to 15 ppb more O<sub>3</sub> over central Russia compared
with northeast America, (ii) a systematic west–east gradient of CO from 60
to 140° E, especially noticeable in spring and summer with about
5 ppb by 10 degrees longitude, (iii) a broad spring/summer maximum of CO
over northeast Asia, and (iv) a spring maximum of O<sub>3</sub> over western North
America. Thanks to almost 20 years of O<sub>3</sub> and 12 years of CO
measurements, the IAGOS database is a unique data set to derive trends in the
UTLS at northern midlatitudes. Trends in O<sub>3</sub> in the UT are positive and
statistically significant in most regions, ranging from +0.25 to
+0.45 ppb yr<sup>−1</sup>, characterized by the significant increase in the
lowest values of the distribution. No significant trends of O<sub>3</sub> are
detected in the LS. Trends of CO in the UT, tropopause, and LS are almost all
negative and statistically significant. The estimated slopes range from
−1.37 to −0.59 ppb yr<sup>−1</sup>, with a nearly homogeneous decrease in the
lowest values of the monthly distribution (5th percentile) contrasting with
the high interregional variability in the decrease in the highest values
(95th percentile). |
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| ISSN: | 1680-7316 1680-7324 |