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| Titel |
Seasonal changes in the tropospheric carbon monoxide profile over the remote Southern Hemisphere evaluated using multi-model simulations and aircraft observations |
| VerfasserIn |
J. A. Fisher, S. R. Wilson, G. Zeng, J. E. Williams, L. K. Emmons, R. L. Langenfelds, P. B. Krummel, L. P. Steele |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 6 ; Nr. 15, no. 6 (2015-03-23), S.3217-3239 |
| Datensatznummer |
250119569
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| Publikation (Nr.) |
 copernicus.org/acp-15-3217-2015.pdf |
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| Zusammenfassung |
| The combination of low anthropogenic emissions and large biogenic
sources that characterizes the Southern Hemisphere (SH) leads to significant
differences in atmospheric composition relative to the better studied Northern
Hemisphere. This unique balance of sources poses significant challenges
for global models. Carbon monoxide (CO) in particular is difficult to simulate
in the SH due to the increased importance of secondary chemical production
associated with the much more limited primary emissions.
Here, we use aircraft observations from the 1991–2000 Cape Grim
Overflight Program (CGOP) and the 2009–2011 HIAPER (High-performance
Instrumented Airborne Platform for Environmental Research)
Pole-to-Pole Observations (HIPPO), together with model output from the SH
Model Intercomparison Project, to elucidate the drivers of
CO vertical structure in the remote SH. Observed CO vertical profiles from Cape Grim are
remarkably consistent with those observed over
the southern mid-latitudes Pacific 10–20 years later, despite major
differences in time periods, flight locations, and sampling
strategies between the two data sets. These similarities suggest
the processes driving observed vertical gradients are
coherent across much of the remote SH and have not changed
significantly over the past 2 decades. Model ability to simulate CO profiles
reflects the interplay between biogenic emission sources, the chemical
mechanisms that drive CO production from these sources,
and the transport that redistributes this CO throughout the SH. The four chemistry-climate
and chemical transport models included in the intercomparison show large variability in their abilities
to reproduce the observed CO profiles. In particular, two of the four models significantly
underestimate vertical gradients in austral summer and autumn, which we find
are driven by long-range transport of CO produced from oxidation of biogenic compounds.
Comparisons between the models show that more complex chemical mechanisms
do not necessarily provide more accurate simulation of CO vertical gradients
due to the convolved impacts of emissions, chemistry, and transport.
Our results imply a large sensitivity of the
remote SH troposphere to biogenic emissions and
chemistry, both of which remain key uncertainties in global modeling.
We suggest that the CO vertical gradient
can be used as a metric for future model evaluation as it provides
a sensitive test of the processes that define
the chemical state of the background atmosphere. |
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