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| Titel |
Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2) |
| VerfasserIn |
S. Tilmes, J.-F. Lamarque, L. K. Emmons, D. E. Kinnison, P.-L. Ma, X. Liu, S. Ghan, C. Bardeen, S. Arnold, M. Deeter, F. Vitt, T. Ryerson, J. W. Elkins, F. Moore, J. R. Spackman, M. Martin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 5 ; Nr. 8, no. 5 (2015-05-13), S.1395-1426 |
| Datensatznummer |
250116341
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| Publikation (Nr.) |
 copernicus.org/gmd-8-1395-2015.pdf |
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| Zusammenfassung |
| The Community Atmosphere Model (CAM), version 5, is now coupled to extensive
tropospheric and stratospheric chemistry, called CAM5-chem, and is available
in addition to CAM4-chem in the Community Earth System Model (CESM) version
1.2. The main focus of this paper is to compare the performance of
configurations with internally derived "free running" (FR) meteorology and
"specified dynamics" (SD) against observations from surface, aircraft, and
satellite, as well as understand the origin of the identified differences. We
focus on the representation of aerosols and chemistry. All model
configurations reproduce tropospheric ozone for most regions based on in situ
and satellite observations. However, shortcomings exist in the representation
of ozone precursors and aerosols. Tropospheric ozone in all model
configurations agrees for the most part with ozonesondes and satellite
observations in the tropics and the Northern Hemisphere within the
variability of the observations. Southern hemispheric tropospheric ozone is
consistently underestimated by up to 25%. Differences in convection and
stratosphere to troposphere exchange processes are mostly responsible for
differences in ozone in the different model configurations. Carbon monoxide
(CO) and other volatile organic compounds are largely underestimated in
Northern Hemisphere mid-latitudes based on satellite and aircraft
observations. Nitrogen oxides (NOx) are biased low in the free tropical
troposphere, whereas peroxyacetyl nitrate (PAN) is overestimated in
particular in high northern latitudes. The present-day methane lifetime
estimates are compared among the different model configurations. These range
between 7.8 years in the SD configuration of CAM5-chem and 8.8 years in the
FR configuration of CAM4-chem and are therefore underestimated compared to
observational estimations. We find that differences in tropospheric aerosol
surface area between CAM4 and CAM5 play an important role in controlling the
burden of the tropical tropospheric hydroxyl radical (OH), which causes
differences in tropical methane lifetime of about half a year between
CAM4-chem and CAM5-chem. In addition, different distributions of NOx from
lightning explain about half of the difference between SD and FR model
versions in both CAM4-chem and CAM5-chem. Remaining differences in the
tropical OH burden are due to enhanced tropical ozone burden in SD
configurations compared to the FR versions, which are not only caused by
differences in chemical production or loss but also by transport and mixing.
For future studies, we recommend the use of CAM5-chem configurations, due to
improved aerosol description and inclusion of aerosol–cloud interactions.
However, smaller tropospheric surface area density in the current version of
CAM5-chem compared to CAM4-chem results in larger oxidizing capacity in the
troposphere and therefore a shorter methane lifetime. |
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