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| Titel |
TransCom model simulations of CH4 and related species: linking transport, surface flux and chemical loss with CH4 variability in the troposphere and lower stratosphere |
| VerfasserIn |
P. K. Patra, S. Houweling, M. Krol, P. Bousquet, D. Belikov, D. Bergmann, H. Bian, P. Cameron-Smith, M. P. Chipperfield, K. Corbin, A. Fortems-Cheiney, A. Fraser, E. Gloor, P. Hess, A. Ito, S. R. Kawa, R. M. Law, Z. Loh, S. Maksyutov, L. Meng, P. I. Palmer, R. G. Prinn, M. Rigby, R. Saito, C. Wilson |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2011-12-19), S.12813-12837 |
| Datensatznummer |
250010280
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| Publikation (Nr.) |
 copernicus.org/acp-11-12813-2011.pdf |
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| Zusammenfassung |
| A chemistry-transport model (CTM) intercomparison experiment
(TransCom-CH4) has been designed to investigate the
roles of surface emissions, transport and chemical loss in
simulating the global methane distribution. Model simulations
were conducted using twelve models and four model variants and
results were archived for the period of 1990–2007. All but
one model transports were driven by reanalysis products from
3 different meteorological agencies. The transport and removal
of CH4 in six different emission scenarios were simulated,
with net global emissions of 513 ± 9 and
514 ± 14 Tg CH4 yr−1 for the 1990s and
2000s, respectively. Additionally, sulfur hexafluoride
(SF6) was simulated to check the interhemispheric
transport, radon (222Rn) to check the subgrid scale
transport, and methyl chloroform (CH3CCl3) to check
the chemical removal by the tropospheric hydroxyl radical
(OH). The results are compared to monthly or annual mean time
series of CH4, SF6 and CH3CCl3
measurements from 8 selected background sites, and to
satellite observations of CH4 in the upper troposphere
and stratosphere. Most models adequately capture the vertical
gradients in the stratosphere, the average long-term trends,
seasonal cycles, interannual variations (IAVs) and interhemispheric
(IH) gradients at the surface sites for SF6, CH3CCl3
and CH4. The vertical gradients of all tracers between
the surface and the upper troposphere are consistent within
the models, revealing vertical transport differences between
models. An average IH exchange time of 1.39 ± 0.18 yr
is derived from SF6 time series. Sensitivity simulations
suggest that the estimated trends in exchange time, over the
period of 1996–2007, are caused by a change of SF6
emissions towards the tropics.
Using six sets of emission scenarios, we show that the
decadal average CH4 growth rate likely reached
equilibrium in the early 2000s due to the flattening of
anthropogenic emission growth since the late 1990s. Up to
60% of the IAVs in the observed CH4
concentrations can be explained by accounting for the IAVs
in emissions, from biomass burning and wetlands, as
well as meteorology in the forward models. The
modeled CH4 budget is shown to depend strongly on the
troposphere-stratosphere exchange rate and thus on the model's
vertical grid structure and circulation in the lower
stratosphere. The 15-model median CH4 and
CH3CCl3 atmospheric lifetimes are estimated to be
9.99 ± 0.08 and 4.61 ± 0.13 yr, respectively,
with little IAV due to transport and temperature. |
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