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| Titel |
Comparison of the HadGEM2 climate-chemistry model against in situ and SCIAMACHY atmospheric methane data |
| VerfasserIn |
G. D. Hayman, F. M. O'Connor, M. Dalvi, D. B. Clark, N. Gedney, C. Huntingford, C. Prigent, M. Buchwitz, O. Schneising, J. P. Burrows, C. Wilson, N. Richards, M. Chipperfield |
| 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 ; 14, no. 23 ; Nr. 14, no. 23 (2014-12-12), S.13257-13280 |
| Datensatznummer |
250119236
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| Publikation (Nr.) |
 copernicus.org/acp-14-13257-2014.pdf |
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| Zusammenfassung |
Wetlands are a major emission source of methane (CH4)
globally. In this study, we evaluate wetland emission
estimates derived using the UK community land surface model (JULES,
the Joint UK Land Earth Simulator) against atmospheric observations
of methane, including, for the first time, total methane columns
derived from the SCIAMACHY instrument on board the ENVISAT
satellite.
Two JULES wetland emission estimates are investigated: (a) from an
offline run driven with Climatic Research Unit–National Centers for Environmental Prediction
(CRU-NCEP) meteorological data and (b) from
the same offline run in which the modelled wetland fractions are
replaced with those derived from the Global Inundation Extent from
Multi-Satellites (GIEMS) remote sensing product. The mean annual
emission assumed for each inventory (181 Tg CH4 per annum
over the period 1999–2007) is in line with other recently published
estimates. There are regional differences as the unconstrained
JULES inventory gives significantly higher emissions in the Amazon
(by ~36 Tg CH4 yr−1)
and lower emissions in other regions
(by up to 10 Tg CH4 yr−1)
compared to the JULES estimates
constrained with the GIEMS product.
Using the UK Hadley Centre's Earth System model with atmospheric
chemistry (HadGEM2), we evaluate these JULES wetland emissions
against atmospheric observations of methane. We obtain improved
agreement with the surface concentration measurements, especially at
high northern latitudes, compared to previous HadGEM2 runs using the
wetland emission data set of Fung et al. (1991). Although the modelled
monthly atmospheric methane columns reproduce the large-scale
patterns in the SCIAMACHY observations, they are biased low by 50
part per billion by volume (ppb). Replacing the HadGEM2 modelled
concentrations above 300 hPa with HALOE–ACE assimilated
TOMCAT output results in a significantly better agreement with the
SCIAMACHY observations. The use of the GIEMS product to constrain
the JULES-derived wetland fraction improves the representation of the
wetland emissions in JULES and gives a good description of the
seasonality observed at surface sites influenced by wetlands,
especially at high latitudes. We find that the annual cycles
observed in the SCIAMACHY measurements and at many of the surface
sites influenced by non-wetland sources cannot be reproduced in
these HadGEM2 runs. This suggests that the emissions over certain
regions (e.g. India and China) are possibly too high and/or the
monthly emission patterns for specific sectors are incorrect.
The comparisons presented in this paper show that the
performance of the JULES wetland scheme is comparable to that of
other process-based land surface models. We identify areas
for improvement in this and the atmospheric chemistry components of
the HadGEM Earth System model. The Earth Observation data sets used
here will be of continued value in future evaluations of JULES and
the HadGEM family of models. |
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