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| Titel |
The Effect of the Interannual Variability of the OH Sink on the Interannual Variability of the Atmospheric Methane Mixing Ratio and Carbon Stable Isotope Composition |
| VerfasserIn |
Tonatiuh Guillermo Nuñez Ramirez, Sander Houweling, Julia Marshall, Jason Williams, Gordon Brailsford, Oliver Schneising, Martin Heimann |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250081843
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| Zusammenfassung |
| The atmospheric hydroxyl radical concentration (OH) varies due to changes in the incoming
UV radiation, in the abundance of atmospheric species involved in the production, recycling
and destruction of OH molecules and due to climate variability. Variability in carbon
monoxide emissions from biomass burning induced by El Niño Southern Oscillation are
particularly important. Although the OH sink accounts for the oxidation of approximately
90% of atmospheric CH4, the effect of the variability in the distribution and strength of the
OH sink on the interannual variability of atmospheric methane (CH4) mixing ratio and stable
carbon isotope composition (δ13C-CH4) has often been ignored. To show this effect we
simulated the atmospheric signals of CH4 in a three-dimensional atmospheric transport
model (TM3). ERA Interim reanalysis data provided the atmospheric transport and
temperature variability from 1990 to 2010. We performed simulations using time dependent
OH concentration estimations from an atmospheric chemistry transport model and an
atmospheric chemistry climate model. The models assumed a different set of reactions
and algorithms which caused a very different strength and distribution of the OH
concentration. Methane emissions were based on published bottom-up estimates
including inventories, upscaled estimations and modeled fluxes. The simulations also
included modeled concentrations of atomic chlorine (Cl) and excited oxygen atoms
(O(1D)). The isotopic signal of the sources and the fractionation factors of the sinks
were based on literature values, however the isotopic signal from wetlands and
enteric fermentation processes followed a linear relationship with a map of C4 plant
fraction. The same set of CH4emissions and stratospheric reactants was used in all
simulations. Two simulations were done per OH field: one in which the CH4 sources were
allowed to vary interannually, and a second where the sources were climatological.
The simulated mixing ratios and isotopic compositions at global reference stations
were used to construct more robust indicators such as global and zonal means and
interhemispheric differences. We also compared the model CH4 mixing ratio to satellite
observations, for the period 2003 to 2004 with SCIAMACHY and from 2009 to 2010
with GOSAT. The interannual variability of the different OH fields imprinted an
interannual variation of the atmospheric CH4 mixing ratio with a magnitude of ±10 ppb,
which is comparable to the effect of all sources combined. Meanwhile its effect
on the interannual variability of δ13C-CH4 was minor (< 10%). The interannual
variability of the mixing ratio interhemispheric difference is dominated by the sources
because the OH sink is concentrated in the tropics, thus its interannual variability
affects both hemispheres. Meanwhile, although the OH plays an important role in
the establishment of an interhemispheric gradient of δ13C-CH4, the interannual
variation of this gradient is negligibly affected by the choice of OH field. Overall
the study showed that the variability of the OH sink plays a significant role in the
interannual variability of the atmospheric methane mixing ratio, and must be considered
to improve our understanding of the recent trends in the global methane budget. |
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