Methane chemistry in a nutshell – the new submodels CH4 (v1.0) and TRSYNC (v1.0) in MESSy (v2.54.0)
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Published:2021-02-02
Issue:2
Volume:14
Page:661-674
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ISSN:1991-9603
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Container-title:Geoscientific Model Development
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language:en
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Short-container-title:Geosci. Model Dev.
Author:
Winterstein FranziskaORCID, Jöckel PatrickORCID
Abstract
Abstract. Climate projections including chemical feedbacks rely on state-of-the-art
chemistry–climate models (CCMs). Of particular importance is the role of
methane (CH4) for the budget of stratospheric water vapour (SWV),
which has an important climate impact. However, simulations with CCMs are, due
to the large number of involved chemical species, computationally demanding,
which limits the simulation of sensitivity studies. To allow for sensitivity studies and ensemble simulations with a reduced
demand for computational resources, we introduce a simplified approach to
simulate the core of methane chemistry in form of the new Modular Earth
Submodel System (MESSy) submodel CH4. It involves an atmospheric
chemistry mechanism reduced to the sink reactions of CH4 with predefined
fields of the hydroxyl radical (OH), excited oxygen (O(1D)), and
chlorine (Cl), as well as photolysis and the reaction products limited
to water vapour (H2O). This chemical production of H2O is
optionally fed back onto the specific humidity (q) of the connected
general circulation model (GCM), to account for the impact onto
SWV and its effect on radiation and stratospheric dynamics. The submodel CH4 is further capable of simulating the four most prevalent
CH4 isotopologues for carbon and hydrogen (CH4 and CH3D, as
well as 12CH4 and 13CH4). Furthermore, the
production of deuterated water vapour (HDO) is, similar to the
production of H2O in the CH4 oxidation, optionally passed back to
the isotopological hydrological cycle simulated by the submodel H2OISO,
using the newly developed auxiliary submodel TRSYNC. Moreover, the
simulation of a user-defined number of diagnostic CH4 age and emission
classes is possible, the output of which can be used for offline inverse optimization
techniques. The presented approach combines the most important chemical hydrological
feedback including the isotopic signatures with the advantages concerning the
computational simplicity of a GCM, in comparison to a full-featured
CCM.
Publisher
Copernicus GmbH
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